Research, Development, and Technology

Turner-Fairbank Highway Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

Availability, Feasibility, and Reliability 

of Available Nondestructive Evaluation 

(NDE) Technologies for Detecting and 

Locating Buried Utilities: Final Report

PUBLICATION NO. FHWA-HRT-23-037 JULY 2023 
FOREWORD

This final report presents the use of promising nondestructive evaluation (NDE) and geophysical 

techniques for the detection of buried underground utilities. The project was conducted in stages, 

including a literature review, controlled laboratory testing, and field experiments to assess

performance under real-world conditions. As a result of this research, a new module will be 

added to Federal Highway Administration (FHWA) InfoTechnology web portal.

Bridge and pavement owners, consultants, contractors, and technical experts interested in

underground utilities are expected to benefit from the information contained herein. 

Jean A. Nehme, Ph.D., P.E.

Director, Office of Infrastructure 

Research and Development 

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation 

(USDOT) in the interest of information exchange. The U.S. Government assumes no liability for

the use of the information contained in this document. 

The U.S. Government does not endorse products or manufacturers. Trademarks or 

manufacturers’ names appear in this report only because they are considered essential to the 

objective of the document. 

Quality Assurance Statement

FHWA provides high-quality information to serve Government, industry, and the public in a 

manner that promotes public understanding. Standards and policies are used to ensure and

maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically

reviews quality issues and adjusts its programs and processes to ensure continuous quality

improvement. 
TECHNICAL REPORT DOCUMENTATION PAGE

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized. 

1. Report No.

FHWA-HRT-23-037

2. Government Accession No. 3. Recipient’s Catalog No.

4. Title and Subtitle

Availability, Feasibility, and Reliability of Available

Nondestructive Evaluation (NDE) Technologies for

Detecting and Locating Buried Utilities: Final Report

5. Report Date

July 2023

6. Performing Organization Code:

7. Author(s)

Delaine Reiter, Vanessa Napoli, Jeff Cohen, Shane Boone,

Patrick Moseley, Ahmad Alhasan, Jeremy Salerno

8. Performing Organization Report No.

9. Performing Organization Name and Address

Applied Research Associates

4300 San Mateo Blvd, NE, Ste. 200

Albuquerque, NM 87110

10. Work Unit No.

11. Contract or Grant No.

693JJ320C000005

12. Sponsoring Agency Name and Address

Office of Infrastructure Research and Development

Federal Highway Administration

6300 Georgetown Pike

McLean, VA 22101-2296

13. Type of Report and Period Covered

Final Report: April 2020–August 2022

14. Sponsoring Agency Code

HRDI-30 

15. Supplementary Notes

The Contracting Officer’s Representative was Frank Jalinoos (HRDI-30), ORCID: 0000-0001-8330-7603

16. Abstract

Modern nondestructive evaluation (NDE) technologies offer an expanding suite of geophysical techniques to

detect and locate buried utilities. This project focused on identifying promising technologies that merit expanded

application and mainstream deployment by State transportation departments. The project team applied a staged

approach to the effort, which included a thorough review of the open scientific literature, controlled testing of

candidate NDE technologies, and field experiments to assess performance under real-world conditions.

17. Key Words

Nondestructive evaluation, buried utility detection

and location

18. Distribution Statement

No restrictions. This document is available to the public

through the National Technical Information Service,

Springfield, VA 22161.

http://www.ntis.gov

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

70 

22. Price

N/A
ii

 

 

 

 

 

 
iii

TABLE OF CONTENTS

EXECUTIVE SUMMARY .......................................................................................................... 1

CHAPTER 1. INTRODUCTION ................................................................................................ 3

CHAPTER 2. CANDIDATE NDE TECHNOLOGIES TO DETECT AND LOCATE 

BURIED UTILITIES........................................................................................................ 5

EM Methods ............................................................................................................................ 5

GPR ..................................................................................................................................... 5

Low-Frequency EM Instruments: Pipe and Cable Locators ............................................... 8

FDEM Method: Terrain Conductivity Method ................................................................... 9

Magnetic Methods ................................................................................................................. 10

Magnetic Locators ............................................................................................................ 10

Magnetometers .................................................................................................................. 11

Seismic and Acoustic Methods ............................................................................................. 11

Traditional Acoustic Methods........................................................................................... 12

Seismic Methods ............................................................................................................... 12

Summary ................................................................................................................................ 14

CHAPTER 3. STATE DOT IMPLEMENTATION ................................................................ 17

CHAPTER 4. CONTROLLED LAB AND FIELD EXPERIMENTS ................................... 21

Test Methods and Instrumentation ..................................................................................... 24

Stepped-Frequency GPR Field Plan and Results .............................................................. 24

Pipe and Cable Locators Field Plan and Results .............................................................. 27

APL Field Plan and Results .............................................................................................. 28

FDEM Instrument Field Plan and Results ........................................................................ 29

HVSR Field Plan and Results ........................................................................................... 30

Controlled Laboratory Conclusions .................................................................................... 33

CHAPTER 5. FIELD EXPERIMENTS—VIRGINIA DOT SITES ...................................... 35

Data Acquisition Methods and Results ............................................................................... 38

GPR Field Plan and Results .............................................................................................. 38

MASW Field Plan and Results ......................................................................................... 44

APL Field Plan and Results .............................................................................................. 49

FDEM Instrument Field Plan and Results ........................................................................ 50

Field Test Conclusions .......................................................................................................... 52

CHAPTER 6. NDE TECHNOLOGY RECOMMENDATIONS ........................................... 53

ACKNOWLEDGMENTS .......................................................................................................... 57

REFERENCES ............................................................................................................................ 59
iv

LIST OF FIGURES

Figure 1. Image. Single GPR scan compiled by a survey vehicle identifying buried 

objects, which are indicated by the arrows pointed at the hyperbola. ...........................6

Figure 2. Illustration. Plan view synthetic data presentation of GPR antenna traveling 

over concrete with steel reinforcement with B-scan GPR data presented in 

reference to the scan location. ........................................................................................7

Figure 3. Photo. Air-coupled, step-frequency GPR mounted on a vehicle for underground 

utility location under roadway. ......................................................................................8

Figure 4. Image. Pseudo 3D HVSR section generated from multiple geophones (Khalil, 

Anukwu, and Nordin 2020). ........................................................................................14

Figure 5. Chart. Survey response from DOTs regarding internal and external use of NDE 

technologies. ................................................................................................................17

Figure 6. Graph. Survey response regarding types of NDE technologies used. ......................18

Figure 7. Graph. Survey response on which types of NDE technologies are reliable to 

inform engineering and construction judgments..........................................................18

Figure 8. Graph. Survey response on influence factors on adopting new NDE 

technologies for utility location. ..................................................................................19

Figure 9. Graph. Survey response regarding the ranking of improvements needed for the 

implementation and/or application of NDE technologies for utility location 

services. ........................................................................................................................20

Figure 10. Illustration. Soil box specimen with six total beds of cohesive soil stacked 

together. .......................................................................................................................22

Figure 11. Illustration. Soil box specimen with six total beds of cohesionless soil stacked 

together. .......................................................................................................................22

Figure 12. Illustration. Soil box specimen with six total beds of cohesive and 

cohesionless soil stacked together. ..............................................................................23

Figure 13. Illustration. Soil box specimen with six total beds of cohesionless and 

cohesive soil stacked together. .....................................................................................23

Figure 14. Photo. First level of soil box specimens with buried utilities in parallel. ..............24

Figure 15. Photo. GPR system with integrated cart scanning soil box. ...................................24

Figure 16. Image. GPR scans collected on cohesive soil test specimen, where each of the 

hyperbolic peaks represents a buried utility observed in the data. ..............................25

Figure 17. Image. GPR scans collected on cohesionless soil test specimen, where each of 

the hyperbolic peaks represents a buried utility observed in the data..........................25

Figure 18. Image. GPR scans collected on cohesive-cohesionless soil test specimen, 

where each of the hyperbolic peaks represents a buried utility observed in the 

data. ..............................................................................................................................26

Figure 19. Image. GPR scans collected on cohesionless-cohesive soil test specimen, 

where each of the hyperbolic peaks represents a buried utility observed in the 

data. ..............................................................................................................................26

Figure 20. Photo. Underground utilities locator scanning over steel pipe. ..............................28

Figure 21. Photo. APL in operation. ........................................................................................29

Figure 22. Photo. Ground conductivity meter in operation. ....................................................29
v 

Figure 23. Graph. Example of FDEM scan with two steel pipes indicated by local 

minimums. ...................................................................................................................30

Figure 24. Photo. HVSR four-sensor test setup for soil box 1, lift 4. ......................................31

Figure 25. Graphs. HVSR plots to confirm the presence of any pipes. ...................................32

Figure 26. Photo. Aerial view of the Spring Hill field site with utility locations, 

elevations, and type indicated with solid (sewer) or dashed (water) lines. ..................36

Figure 27. Photo. Aerial view of the Settlers Ridge field test site with utility locations, 

elevations, and types indicated with solid (sewer) or dashed (water) lines. ................37

Figure 28. Photo. Aerial view of the Windsong Way field test site with utility locations, 

elevations, and types indicated with solid (sewer) or dashed (water) lines. ................38

Figure 29. Photo. GPR system with DF antenna. ....................................................................39

Figure 30. Photos. Photo on left shows a stepped-frequency GPR system mounted on a 

travel vehicle, and photo on right shows a total station surveying system used to 

track the GPR antenna positions. .................................................................................40

Figure 31. Image. Example of the DF antenna GPR scan collected during field testing at 

Spring Hill (scan line identification 2 in table 4). ........................................................41

Figure 32. Image. Images show an example of a stepped-frequency GPR scan collected 

during field testing at Windsong Way. ........................................................................43

Figure 33. Photo. MASW data collection using a streamer geophone array at Settlers 

Ridge setup 9, deployed on asphalt..............................................................................44

Figure 34. Graph. MASW data-acquisition strategy used during field testing denotes a 

“shoot-through” approach where the geophone array remained in place and the 

source positions varied. ................................................................................................45

Figure 35. Image. SR11 2D shear-velocity profile versus depth. Two anomalous low‐

velocity zones appear near the expected locations of buried utility lines (Jalinoos 

2022). ...........................................................................................................................48

Figure 36. Image. SR7 2D shear wave velocity profile showing an anomalous lowvelocity zone near the depth of the target pipe (4-inch PVC water line). ....................49

Figure 37. Photo. APL system in use during field testing. ......................................................50

Figure 38. Image. Example of an APL scan collected during field testing. ............................50

Figure 39. Photo. FDEM system in use during field testing. ...................................................51

Figure 40. Image. Typical example of an FDEM scan collected during field testing 

(Settlers Ridge, scan line 6). ........................................................................................52
vi 

LIST OF TABLES

Table 1. Summary of researched NDE technologies. ..............................................................15

Table 2. Summary of maximum observable lift allowing visualization of subsurface 

target with GPR............................................................................................................27

Table 3. Summary of maximum observable lift allowing visualization of subsurface 

target with FDEM. .......................................................................................................30

Table 4. Scan line metadata and respective utility targets for the DF antenna GPR tests, 

including the system’s success or failure to detect targets. .........................................42

Table 5. MASW experimental setups and utility detection results. .........................................47

Table 6. Recommendations of NDE technologies. ..................................................................54
vii 

LIST OF ABBREVIATIONS

1D one-dimensional 

2D two-dimensional 

3D three-dimensional 

AC alternating current

APL acoustic pipe locator

DF dual frequency

DOT department of transportation 

EM electromagnetic

FDEM frequency-domain electromagnetic

FHWA Federal Highway Administration

GPR ground-penetrating radar

GPS Global Positioning System

HVSR horizontal-to-vertical spectral ratio

MASW multichannel analysis of surface waves

NDE nondestructive evaluation

PVC polyvinyl chloride 

SASW spectral analysis of surface waves

SHRP 2 Second Strategic Highway Research Program

TDEM time-domain electromagnetic

VDOT Virginia Department of Transportation 

Vs shear velocity

1 

EXECUTIVE SUMMARY

Modern nondestructive evaluation (NDE) technologies offer an expanding suite of geophysical 

techniques to detect and locate buried utilities. This project focused on identifying promising 

technologies that merit expanded application and mainstream deployment by State transportation 

departments. The project team applied a staged approach to the effort, which included a thorough review

of the open scientific literature, controlled testing of candidate NDE technologies, and field experiments 

to assess performance under real-world conditions. 

The literature review identified several current and emerging NDE technologies that could improve the 

detection and location of underground utilities across four geophysical domains: magnetic technologies, 

electromagnetic (EM) technologies, acoustic technologies, and seismic technologies. The project team

gathered capability information for NDE mapping techniques across a diverse array of conditions and 

applications. Some of the identified NDE technologies, such as traditional ground-penetrating radar

(GPR) methods and pile-and-cable locators, have already been broadly deployed in subsurface utilities

location projects. Other technologies, such as stepped-frequency GPR and multichannel analysis of 

surface waves (MASW), show increasing promise in field tests and continue to undergo improvements 

in data acquisition and high-resolution mapping. 

In the second phase of the project, the team assessed the capabilities of NDE technologies under 

controlled laboratory conditions to establish performance baselines and compare the strengths and

weaknesses of each technique. To accomplish this, the project team built a set of soil-filled enclosures

and emplaced utility pipes of varied types, depths, and diameters in different soil conditions and burial 

configurations. NDE technologies from the four geophysical domains were tested to determine their

baseline characteristics in the soil enclosures. GPR was found to be the most effective of all the methods 

tested in this (test bed) environment because it was successfully able to locate both polyvinyl chloride 

(PVC) and metallic pipes down to a 6-ft depth. 

The last phase of the project included real-world field tests of five NDE technologies at sites having 

well-documented locations of buried utilities with different material types and emplacement conditions. 

The results showed GPR remains the most reliable and consistent NDE method available for the buried 

utility application. MASW proved to be an emerging NDE technology that successfully located buried 

utilities at one of the field sites. Frequency-domain EM sensors, passive pipe locators, and the acoustic

pipe locator failed to identify such targets reliably.

In summary, this comprehensive survey of existing and emerging NDE technologies identified stepped‐

frequency GPR and MASW as versatile and promising NDE technologies for detecting and locating 

buried utilities.

3 

CHAPTER 1. INTRODUCTION

Underground utilities represent fundamental assets in the infrastructure network of each city and

State, providing essential services, such as water, gas, sewage, telecommunications, and power, 

to their populations. The loss of such services due to outages can have significant and even fatal

consequences. Outages can occur due to integrity loss in the utility lines themselves or through 

unintended damage and disruption caused by construction activities. Infrastructure construction 

and renovation activities also necessitate the identification, characterization, and relocation of 

subsurface utility lines. Minimizing outages and service disruptions is a difficult task, especially

for highway agencies that may not have regular lines of communication established with local

utility providers. 

Furthermore, managing complex arrays of utility networks is challenging because underground 

utilities are often buried in public urban areas (roads, streets, etc.) without accurate metadata on 

the location, orientation, and types of underground utility lines present. In the absence of 

comprehensive utility location maps, traditional utility location methods rely on physical 

verification through time-consuming open-cuts practices (excavations, trenches, etc.) that

interfere with tightly scheduled project activities and can damage the underground utilities and

surrounding areas. As a result, the Federal Highway Administration (FHWA) has identified a 

critical need to investigate the availability, feasibility, and reliability of existing nondestructive 

evaluation (NDE) technologies to locate buried utilities and develop a comprehensive procedure

for deploying appropriate NDE systems for use in a variety of settings and configurations. 

FHWA has already engaged in multiple projects to address this need within the industry, 

assessing the effectiveness of certain NDE technologies and collecting significant feedback from

State departments of transportation (DOTs) on their utility location challenges and current

solutions. The Second Strategic Highway Research Program (SHRP 2) produced several reports 

that explored electromagnetic (EM), infrared, elastic, and other geophysical technologies for

their use in detecting, locating, and characterizing subsurface utilities (Sterling et al. 2009; 

Young and Kennedy 2015). This work provided a foundation on which to incorporate the current

and emerging technologies the NDE industry has to offer for utility location. 

The current project focused on existing technologies that have benefited from significant 

technological improvements since SHRP 2, such as the following: 

• Stepped-frequency ground-penetrating radar (GPR)—GPR is a geophysical NDE

technique that uses EM signals to detect and identify subsurface anomalies based on 

changes in electrical conductivity and relative dielectric properties of the subsurface 

layers. Stepped-frequency GPR has been developed in recent years to address these

challenges. Rather than relying on a single-frequency antenna, stepped-frequency GPR

systems combine an array of multiple smaller antennas that sweep through a wide

frequency range to provide an effective balance of depth and precision in measurement of 

subsurface features (Metje et al. 2007). While stepped-frequency GPR has been improved 

significantly and developed into a commercial product during the last two decades, 

availability and affordability of vehicle-mounted units have presented major roadblocks 

to adopting this technology. However, additional product suppliers have recently entered
4 

the market with competitively priced cart-based systems. Furthermore, recently

developed software enhancements supporting this technology now provide automated

analysis tools that require less extensive operator training to deploy stepped-frequency

GPR systems successfully. 

• Acoustic/elastic-wave techniques—A variety of seismic and acoustic methods exist to

detect and locate shallow subsurface features. Older techniques (active, passive, and

resonant sonics; seismic refraction/reflection) cannot provide the high subsurface 

resolution of GPR, but newer methods hold some promise for improved outcomes,

especially when combined with GPR surveys. For example, the multichannel analysis of 

surface waves (MASW) method generates cross-sectional, inverted shear images of the 

ground from surface waves propagated between an active seismic source and geophone 

receivers at predetermined offsets (Datta and Sarkar 2016; Hawari et al. 2017). Brand

new techniques, such as distributed acoustic sensing using fiber optic cables, may

eventually have a strong impact on the detection, location, and real-time monitoring of 

buried utilities (Hutchinson and Beird 2016; Khalil, Anukwu, and Nordin 2020). 

• Magnetic detection—This technique measures the anomalies in the Earth’s magnetic field

caused by buried metallic power cables as a means to locate them. It can be challenging 

to locate individual cables in the presence of superimposed magnetic fields or 

interferences from different cables buried in the same area. Conventional cable avoidance 

tool devices have been used successfully to locate buried power cables as long as there is

minimal interference from nearby cables and metallic utilities (Metje et al. 2007). 

• Frequency-domain electromagnetic (FDEM) method and time-domain electromagnetic

(TDEM) method—FDEM and TDEM represent two different technical approaches for

completing terrain conductivity surveys by using EM wavefields to detect differences in

average conductivity between utilities and surrounding soils to locate underground 

facilities. FDEM sweeps through a spectrum of frequencies to measure conductivity at a 

range of depths. TDEM uses a specialized periodic current to send out a single impulse

that allows for deeper scans of the terrain to be performed. TDEM tends to be robust in

the face of minor soil variations, while FDEM tends to be more sensitive with the 

capability to measure a feature depth based on the frequency sweep (Wightman et al.

2003). Terrain conductivity surveying is useful for utility detection in areas of high 

ambient conductivity (Anspach 1995). It can detect a wide range of metallic utilities, 

such as underground storage tanks, vault covers, wells, and other isolated metallic

utilities buried up to 16.4 ft deep (ASCE 2002). The performance of terrain conductivity 

imaging can be affected considerably by interfering magnetic fields produced along 

overhead power lines and by above-ground metal objects, such as vehicles, fences, or

buildings (Jeong and Abraham 2004), and the physical and chemical properties of the 

surrounding soils. TDEM was also used as part of a vehicle‐mounted system in the 2009 

SHRP 2 study. 

The project team evaluated several of these NDE technologies for their technical capabilities and

feasibility in addressing the buried utility location problem. 
5 

CHAPTER 2. CANDIDATE NDE TECHNOLOGIES TO DETECT AND LOCATE

BURIED UTILITIES

The following section summarizes a comprehensive literature review of promising NDE

technologies for buried utility detection and location. NDE technologies that rely on EM

wavefields to probe the subsurface, such as GPR and TDEM/FDEM, continue to be the most 

widely used for the buried utility application. Each technology exhibits both strengths and

limitations in survey cost and time that depend on the setting and other factors. In contrast,

seismic and acoustic technologies are not widely used for NDE utility detection. However, the 

open scientific literature indicates that seismic and acoustic methods can be combined 

successfully with GPR and EM methods to reduce location uncertainty. Furthermore, seismic

and acoustic technologies are particularly useful when GPR and EM surveys fail due to soil 

saturation, conductivity issues, physical surface obstructions, or pipe material. Table 1

summarizes the reviewed NDE technologies, including their advantages, automation potential, 

and related issues and limitations.

EM METHODS

GPR

GPR is a geophysical method developed for high-resolution investigations of Earth’s shallow 

subsurface and other structural systems. GPR operates by transmitting short pulses of EM energy

into a material using an antenna attached to a scanning system. The pulses reflect off dielectric

discontinuities in the material and are recorded by a receiving antenna. Reflection arrival times

and amplitudes relate directly to the location and nature of the dielectric discontinuities (e.g., 

air‐to-asphalt or asphalt-to-concrete, reinforcing steel, and underground utility). An oscilloscope 

displays the reflected energy captured by the GPR antenna as a series of pulses known as the 

“radar signal.” Each radar signal records the properties and thicknesses of the layers within the 

subsurface beneath the transmitting antenna. By combining multiple sampled signals from a 

moving survey into a single image, features within a structure can be identified.

Since the 1970s, applications of GPR have expanded to several areas, including the following: 

• Environmental and agricultural monitoring (Hubbard et al. 2005). 

• Sedimentary study (Neal 2004). 

• Forensic investigation (Hammon III, McMechan, and Zeng 2000). 

• Glacier monitoring (Hamran et al. 1997; Plewes and Hubbard 2001; Moorman and

Michel 2000; Hamran and Langley 2004). 

• Landmine detection (Daniels 2004; Langman and Inggs 1998; Scheers, Piette, and

Vander Vorst 1998). 

• Archaeological investigations (Sciotti et al. 2003). 

• Civil engineering (Grandjean, Gourry, and Bitri 2000; Xiaojian, Haizhong, and Huiliang 

1997). Lai, Dérobert, and Annan (2018) provide an extensive review of GPR studies to

document underground utilities.
6 

Figure 1 presents a vehicle-mounted GPR scan from this research study in which a buried object 

(utility pipe) was found. The utility pipe is indicated by the white-black-white patterned

hyperbola. GPR can be used for utility service location by identifying these EM boundaries 

between the soil and other media, such as gas or water pipes, cables, and different soils or voids. 

The strength and polarity of a GPR echo depend on several factors, including the absorption of 

the signal as it propagates to the target and back to the radar; the size, shape, and composition of 

the target; and the strength of the discontinuity at the reflecting boundary (Dolphin 1997). 

Source: FHWA. 

Figure 1. Image. Single GPR scan compiled by a survey vehicle identifying buried objects, 

which are indicated by the arrows pointed at the hyperbola. 

Single-Frequency Impulse GPR

Most GPR surveys use the single-frequency impulse GPR system described earlier in this 

section. Pulsed GPR techniques were developed starting in the 1930s to probe through ice, fresh 

water, salt deposits, desert sand, and rock formations. Impulse GPR systems have matured since 

the mid-1970s (Daniels 2004), and they are still of interest to many researchers due to their 

numerous advantages. Figure 2 presents a theoretical depiction of a traditional single-frequency 

impulse GPR antenna in operation on a concrete slab with two layers of steel reinforcement, 

where the resulting scan image is presented with the diagram. The scan image presents the 

typical hyperbola feature that correlates with pipe-like elements like rebar or utility pipes, where 

the presence of the top layer partially obscures the bottom layer. Although the impulse GPR is 

the most used system today, its noisy and inefficient receiver limits overall performance. Several 

advances have improved impulse GPR performance, including multiantenna (Yarovoy et al. 

2003; Manacorda et al. 2004), ultra‐short-pulse generator (Park et al. 2003; Park et al. 2004), and 

multiwaveform designs (Yarovoy et al. 2003; Park et al. 2003). These conventional GPR systems 

have been used worldwide for underground utility location problems (Jeng and Chen 2012; 

Metwaly 2015; Jaw and Hashim 2013). 

Buried Object
7 

Source: FHWA. 

Figure 2. Illustration. Plan view synthetic data presentation of GPR antenna traveling over 

concrete with steel reinforcement with B-scan GPR data presented in reference to the scan

location. 

Stepped-Frequency GPR Systems

Traditional single-frequency impulse GPR is limited in terms of widespread application and

adoption, primarily due to the tradeoff between high measurement precision and useful 

penetration depth (Kavi 2018). In recent years, stepped-frequency GPR systems have been

developed to address these challenges. Rather than relying on a single-frequency antenna,

stepped‐frequency systems use an array of multiple, smaller antennas used in various 

combinations to sweep through an entire range of frequencies to get an effective balance of depth 

and precision in measurement of subsurface features (Metje et al. 2007). Typical

stepped‐frequency antennas produce a series of impulse bursts across multiple frequencies

(typically 100 MHz–3.0 GHz) in a swept sine output fashion. The receiver measures the phase

and amplitude from each frequency transmitted to generate a time domain profile that can then 

be transferred to the frequency domain to generate a plot identifying amplitude reflections from

multiple depth layers. Additionally, because these antennas are operated in unison across

multiple frequency bands, multiple antennas are typically mounted simultaneously to collect data

across more than one single line scan, as performed with a single-frequency impulse GPR. This

technique allows for these antennas to be vehicle mounted and collect an entire lane’s worth of 

data in a single pass. Additionally, the antennas can be either air or ground coupled (figure 3).

While stepped-frequency GPR systems have advanced considerably and been developed into a 

commercial product during the last two decades, system availability and affordability have 

presented major historical roadblocks to adopting them as a viable NDE technology because the 

market lacked vendors selling the systems, and their price has not justified their use over 

traditional systems. However, more vendors have come to market with competitively priced
8 

systems that make stepped-frequency GPR much more logistically and fiscally viable for

organizations that have historically been unable to justify the expense. The software supporting 

this technology also provides additional tools for automated analysis, which means operators 

may not require extensive training for successful deployment of the system. 

Source: FHWA. 

Figure 3. Photo. Air-coupled, step-frequency GPR mounted on a vehicle for underground

utility location under roadway. 

Multichannel GPR Systems

Multichannel GPR systems use synchronized, single-channel, bi-static GPR antennas in various 

array layouts. Similar to multiantenna, stepped-frequency GPR systems, these arrays generally

are intended to be used for large-scale, mostly vehicle-mounted, data collection, but some can be 

uniquely customized to accommodate various project specifications. Multichannel GPR systems

have been used for two decades, but early systems did not deliver quality results due to the lack

of synchronization of the individual antenna responses. In the last 10 years, this asynchronous 

response has mostly been solved by technological advancements, and there is now a wider

acceptance of multichannel GPR systems in various industries. Deploying a multichannel GPR

system can be very effective in finding unknown utilities because it can reduce the survey time

significantly and provides high-density data capture with greater resolution. A case study 

conducted by the New York State DOT on the applications of GPR for highway pavements

showed the ability of multichannel GPR technology to detect and map buried utilities, indicating

the utility depths, orientations, and proximities to other surrounding infrastructure (Grivas 2006). 

Low-Frequency EM Instruments: Pipe and Cable Locators 

Finding a buried utility line is very similar in concept to radio detection: the utility line behaves

like a radio station that transmits a signal, and an underground utility locator is used to pick up 

this signal. This concept was first proposed, studied, and demonstrated by Gerhard Fisher owing 
9 

to his work on aircraft radio detection (Chemekoff and Toussaint 1994). With the technological 

advancement made in this field, a wide variety of underground utility locators now exist, among 

which are pipe and cable locators. This family of standard EM instruments is used to detect

magnetic fields around buried pipes and cables made of conductive materials. A pipe and cable

locator can be designed to work either in passive or active modes. In passive mode, the locator

listens to the background noise from the utility, and in active mode, the locator listens to a signal 

introduced into the utility using a transmitter. The transmission involves using coils that create

and release EM currents that propagate in the ground and generate magnetic fields around 

conductive materials. 

The magnetic fields induced can be sensed by an EM receiver located on the surface of the

ground. For better active detection performance, it is recommended that the transmitter be in the 

same orientation of the utility. This positioning can be achieved by trial and error. Once the 

magnetic fields are received, the signals recorded are processed, analyzed, and interpreted to

produce and visualize the results indicating the horizontal location of the subsurface utility. The

signal produced by the transmitter can be sent through the utility by either conductive means

through a direct connection, such as alligator clips, or by inductive means, where the signal is

introduced directly onto the metallic utility line using an induction clamp that is secured or

clamped around the utility line but does not connect metal to metal as the conductive alligator

clip does. The inductive method is great when the utility is not accessible, but the direct

(conductive) method is far more reliable because it is less prone to signal distortion and

interference from neighboring utilities. 

With ideal soil conditions, the effective locating depth of the direct method is about 9.8 ft, but 

this depth reduces considerably in dry sand and alkaline and high iron-content soils (Jeong and

Abraham 2004). The method works well with aluminum, steel pipes, copper, and other metallic

utilities that are buried with tracing materials above the utility itself but does not work on 

nonconductive utilities, such as those made of cast iron. This obstacle can, however, be easily

overcome in many cases. For example, in the case a nonconductive pipe is accessible, an

insulated trace wire connected to the transmitter can be fished through the pipe. The receiver is

then waved close to where the pipe is buried to mark its horizontal location. 

Pipe and cable locating instruments use a small yet crucial range of the EM spectrum, with

frequencies ranging from about 50 KHz to 480 KHz (ASCE 2002). The instruments can either be

single-frequency devices or multifrequency devices, where both have advantages and limitations.

FDEM Method: Terrain Conductivity Method

Terrain conductivity surveying is an EM technique that uses the differences in average

conductivity between utilities and surrounding soils to locate underground facilities. The

technique is based on the principles of eddy currents. A transmitter coil connected to an

alternating current (AC) source emits a primary magnetic field that produces induced secondary

currents known as eddy currents into the earth directly below the coil. The induced currents flow

to the surface with slightly different properties when they encounter a buried object with

conductivity different from the surrounding soil. A receiver at the ground uses the differences

between the emitted and induced currents to detect underground utilities. For instance, a buried
10 

metallic object has a lower conductivity than the soil surrounding it. Therefore, the induced 

currents have a different value than the currents emitted.

Terrain conductivity surveying is useful for utility detection in areas of high ambient

conductivity (Anspach 1995). It can detect a wide range of metallic utilities such as underground 

storage tanks, vault covers, wells, and other isolated metallic utilities buried up to 16.4 ft deep

(ASCE 2002). Under some conditions, the technique can be used as well to detect large, 

nonmetallic utilities such as water pipes in dry soils and empty and dry pipes in wet soils (ASCE 

2002). The performance of terrain conductivity imaging can be affected considerably by 

interfering magnetic fields noise produced along overhead power lines and aboveground metal

objects, such as vehicles, fences, or buildings (Jeong and Abraham 2004), and by the physical 

and chemical properties of the surrounding soils. The conductivity of a soil depends significantly

on the size of its particles: the smaller the particles are in the surrounding soil, the higher the 

conductivity is since fine-grained soils transmit the EM currents in easier and more direct wave

paths. In the previous SHRP 2 study (Young and Kennedy 2015), TDEM, the complementary

approach to FDEM, was evaluated as part of a vehicle-mounted system where a novel 

multitransmitter instrument was deployed. The present study sought to evaluate the capabilities

of FDEM because this method has the potential to determine the depth of a buried utility as a 

function of the frequency at which the utility is detected.

MAGNETIC METHODS

The Earth behaves like a large magnet, and its magnetic field is typically represented with lines

much like it is for a common magnet. So, at every point on and below the surface of the Earth, 

there is a level of magnetic field present. Objects made of certain materials, such as iron, steel,

and ferromagnetic alloys, are affected by this field in such a way that they develop their own

magnetic field very similar to that of a magnet. By contrast, buried objects made of nonmagnetic 

metals, such as aluminum, copper, and gold, are not affected by the Earth’s magnetic field and

therefore cannot be detected by magnetic locators. 

The most basic magnetic field sensor is a search coil or antenna, which consists of a coil of wire

wrapped around ferrite rods. When an alternating magnetic field cuts through the search coil, a 

voltage proportional to the strength of the magnetic field is produced. Generally, search coils are

arranged in triplet clusters, one for each of the Cartesian axes. In this way, a three-dimensional 

(3D) vector of the magnetic field can be generated for any point in space.

Magnetic Locators

Magnetic locators operate on the principle of detecting the difference in the magnetic field

present at two sensors spaced a fixed distance apart. In the absence of a buried object, the field at

both sensors is the same. The presence of an object made of iron or steel results in a difference

between the magnetic field at the top and the bottom sensors. That difference is called a gradient.

Magnetic locators indicate the detection of a gradient by changing the pitch of an audio tone and, 

depending on the model, with a bar graph on a visual display. The size of the buried object has

an impact on the size of the magnetic field difference or gradient. Likewise, the orientation of the 

buried object also affects the size of the gradient detected. The same object oriented vertically

will generally produce a larger difference. Some locators also indicate polarity, which can be 
11 

useful in determining whether the target is oriented vertically or horizontally. This is

accomplished by observing the polarity change at each end. The fixed spacing between the 

sensors determines the overall length of a locator. It has an impact on the field difference

detected or the sensitivity of the locator. The farther apart the sensors are, the more sensitive the 

locator becomes. 

Magnetometers

Ferrous metal or magnetic locators, commonly referred to as magnetometers, have long been

employed by both geophysicists and archaeologists for detecting underground objects and rock

formations. They detect variations in the Earth’s magnetic field as a result of underground 

features such as metallic pipes, underground storage tanks, or ore bodies. Consequently, only 

objects containing iron can be detected, thereby greatly limiting its value as a general technique 

for locating and identifying buried pipelines. The quality of results can also be affected by 

nearby buildings, cables, fences, and other metallic objects (Vickridge and Leontidis 1997), and

it is, therefore, a technique that should be used with care and in conjunction with other devices.

Several types of magnetometers are in use, but the most common are the fluxgate magnetometers

and the proton precession magnetometers. The fluxgate magnetometer is a device that measures

the intensity and orientation of magnetic lines of flux in three orthogonal directions (Telford, 

Geldart, and Sheriff 1990). Fluxgate magnetometers have been used in many applications, such

as geological prospecting, underground detection, aerospace navigation, underwater navigation, 

land navigation, and submarine detection. The heart of the fluxgate magnetometer is a 

ferromagnetic core surrounded by two coils of wire in a configuration resembling a transformer.

AC is passed through one coil, called the primary, producing an alternating magnetic field that

induces AC in the other coil, called the secondary. The intensity and phase of the AC in the 

secondary are constantly measured. When a change occurs in the external magnetic field, the 

output of the secondary coil changes. The extent and phase of this change can be analyzed to

determine the intensity and orientation of the flux lines.

The proton precession magnetometer is the most commonly used instrument for measuring the 

Earth’s magnetic field (Talwani and Kessinger 2003). In its simplest form, the instrument 

consists of a bottle filled with water. A strong electric current is passed for a few seconds 

through a coil wound around the bottle. Water is a paramagnetic substance and can be thought of 

as containing an assemblage of tiny magnets that execute random, thermally induced motions. 

When the current is turned off, the coil is used to record the current now produced by the tiny

magnets as they process around the direction of the Earth’s ambient magnetic field. The

frequency of precession is proportional to the Earth’s field and is conveniently recorded by 

digital counters, and thus the value of the magnetic field can be obtained. 

SEISMIC AND ACOUSTIC METHODS

Acoustic and seismic methods to detect underground utilities are especially useful in situations

when GPR and EM fail due to soil properties, conductivity issues, or electrical noise (Miller et 

al. 2000). These common obstacles seen with EM methods have no effect on the generation of 

acoustic and seismic waves. Additionally, EM methods depend on a discrepancy in the 

conductivity or permittivity between the buried pipes and the surrounding medium, which makes
12 

EM unusable for some targets, such as plastic, water-filled pipes (Papandreou, Rustighi, and 

Brennan 2008). The following sections review NDE methods that use seismic and/or acoustic

waves to interrogate the subsurface; describe their use, advantages, and limitations; and

recommend promising methods for further investigation. 

Traditional Acoustic Methods

Research to understand the behavior of acoustic waves in buried pipelines is extensive. Acoustic‐

wave methods divide into two types depending on whether there is direct access to a pipeline. 

Multiple acoustic techniques rely on access to a pipeline, e.g., a hydrant or manhole, to attach an

acoustic source. With access to the pipe, there are three main ways to generate acoustic waves:

active sonics, which measures sound waves in a pipe caused by striking it at an exposed point, 

passive sonics, which measures the vibrations associated with leaks escaping from pressurized

buried pipes, and resonant sonics, which depends on the contents of the pipe being a 

noncompressible fluid and generating a pressure wave in the fluid to detect pipe vibrations 

(Jeong and Abraham 2004). 

A traditional acoustic transmission method, an acoustic pipe locator (APL), requires an acoustic

generator and, typically, a single receiver in the form of a geophone or headphones. The concept

behind the method is regions with more intense signals correlate better to the buried pipe 

locations. Liu et al. (2020) determined that a frequency range from 50 to 150 Hz is most 

effective for pipe detection, although it is dependent on soil type. Detection results are prone to

interference from noise and distortion from surrounding medium properties, and interpretation of 

the results relies heavily on the user (Sterling et al. 2009). 

Seismic Methods

Similar to acoustic technologies, seismic waves remain unaffected by wet soil conditions and

conductivity issues. Specifically, analyzing seismic surface waves is advantageous because they

are relatively large in amplitude, which can provide ideal signal-to-noise ratios in areas with

elevated levels of mechanical or acoustic noise. During the SHRP 2 study, the use of a prototype 

seismic shear wave reflection imaging system was demonstrated, which is field and data

processing intensive (Young and Kennedy 2015). For this effort, the benefits and disadvantages 

of three seismic surface-wave methods were demonstrated: spectral analysis of surface waves

(SASW), MASW, and horizontal-to-vertical spectral ratio (HVSR). One or a combination of 

these methods may be useful in various situations to support EM recordings or used in

substitution when EM technologies are not effective (e.g., loose soil, nonconductive materials, or 

physical obstacles).

SASW

SASW leverages the dispersive characteristic of Rayleigh waves in an inhomogeneous medium 

(Fernández, Hermanns et al. 2011). As an active source method, surface waves are generated by 

dynamic sources, such as hammers, weight drops, vibroseis, and bulldozers, at a variety of

frequencies. SASW is ideal for measuring shear wave velocity with depth through inversion of 

dispersion curves (Badsar et al. 2010). This method can be applied to both bare and paved

surfaces, is ideal for depths up to 147.6 ft, and is not limited by soil type. 
13 

Minimum requirements for SASW are two receivers (geophones or accelerometers) at known 

offsets and one source. Accelerometers are useful for high-frequency studies at shallow depths 

on stiff surfaces like pavement, and geophones are ideal for lower frequency studies deeper in

soils (Al-Shayea, Woods, and Gilmore 1994). The accessible area on the surface needs to be 

equal to or greater than the depth required, which is an easy requirement for shallow-buried 

utilities (GEOVision 2016). Multiple dispersive layers indicate the presence of stiffer materials

that may coincide with buried objects. 

MASW

Conventional SASW is limited by multiple factors, including phase unwrapping errors,

inefficient data filtering, and failure to classify multiple modes (Lin, Lin, and Chien 2017). 

Unlike the two-channel SASW method, MASW implements a two-dimensional (2D) wavefield

transformation to produce images of subsurface shear-wave velocity (Park, Miller, and Xia 1996; 

Xia et al. 1998; Park, Miller, and Xia 1999; Xia, Miller, and Park 1999; Lin, Lin, and Chien 

2017). Utilizing surface-wave energy between 1 and 30 Hz on multiple channels (minimum of 

24 geophones), MASW generates surface waves using an active (sledgehammer) or passive 

(traffic, tidal motions, thunder) source (Park et al. 2007). For shallower studies, an active source 

is ideal as it images objects at depths less than 98.4 ft. 

By exploiting the dispersion of surface waves through pits, trenches, or buried utilities compared 

to the surrounding medium, MASW software can locate localized zones of subsurface anomalies, 

including pipes. As an example, one utility software package generates a shear velocity (Vs) 

profile through dispersion-curve analysis from a multichannel record and then an inversion 

process (Park et al. 2000). Miller et al. (2000) combined MASW with a common middle point 

data acquisition to delineate vertical and horizontal variations in subsurface materials. 

HVSR

HVSR may be performed in conjunction with MASW as a straightforward, passive seismic

method for subsurface mapping (Mendecki, Bieta, and Mycka 2014; Sauret et al. 2015). Khalil, 

Anukwu, and Nordin (2020) successfully applied the HVSR technique to mapping underground 

utilities by exploiting the higher velocities in utilities compared to that of the soil. This

discrepancy generates an impedance contrast between the utility and the subsurface layers

because their densities and velocities differ. HVSR methodology is commonly used in the United

States for soil resonance and site response studies, but there are no available case studies of the 

technique applied to underground utilities. Given the success of Khalil, Anukwu, and Nordin 

(2020) in Malaysia, their methodology could be applied to buried pipe and utilities detection in

the United States. Figure 4 shows the pseudo 3D HVSR section they generated from multiple 

geophones. The depth (z-axis) was obtained by converting from the frequency domain to the 

depth domain. Dashed and solid lines represent the trend of possible subsurface utilities. 
14 

© 2020 Elsevier Science & Technology Journals(see Acknowledgments section). 

Figure 4. Image. Pseudo 3D HVSR section generated from multiple geophones (Khalil, 

Anukwu, and Nordin 2020). 

SUMMARY

Table 1 presents a summary of the key advantages, limitations, and other technical details 

surrounding the technologies reviewed in this section. 
15 

Table 1. Summary of researched NDE technologies. 

NDE Technology Advantages Limitations Automation 

Capabilities Other Issues

GPR technologies •Most utility 

types detected 

(including 

plastic, 

nonmetallic, and 

metal). 

•Wide market 

availability and 

efficient power 

usage. 

•Highest available 

spatial resolution 

under favorable 

conditions. 

•Highly sensitive 

to soil type and 

utility electrical 

conductivity. 

•Signal scatters in 

heterogeneous 

subsurface 

conditions. 

•Suffers in 

presence of 

nearby 

conductive 

materials. 

•Automated data 

acquisition and 

processing 

available. 

•High-quality 

image 

visualizations in 

3D.

•Requires 

significant 

analyst training 

for accurate 

feature 

interpretation. 

Magnetic locator 

technology

•Measures 

intensity of 

buried 

ferromagnetic 

materials 

(manmade 

objects 

containing iron 

or steel). 

•Detects 

underground 

storage tanks and 

buried manhole 

covers. 

•Detects buried 

military 

ordnance. 

•Sensitive to 

environmental 

factors (induced 

magnetic fields). 

•Limited 

bandwidth. 

•Sensitive to 

interference. 

•Automated 

features 

available (gain, 

depth readings, 

etc.). 

•Fields induced in 

reinforcements 

in pavement 

above utility 

destroy detection 

capabilities. 

EM technologies:

Pipe and cable locators

•Detects buried 

copper, 

aluminum, and 

steel objects. 

•Precise location 

capabilities even 

in the presence 

of signal 

distortion. 

•Already widely 

used in 

subsurface utility 

tracking.

•Sensitive to 

cable and pipe 

diameters and 

types. 

•Sensitive to soil 

conditions. 

•Performance 

degrades in 

proximity to 

nearby 

conductors. 

•Automated 

features 

available (gain, 

depth readings, 

etc.). 

•Field distortion 

(asymmetrical 

EM fields) can 

occur in 

complicated, 

multiconductor 

underground 

topologies. 
16 

NDE Technology Advantages Limitations Automation 

Capabilities Other Issues

EM technologies: 

Terrain conductivity 

method

•Detects wide 

range of utilities. 

•Moderately 

inexpensive. 

•Useful in areas 

with nonutility 

congestion or 

high ambient 

conductivity. 

•Moderate-topoor accuracy. 

•Sensitive to 

instrument and 

subsurface noise. 

•Subject to 

unexpected 

spikes (extreme 

conductivity 

values). 

•Sensitive to 

wave 

attenuation.

•Automated data 

acquisition, 

conditioning, 

and processing 

available. 

•Fields induced in 

reinforcements 

in pavement 

above utility 

destroy detection 

capabilities. 

Acoustic technologies:

APL

•Identifies metal, 

PVC, concrete, 

and clay 

underground 

targets. Not 

limited by pipe 

conductivity or 

soft soil. 

•Ideal for shallow 

targets (12–

96 inches below 

surface).

•Detection and 

approximate 

locations only. 

•Minimum target 

size of 0.5 inches 

required; poor 

depth resolution. 

•Real-time data 

visualization 

available. 

•Underdeveloped 

for the utility 

detection and 

location 

application. 

Seismic technologies:

MASW

•Not limited by 

pipe conductivity 

or soft soil. 

Identifies plastic 

and metal targets 

under grass and 

pavement. 

•Ideal for shallow 

targets (12–

96 inches below 

surface).

•Moderate depth 

precision 

(+/- 15 percent). 

•Requires slower 

data acquisition 

and 

multigeophone 

array. 

•Multiple dataprocessing 

software 

packages 

available. 

•Data-processing 

improvements 

still needed prior 

to commercial 

implementation. 

Seismic technologies:

HVSR

•Not limited by 

pipe conductivity 

or soft soil. 

Identifies plastic 

and metal targets 

under grass and 

pavement. 

•Ideal for shallow 

targets (12–

96 inches below 

surface). 

•Moderate depth 

precision 

(+/- 10 percent). 

•Requires threecomponent 

geophones. 

•None. •Less well 

developed and 

tested than other 

NDE techniques 

for utility 

detection and 

location. 

•Could be 

performed 

concurrently 

with MASW to 

improve 

outcomes.

PVC = polyvinyl chloride. 
17 

CHAPTER 3. STATE DOT IMPLEMENTATION

Two key objectives of this study were to understand how State DOTs currently use NDE

technologies to detect and locate buried utilities and to recommend emerging techniques that

merit implementation. The implementation assistance program that followed the SHRP 2 R06D 

study allowed multiple States to use NDE technologies. FHWA requested an update on the 

extent to which State DOTs have used these technologies successfully to identify underground 

utilities in both existing and new construction. 

To determine the current usage of NDE technologies, the project team performed a limited

survey (polling) of nine State DOTs (California, Florida, Kentucky, Louisiana, Minnesota, 

Missouri, Oregon, Texas, and Virginia) to document their practices and concerns and to 

determine whether they used in-house or hired services for underground utility location, the 

types of technologies they typically used, and the advantages and limitations of those use cases.

All results are available on request. Figure 5, figure 6, figure 7, figure 8, and figure 9 present

summarized results of the survey. 

Source: FHWA. 

Figure 5. Chart. Survey response from DOTs regarding internal and external use of NDE

technologies. 

In figure 5, the striped pattern represents “We deploy NDE technologies for field data collection

and perform the analysis and reporting internally.” The dotted pattern represents “We deploy 

NDE technologies for field data collection and use an outside organization for analysis and

reporting.” The solid pattern represents “We use an outside organization for NDE field data

collection, analysis, and reporting.” 

Which of the following best describes your deployment of NDE technologies for utility location services?
18 

Source: FHWA. 

Figure 6. Graph. Survey response regarding types of NDE technologies used.

Source: FHWA. 

Figure 7. Graph. Survey response on which types of NDE technologies are reliable to

inform engineering and construction judgments. 

Which of the following has your organization (or relevant 

subcontractors) used to perform utility location services? 

Which of the following would your organization consider to be reliable to 

inform engineering and construction judgments? 
19 

Source: FHWA. 

Figure 8. Graph. Survey response on influence factors on adopting new NDE technologies

for utility location. 

1

0

1

1

0

0

1

1

0

2

3

2

5

4

0

2

0

7

5

6

4

6

8

8

7

0

0

0

2

1

1

0

0

2

2

2

0

0

1

0

0 2 4 6 8 10 12

Precision/Accuracy of NDE technology

Cost of equipment/software

Cost/difficulty of training technicians

Cost/difficulty of training analysts

Speed of field data collection

Speed of data analysis reporting

Commercial availability

Data management tools

What influence do these factors have on the decision to adopt a new NDE 

technology for utility location services?

No Influence Minor Influence Major Influence Critical Influence N/A
20 

Source: FHWA. 

Figure 9. Graph. Survey response regarding the ranking of improvements needed for the

implementation and/or application of NDE technologies for utility location services.

Surveys of staff members in nine DOT offices revealed several points: GPR is the most 

commonly used technique for utility detection, followed by traditional magnetic line locators and 

TDEM induction. Seismic and acoustic techniques are underutilized to detect buried utilities. 

High interest exists in automating data collection and data processing. More guidance on best

practices in various environments would be used by DOTs, and accurate location readings from

NDE technologies are the most important aspect to DOT personnel. 

The State DOT survey responses helped prioritize the lab and field experiments. The project

team had not considered TDEM/FDEM methods in the early study; however, based on feedback

and interest from DOT personnel and FHWA, the field tests included FDEM. The NDE

technologies selected for lab and field experiments included GPR, TDEM/FDEM,

MASW/HVSR, and APL methods. All methods have strong imaging capabilities at shallow 

depths, do not require access to a pipeline, and can be used in conjunction with one another to

improve outcomes and decrease uncertainty. Additionally, most of the data-collection hardware

and protocols for the selected methods were already available in the commercial market.

3

4

0

0

0

0

1

4

5

0

2

0

3

0

1

0

1

3

2

4

0

1

0

0

0

0

1

3

4

3

0

0

2

0

5

1

0

2

1

0

0

0

1

3

2

1

4

0

0

3

0

0

1

3

3

1

0

1

0

0

1

1

1

6

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Further research and

development of better

NDE methods

Development of automated

field data collection systems

(robotics)

Development of analysis

software for non-technical

users

Training courses and

materials for field

data collection

Development of automated

data analysis protocols

Training courses and materials

for data analysis and reporting

Development of data

management and

integration tools

I don't have experience

with these technologies

Please rank the following with respect to improving the implementation/application of 

NDE technology for utility location services.

1st Choice 2nd Choice 3rd Choice 4th Choice 5th Choice 6th Choice 7th Choice 8th Choice
21 

CHAPTER 4. CONTROLLED LAB AND FIELD EXPERIMENTS

While the literature search and industry review yielded important findings on the state and

availability of modern NDE technologies for locating buried utilities, the next important step in

this study was evaluating these technologies side-by-side to determine their efficacy in equal test

conditions. GPR, FDEM, MASW, HVSR, and APL were the methods selected for evaluation

during this part of the project. They were chosen for their ability to be used on grade without the 

need for utility exposure, their relevant equipment and systems being readily available in the 

market for use, and the existence of established procedures and processes for their deployment. 

The point on availability was particularly important here as many of the techniques reviewed in

the literature were demonstrated to be viable in theory but are not ready for testing in practice

such that State DOTs would ultimately be able to deploy them if they are found to be effective in

utility location. 

The project team developed a laboratory testing plan to thoroughly evaluate the different selected

NDE technologies. A matrix of specimens was designed and tested, for which typical utility

pipes of varying sizes were buried in different soil conditions and burial configurations to assess

the effectiveness of each NDE technology in a controlled setting. A combination of soil-filled

enclosures was designed, built, and tested under different controlled configurations. Four 

specimen types were investigated: fine-grained cohesive soil, coarse-grained cohesionless soil, 

two layers of cohesive soils at the bottom and cohesionless soil on top, and two layers of 

cohesionless soil at the bottom and cohesive soil on top. 

The laboratory specimens were designed and built at a North Carolina DOT indoor facility. The

specimens consisted of soil-filled enclosures made of raised garden beds stacked on top of each

other. Each raised bed consisted of a wooden frame measuring 12 ft × 5 ft × 1 ft, with a total of 

six beds being added incrementally as scans were completed over the embedded utility pipes. 

The incremental addition of each bed was referred to as a lift. Figure 10, figure 11, figure 12, and

figure 13 present diagrams of the stacked beds for the cohesive soil, cohesionless soil, and mixed

soil type of specimens, while figure 14 presents an image of the specimens under construction. 
22 

Source: FHWA. 

Figure 10. Illustration. Soil box specimen with six total beds of cohesive soil stacked

together. 

Source: FHWA. 

Figure 11. Illustration. Soil box specimen with six total beds of cohesionless soil stacked

together. 
23 

Source: FHWA. 

Figure 12. Illustration. Soil box specimen with six total beds of cohesive and cohesionless

soil stacked together.

Source: FHWA. 

Figure 13. Illustration. Soil box specimen with six total beds of cohesionless and cohesive 

soil stacked together.
24 

Source: FHWA. 

Figure 14. Photo. First level of soil box specimens with buried utilities in parallel. 

TEST METHODS AND INSTRUMENTATION

Stepped-Frequency GPR Field Plan and Results

The GPR instrument used for field testing featured unique stepped-frequency, continuous-wave

radar technology that provides a frequency range of 200–3,440 MHz. This range of frequencies

means that the high-precision measurements associated with high-frequency signals can be 

captured at the same time as the high-penetration depth measurements associated with lowfrequency signals. Scans were taken on each type of soil box at each lift level, with the 

instrument being pushed along the soil transverse to the orientation of the buried targets. 

Figure 15 presents an image of the GPR system in use on a given soil box. 

Source: FHWA. 

Figure 15. Photo. GPR system with integrated cart scanning soil box. 
25 

The scans gathered using the GPR were analyzed by reviewing them for the signature hyperbolic 

peaks that are produced by subsurface targets, as presented in figure 16, figure 17, figure 18, and

figure 19. These peaks were tracked across each test lift for the four specimen types to identify

the depth at which the feature was no longer visible. Table 2 summarizes these findings for each

pipe and specimen type, respectively.

Source: FHWA. 

Figure 16. Image. GPR scans collected on cohesive soil test specimen, where each of the

hyperbolic peaks represents a buried utility observed in the data. 

Source: FHWA. 

Figure 17. Image. GPR scans collected on cohesionless soil test specimen, where each of the

hyperbolic peaks represents a buried utility observed in the data. 
26 

Source: FHWA. 

Figure 18. Image. GPR scans collected on cohesive-cohesionless soil test specimen, where

each of the hyperbolic peaks represents a buried utility observed in the data. 

Source: FHWA. 

Figure 19. Image. GPR scans collected on cohesionless-cohesive soil test specimen, where

each of the hyperbolic peaks represents a buried utility observed in the data. 
27 

Table 2. Summary of maximum observable lift allowing visualization of subsurface target

with GPR. 

Maximum Observable

Lift

Specimen

1

Specimen

2

Specimen

3

Specimen

4

Concrete pipe 0 0 0* 0*

Fiber optic cable 0 0 0* 0*

1-inch Copper pipe 5 6 4* 6*

2-inch Steel pipe 5 6 6* 6*

4-inch Steel pipe 6 6 6* 6*

6-inch Steel pipe 6 6 6* 6*

6-inch PVC pipe 4 5 6* 6*

4-inch PVC pipe 4 5 0* 0*

2-inch PVC pipe 3 5 0* 0*

Insulated copper wire 2 5 0* 0*

*Tests only completed for top lifts 4–6. 

Pipe and Cable Locators Field Plan and Results

The project team used an underground utilities locator instrument to perform pipe and cable

locations. The system allows for the use of a passive detection mode and an active detection

mode where a signal can be injected into a given conductive material to track its position 

underground. Scanning with the instrument was performed manually, with a systematic approach

being taken to cover the entire soil box and detect the subsurface targets according to the 

instructions in the instrument documentation. This instrument was used on every box and at

every lift under investigation. An image of it in operation is shown in figure 20. 

In passive operation mode, the instrument was unable to locate any of the subsurface targets

using the advised method for its deployment. This failure included the steel and copper pipes that

were made of conductive materials. As a check on the equipment, the instrument was also

operated in its active mode, where a signal was injected into the conductive pipes to detect the 

target’s presence. This operation approach was successful for the copper pipe and every size of

the steel pipes to lift level 6 for each specimen.
28 

Source: FHWA. 

Figure 20. Photo. Underground utilities locator scanning over steel pipe. 

APL Field Plan and Results

The largest uncertainty with an APL is the presence of inhomogeneous soil, including air

pockets; however, under the controlled experiment setup, the field team was able to reduce this

cause of error by compacting the soil through manual tamping. Data collection was performed at

an interval of every 6 inches along the length of the soil boxes, with the instrument being 

operated in parallel with the orientation of the subsurface targets. Figure 21 presents an image of

the APL in use.

Analysis of the APL data involved a review of the acoustic response B-scans gathered during 

testing to identify the presence of any clear peaks. While peaks were identified in some scans

across the specimens and lifts, they generally did not align with the known lateral position of the 

subsurface targets, giving inconclusive results. It is possible that the limiting boundary 

conditions of the test specimens were ultimately not conducive to this test method, which is

typically used in unbounded conditions. 
29 

Source: FHWA. 

Figure 21. Photo. APL in operation. 

FDEM Instrument Field Plan and Results

The project team used a ground conductivity meter for FDEM measurements. Based on the 

documentation, the system was calibrated and nulled each day before testing. Data collection

was performed at an interval of every 6 inches along the length of the soil boxes, with the 

instrument being operated in parallel with the orientation of the subsurface targets (figure 22).

Analysis of the FDEM data involved a review of the collected relative conductivity values,

looking for significant local minimums that typically indicate the presence of a conductive pipe.

Figure 23 presents an example of an FDEM scan where two steel pipes are indicated by the two

significant negative peaks in the data. Table 3 summarizes the results of this test method. 

Source: FHWA. 

Figure 22. Photo. Ground conductivity meter in operation. 
30 

Source: FHWA. 

Figure 23. Graph. Example of FDEM scan with two steel pipes indicated by local 

minimums.

Table 3. Summary of maximum observable lift allowing visualization of subsurface target

with FDEM.

Maximum Observable

Lift

Specimen

1

Specimen

2

Specimen

3

Specimen

4

Concrete pipe 0 0 0* 0*

Fiber optic cable 0 0 0* 0*

1-inch Copper pipe 0 0 0* 0*

2-inch Steel pipe 2 2 0* 0*

4-inch Steel pipe 2 2 0* 0*

6-inch Steel pipe 2 2 0* 0*

6-inch PVC pipe 0 0 0* 0*

4-inch PVC pipe 0 0 0* 0*

2-inch PVC pipe 0 0 0* 0*

Insulated copper wire 0 0 0* 0*

*Tests only completed for lifts 4–6. 

HVSR Field Plan and Results

Using four broadband seismometers, the project team measured ambient noise for a 30-min

duration across at least two transects running perpendicular to the pipes for box 1, box 2, and box 

3 on one to two different lifts. The sensors were spaced so that every other sensor would be 

directly above a pipe (figure 24). The team was mainly interested in measurements on the two

homogenous boxes because of the time-consuming nature of the test and because soil 

composition is less likely to have an effect on HVSR analysis; however, they also ran two

30-min tests on the mixed soil box, box 3. They also conducted two calibration tests on the 

ground near the test site to calculate the site frequency. 

-600

-500

-400

-300

-200

-100

0

100

200

300

0 20 40 60 80 100 120 140 160

Relative Conductivity (mS/m)

Scan Position (in)
31 

Source: FHWA. 

Figure 24. Photo. HVSR four-sensor test setup for soil box 1, lift 4. 

The team used the HVInv code (García-Jerez et al. 2016) to model ambient seismic energy and

compute synthetic HVSR curves between 1 and 100 Hz in two models. The HVInv software

relies on the diffuse field assumption, which specifies that the ambient seismic wavefield is

composed of both shear and surface waves, unlike traditional HVSR methodology that assumes

negligible surface waves (Nakamura 1989). This approach to HVSR processing is relatively

straightforward, although different researchers use variations in the main methodology, which

depends on the target depth, achievable resolution, study area, etc. The team followed the 

methodology of Khalil, Anukwu, and Nordin (2020) and Thompson et al. (2012) with a few

adjustments due to the nature of the soil box and testing setup. 

The soil box HVSR data were too inconsistent to confirm the presence of any pipes (see

figure 25 for sample HVSR curves). The data inconsistency is likely related to the poor datacollection environment of the stacked testbed for ambient HVSR seismic measurements. The

SESAME experiment (European Commission 2004) notes that HVSR measurements should be 

obtained in a quiet setting, with no anthropogenic noise (footsteps, machinery). Furthermore, the 

only available study of HVSR for nondestructive detection of underground utilities was carried

out successfully in real-world conditions, not in a confined enclosure (the soil box walls) in close

proximity to the pipes. 
32 

 

Source: FHWA. 

A. HVSR plots for station 2 above the 6-ft steel pipe for box 1, lift 6. 

Source: FHWA. 

B. HVSR plots for station 2 above the 6-ft steel pipe for box 1, lift 4. 

 

Source: FHWA. 

C. HVSR plots for station 2 above the 6-ft steel pipe for box 2, lift 3. 

Figure 25. Graphs. HVSR plots to confirm the presence of any pipes. 
33 

In figure 25, the six-layer model suggests that the peak due to the impedance contrast between

the soil and steel should appear at approximately 32.5 Hz; however, the multiple frequency peaks

observed across different boxes and lifts are too variable to confirm the success of the HVSR test

in this experiment. Moreover, edge effects from the soil box are likely interfering with the 

results.

CONTROLLED LABORATORY CONCLUSIONS

The laboratory testing phase of the study indicated that GPR was the most effective EM method 

capable of identifying buried utilities. FDEM exhibited a limited ability to detect utilities, and the 

passive-mode magnetic pipe locator produced no meaningful results. While a concrete pipe and

fiber optic cable were not detected by any of the EM methods, GPR successfully found both 

polyvinyl chloride (PVC) and metallic targets down to depths of 4–6 ft. In contrast, the FDEM

system successfully imaged larger metallic targets down to a depth of 2 ft. The homogeneous soil 

boxes presented fewer challenges to the EM technologies than the heterogeneous soil boxes. 

The seismic and acoustic methods (MASW, HVSR, and APL, respectively) did not locate any

buried utilities during the laboratory testing, primarily because the test conditions favored the 

EM techniques. The small soil boxes constructed for the laboratory testing introduced strong 

boundary effects, which created poor conditions for measuring clear seismic/acoustic wavefields.

In addition, MASW/HVSR may have been confounded by the presence of high-frequency

vibrational noise produced by equipment in the testing area. The project team determined that

seismic and acoustic methods would be better suited to “boundary-free,” real-world conditions. 

35 

CHAPTER 5. FIELD EXPERIMENTS—VIRGINIA DOT SITES

Based on the results from the controlled and laboratory experiments, the team field-tested a 

variety of NDE technologies in southern Virginia. Virginia DOT (VDOT) identified field sites

with well-documented buried utilities and accessible locations for NDE technology tests. VDOT

provided a list of possible field sites with buried utilities that varied in material type (PVC versus

metal), diameter, and depth (shallow versus deep). The field team selected three VDOT‐

approved locations with similar sets of buried utilities, including PVC water and sewage pipes

from 1 to 10 ft below the ground surface. The neighborhoods referred to throughout the report

include Spring Hill (36.9323°N, -76.5898°E), Settlers Ridge (36.9391°N, -76.5060°E), and

Windsong Way (36.9535°N, -76.5406°E); all three sites are located near the town of Carrollton, 

VA. 

The team then evaluated the site locations and developed scan plans for the NDE tests after

onsite walks and analyses of traffic conditions. Figure 26, figure 27, and figure 28 present the 

site maps for Spring Hill, Settlers Ridge, and Windsong Way, with their respective utility types 

and locations denoted. 
36 

Original Photo: © 2021 Google® (see Acknowledgments section). Image modified by FHWA to identify utility

types and locations. 

FP = from plans.

Figure 26. Photo. Aerial view of the Spring Hill field site with utility locations, elevations, 

and type indicated with solid (sewer) or dashed (water) lines.
37 

Original Photo: © 2021 Google® (see Acknowledgments section). Image modified by FHWA to identify utility 

types and locations. 

Figure 27. Photo. Aerial view of the Settlers Ridge field test site with utility locations, 

elevations, and types indicated with solid (sewer) or dashed (water) lines.
38 

Original Photo: © 2021 Google® (see Acknowledgments section). Image modified by FHWA to identify utility 

types and locations. 

Figure 28. Photo. Aerial view of the Windsong Way field test site with utility locations, 

elevations, and types indicated with solid (sewer) or dashed (water) lines.

DATA ACQUISITION METHODS AND RESULTS

The field testing focused on four NDE technologies, including two EM techniques 

(stepped-frequency GPR and FDEM) and two seismic/acoustic techniques (MASW and APL).

The following subsections provide sensor information, field plans for data acquisition, and

results for GPR, MASW, APL, and FDEM ordered by their capabilities (from best to worst) to

detect the buried utilities at the three sites.

GPR Field Plan and Results

The laboratory testing used a pushcart-based, stepped-frequency GPR system that had just 

entered the commercial market. While this new system successfully captured features of the

buried utility pipes, the raw data were difficult to access and analyze. For field tests, the project

team and client elected to test another stepped-frequency GPR system and a dual‐frequency (DF) 

GPR system with similar detection principles to the laboratory-tested system. Both field-tested

systems produced data in an accessible format that made analysis straightforward.
39 

First, the project team tested a GPR system with a DF digital antenna. The DF antenna operates

simultaneously at two frequencies (300 and 800 MHz) to resolve buried utility locations. This

antenna design exploits the deeper signal‐penetration depth of the 300-MHz antenna and the 

more precise shallow feature localization of the 800-MHz antenna. In traditional applications, 

separate scans with each antenna would be needed to capture both datasets. The DF antenna 

system records two distinct signals in one scan, and the analysis software merges the scans into a 

final image that captures the full depth and precision from the separate frequencies.

A single technician operates the DF antenna using a four-wheeled pushcart and collects data

using software on a tablet connected to the antenna. Figure 29 shows an operator deploying a DF

antenna in the field. Compared to a vehicle-based or discrete point testing NDE acquisition

system, the DF antenna system is mobile enough to be deployed in a variety of field conditions. 

This mobility was critical for the field test locations, which included roads, sidewalks, grass, and

uneven ground. 

In a real-world setting, the location of a buried utility pipe is not known, and GPR scans must be 

performed in both transverse and longitudinal directions to locate buried objects. However, to

save acquisition time during the field-testing program, the team took GPR scans only in

directions perpendicular to the known utility pipe orientations at the three field sites.

Source: FHWA. 

Figure 29. Photo. GPR system with DF antenna.

The project team also deployed a stepped-frequency GPR system, which features a 

ground‐coupled antenna and multichannel data acquisition. The stepped-frequency system is

vehicle-based and typically deployed for roadway and bridge inspections. The system’s 
40 

ultra‐wideband frequency spectrum (200 MHz–3 GHz) makes it well-suited for buried utility

location. The stepped-frequency system permits high-speed data collection and can perform up 

to 28 data scans in parallel during a single pass over a location. However, the stepped-frequency

system cannot be used on uneven or irregular terrain and must be deployed on established

roadways. This limitation hampered the utility of the stepped-frequency system during the field

tests.

The stepped-frequency system also features a Global Positioning System (GPS)-based encoder

that tracks the location of the antenna as it scans a test location. For this field deployment, the 

team used a survey system (total station) to lock down the position of the antenna. The team also

leveraged the total station’s GPS tracking functionality to capture the antenna coordinates along 

its travel path. The stepped-frequency system scans at the three testing sites covered only the 

roadway paths available at each site and used antenna orientations aligned with the direction of 

travel on the roads. Figure 30 shows the stepped-frequency GPR system on its travel vehicle

along with the total station. 

Source: FHWA. 

Figure 30. Photos. Photo on left shows a stepped-frequency GPR system mounted on a 

travel vehicle, and photo on right shows a total station surveying system used to track the

GPR antenna positions. 

Analysts examined the scans from the two GPR systems to look for the distinctive time domain 

hyperbolic peaks produced by subsurface targets in response to radar pulses (figure 31). Each

scan’s observed features, GPS-encoded positions, and other field measurements were compared
41 

to the documented locations of buried utilities to determine whether the GPR systems

successfully detected the targets. Figure 31 shows an example of the interpreted results from a 

DF antenna GPR system scan, with yellow boxes outlining the detected utilities. The 800-MHz

channel found a shallow target with high resolution, and the 300-MHz channel scan revealed two

lower‐resolution targets near 3 and 7 ft below the surface. The system’s DF antennas collect two 

data channels that are displayed on separate depth-of-penetration axes. The boxes indicate 

features classified as buried utility pipes according to VDOT documentation. 

Because the field testing involved two GPR systems with different positioning systems, the data

from each test were analyzed and aggregated separately. Table 4 summarizes the DF antenna 

GPR system results for each scan line. 

Source: FHWA. 

Figure 31. Image. Example of the DF antenna GPR scan collected during field testing at 

Spring Hill (scan line identification 2 in table 4). 
42 

Table 4. Scan line metadata and respective utility targets for the DF antenna GPR tests,

including the system’s success or failure to detect targets.

Scan

Line

ID

Location Date Primary

Target

Primary

Depth

(ft)

Primary

Target

Detected?

Secondary

Target

Secondary

Depth (ft)

Secondary

Target

Detected?

2 Spring Hill 8/24/2021 PVC

water 3 Yes PVC sewer 7 Yes

3 Spring Hill 8/24/2021 PVC

water 3 Yes PVC sewer 7 No

4 Spring Hill 8/24/2021 PVC

water 3 Yes PVC sewer 7 Yes

5 Spring Hill 8/24/2021 PVC

water 3 No PVC sewer 7 No

6 Spring Hill 8/24/2021 PVC

water 3 No NA NA NA

7 Spring Hill 8/24/2021 PVC

water 3 Yes PVC sewer 9 No

8 Spring Hill 8/24/2021 PVC

water 3 No PVC sewer 9 Yes

1 Settlers

Ridge 8/25/2021 Copperwater 4 No NA NA NA

3 Settlers

Ridge 8/25/2021 Copperwater 4 Yes PVC sewer 7 No

4 Settlers

Ridge 8/25/2021 PVCwater 4 No NA NA NA

6 Settlers

Ridge 8/25/2021 PVCwater 4 Yes PVC sewer 7 Yes

7 Settlers

Ridge 8/25/2021 PVCwater 3 Yes PVC sewer 8 No

3 Windsong

Way 8/26/2021 Copperwater 3 Yes PVC sewer 9.5 No

4 Windsong

Way 8/26/2021 PVCwater 3 Yes PVC sewer 9.5 No

5 Windsong

Way 8/26/2021 PVCwater 3 Yes PVC sewer 9 No

NA = Not applicable. 

Several general observations can be made about the performance of the DF antenna GPR system

at the three field sites. First, the system performed GPR scans in nonideal environments with

variable and uneven surface conditions without a reduction in data quality or system

performance. Second, the DF antenna GPR is easy to operate—a single technician can push both 

the antenna cart along a scan line and review data in realtime. Third, the DF antenna feature

produces two channels of output at different frequencies, which provides better resolution of 

subsurface features. For instance, the DF antenna GPR system detected PVC water lines at

relatively shallow depths, despite the nonconductive material type. However, it did not detect

PVC water lines at relatively deep depths. This result is likely due to both the increased depth of 

pipe and the nonconductive pipe material type. 

In general, the stepped-frequency GPR system did not perform as well as the DF antenna GPR

system. While the stepped-frequency GPR is deployable in high-traffic settings and at typical

roadway speeds, it requires considerable setup and tuning to ensure high-quality data collection.
43 

The system benefits from GPS data encoding, which is an advantage over the DF antenna GPR, 

because it minimizes the need for handwritten field notes on scan start/stop positioning. The

stepped-frequency GPR also detected PVC water lines at relatively shallow depths despite the 

nonconductive material type, but it did not detect the deeper PVC water lines due to

nonconductive pipe material and the increased depth of the utility lines. Figure 32 presents an 

example of the stepped-frequency GPR data captured and processed in the provided data analysis 

software. The stepped-frequency system collects 21 parallel channels, which are displayed on 

both a depth plot (top photo of figure 32) and plan view scan slice (bottom photo of figure 32). 

The rectangular box indicates features classified as buried utility pipes according to VDOT 

documentation. 

 Source: FHWA.

Figure 32. Image. Images show an example of a stepped-frequency GPR scan collected

during field testing at Windsong Way. 

In contrast to the DF antenna GPR system, the stepped-frequency GPR system did not 

successfully map the full extent of the utilities, and many utilities were identified by only a 

single feature along their length. These low-quality results may have been caused by poor system

orientation during scans or utility lines running outside the roadways. 
44 

MASW Field Plan and Results

The field team used an MASW system consisting of a land streamer (i.e., inline array) with 24 

vertical-component geophones and a 24-channel seismic recorder. The individual geophones in

the array were coupled to the ground using spikes (“spiked” lines) or weights to allow for easier

data collection (“streamer” lines), with 1-ft geophone spacing for spiked lines and 3.3-ft for

streamer lines (figure 33). The MASW rental system also included a laptop computer to control 

the seismograph and data collection.

Source: FHWA. 

Figure 33. Photo. MASW data collection using a streamer geophone array at Settlers Ridge

setup 9, deployed on asphalt. 

MASW data collection uses a strategy known as “shoot-through roll-along” acquisition that

produces multiple seismic records (collections of time histories) with the same source-to-receiver

offsets and geophone array lengths. Each acquisition layout is designed for a specific

investigation depth to maximize the accuracy of the final subsurface images. For the field tests,

the MASW team tried three MASW data-acquisition strategies. One approach involved having 

six source locations on the ends of the array at various offsets (noted as “standard” approach in

table 5). The second method was a shoot-through approach that involved moving the source 

through the geophone array, also known as roll-along. The third method was a partial shoot‐

through approach that involved moving the source through the center of the array. Figure 34

depicts the most successful acquisition setup to detect buried utilities (setup 2). 
45 

Source: FHWA. 

Figure 34. Graph. MASW data-acquisition strategy used during field testing denotes a 

“shoot-through” approach where the geophone array remained in place and the source

positions varied.

To induce ground motion, the field crew employed 1.5-lb and 4-lb double-ended metal hammers

to strike metal plates on the ground. These lightweight sources were sufficient for the shallow 

targets of interest (under approximately 13 ft). The data records were stacked over three hammer

swings per source location to increase the data signal-to-noise ratio. Field personnel designed the 

layout at each setup to detect a primary target near the middle of the geophone array and a 

secondary target (if one existed) closer to an end of the array. The team conducted five or more 

layouts at each of the three testing locations (Spring Hill, Settlers Ridge, and Windsong Way) 

using the streamer and/or spiked geophone line on targets of various diameter, material, and

estimated depth (table 5).

The postacquisition analysis of MASW data follows a multistep processing procedure to

generate a 2D image of the subsurface shear-wave velocities (VS). In the first step, surface-wave

dispersion analysis is performed on the waveforms recorded at each geophone position to capture

the behavior of the surface waves as a function of frequency. Then, dispersion curves are

selected and inverted to produce one-dimensional (1D) VS profiles, and the 1D VS profiles are

interpolated to create a final 2D VS image (Park et al. 2007). Buried subsurface objects show up 

as low-VS anomalies in the final MASW results.

As a general rule of thumb, the MASW technology can resolve underground feature diameters

greater than approximately 30 percent of their emplacement depth. For example, MASW can

resolve a 1-ft diameter pipe if its depth is less than 3.3 ft. It is possible to achieve finer resolution 
46 

for shallow targets, but higher resolution is largely dependent on geophone spacing along the 

MASW array.1

 

To determine the range of conditions over which MASW detected buried utilities, the field team

acquired MASW data with different hammer-source weights and geophone spacing over pipes 

with various diameters and emplacement depths. The field tests conclusively showed that the 

shoot-through approach data-acquisition strategy was the only successful layout used to detect

buried utilities. Unfortunately, most of the MASW data were collected using setup 1 (“standard”) 

acquisition layout, and most of the utilities were too small or deep to be detected successfully. 

1

Dr. Choon Park, personal communication, 2021. 
47 

Table 5. MASW experimental setups and utility detection results.

—No data.

Setup

No. Location LineType Setup PrimaryTarget

Primary

Diameter

(inches)

Primary

Depth

(ft)

Primary

Target

Detected?

Secondary

Target

Secondary

Diameter

(inches)

Secondary

Depth (ft)

Secondary

Target

Detected?

1 Spring Hill Streamer Standard PVC water 8 3 N PVC sewer 8 7 N

2 Spring Hill Streamer Standard PVC sewer 8 7 N PVC water 8 3 N

3 Spring Hill Streamer Standard PVC water 8 3 N PVC sewer 8 9 N

4 Spring Hill Streamer Standard PVC sewer 8 3 N — — — —

5 Spring Hill Streamer Standard PVC water 8 3 N — — — — 

6 Settlers Ridge Spike Standard PVC water 4 4 N — — — — 

7 Settlers Ridge Spike

Shootthrough

approach

PVC water 4 4 Y — — — — 

8 Settlers Ridge Streamer Standard PVC water 4 4 N — — — — 

9 Settlers Ridge Streamer

Partial

shootthrough

approach

PVC sewer 8 10 N — — — — 

10 Settlers Ridge Streamer Standard PVC water 8 4 N PVC sewer 8 10 N

11 Settlers Ridge Streamer

Shootthrough

approach

PVC sewer 8 10 Y PVC water 8 4 Y 

12 Settlers Ridge Streamer Standard PVC sewer 8 10 N PVC water 8 1 N 

13 Windsong Way Spike Standard PVC sewer 4 1.5 N Copper

water 0.75 1 N 

14 Windsong Way Spike Standard PVC sewer 4 1.5 N Copper

water 0.75 9.5 N 

15 Windsong Way Streamer Standard PVC water 8 3 N PVC sewer 8 — N 

16 Windsong Way Streamer Standard PVC sewer 8 9.5 N — — — — 

17 Windsong Way Streamer Standard PVC water 8 3 N — — — — 

18 Windsong Way Streamer Standard PVC sewer 8 9.5 N — — — —
48 

MASW Example Results—Settlers Ridge Setup Number 11 (SR11) 

For SR11 in table 5, the field team used the partial shoot‐through data-acquisition approach. A 

commercial software package was used to process MASW data by using 12 geophone traces at a 

time and sweeping through the waveform dispersion analysis. An analyst manually selected a 1D 

dispersion curve for each geophone location, and the software inverted the curves to produce a 

2D shear-velocity map. MASW theory dictates that buried utilities should appear as low-velocity

zones in the 2D shear‐wave velocity images. The SR11 results in figure 35 show two

low-velocity zones that correlate well with the expected depths of the water and sewer pipes. 

Source: FHWA. 

Figure 35. Image. SR11 2D shear-velocity profile versus depth. Two anomalous low‐

velocity zones appear near the expected locations of buried utility lines (Jalinoos 2022). 

At this site, an 8-inch PVC sewer line is located at a depth of 10 ft, but the 2D MASW image

places it closer to 13 ft. The site maps indicate a 4-inch PVC water pipe at a depth of 4 ft. 

MASW located it closer to a 3-ft depth. These results indicate the usefulness of MASW to detect

and approximately locate utility lines, although the pipe diameter is not well constrained using 

standard processing techniques.

MASW Example Results—Settlers Ridge Setup Number 7 (SR7)

At the SR7 site, the field team used a full shoot-through approach with a 1-ft geophone spacing

to detect a shallow target. The same MASW processing procedure used for SR11 was applied to

the SR7 data. The analyst manually selected a full set of dispersion curves and performed

inversion to generate the final VS profile shown in figure 36. For the SR7 setup, a low-velocity

zone was identified near the location and depth expected of the 4-inch water pipe (figure 36).
49 

Source: FHWA. 

Figure 36. Image. SR7 2D shear wave velocity profile showing an anomalous low-velocity

zone near the depth of the target pipe (4-inch PVC water line).

Summary of MASW Results

The results provide evidence that MASW technology can detect and approximately locate utility

lines, particularly with the right acquisition strategies and streamer array parameters.

Specifically, using the shoot-through MASW acquisition strategies led to clear detections of 

utilities at Settlers Ridge setups 11 and 7, including 4-inch water lines at 3.3- and 4-ft depths and

an 8-inch sewer line at a depth of 10 ft. Geophone spacing and the appropriate source weights are

key parameters for a successful application of MASW to detect buried utilities.

Furthermore, while the MASW method can successfully image the locations and depths of 

buried utilities, it is unable to resolve pipe diameters with confidence. The MASW technology is

still not suitable as a standalone detection method of underground utilities, but it can be used as

an auxiliary method to increase confidence in the results from other NDE technologies or as an

alternative method when GPR or other methods are unsuccessful. 

APL Field Plan and Results

The field team expected the APL to perform poorly at the Virginia test sites, which consisted

primarily of paved or concrete surfaces. In these settings, acoustic waves experience high 

attenuation due to the stiff surface media, and soil inhomogeneities beneath the surface, such as

air voids, increase uncertainties in APL measurements. With these limitations in mind, the team

selected APL scan lines perpendicular to known buried utilities and prioritized acquisition

locations with soil rather than pavement. The crew collected APL measurements every 6 inches

along the length of each scan line, with the APL tool oriented perpendicular to buried utility

lines. Figure 37 shows an image of the APL instrument in use.

Potential 4-inch water pipe. 

Expected depth 4 ft. 
50 

Source: FHWA. 

Figure 37. Photo. APL system in use during field testing.

Analysis of the APL data involved a review of the acoustic responses gathered during testing to

identify the presence of anomalies that might indicate a buried utility. Pipe detection with the 

APL instrument requires multiple field conditions to be met—the most important is a difference

in subsurface sound speed between the pipe and the surrounding soil. While some APL scans

revealed impedance mismatches in the acoustic signatures, their locations did not generally align

with known subsurface target positions. Many of the field site utilities were buried beneath

roadways and sidewalks, where the APL tool is known to be less effective. Even the APL scans

performed over soil produced noisy signatures that made it impossible to identify features related

to buried utilities confidently. Figure 38 presents a typical example of the APL data collected

during the VDOT field tests. 

Source: FHWA. 

Figure 38. Image. Example of an APL scan collected during field testing.

FDEM Instrument Field Plan and Results

The project team used a frequency-domain ground conductivity meter to collect FDEM

measurements. The FDEM-based instrument is sensitive to changing soil conditions, and
51 

variations in surface conditions or subsurface geological layers can present challenges for system

accuracy. In general, the instrument operates in a similar fashion to GPR: it is most sensitive to

conductive buried objects and produces a signal feature that shows up as a contrast from the 

background. FDEM’s advantage is that the system presents no logistical challenges for data

collection because it is completely mobile and unaffected by terrain. Because the buried utility

lines at the three VDOT field sites were mostly made of PVC, the FDEM instrument’s

performance was substandard. 

The team collected FDEM data along the same scan lines used for the GPR data collection (i.e., 

scan lines perpendicular to the buried utility pipes) with the instrument oriented in the horizontal 

direction. A GPS unit connected to the data-collection system tracked the position of the 

instrument during each scan. Figure 39 presents an image of the FDEM conductivity meter in use 

during field tests.

Source: FHWA. 

Figure 39. Photo. FDEM system in use during field testing.

Analysis of the FDEM data involves a review of relative conductivity measurements made along 

linear scan paths. The presence of significant conductivity minima in the data indicate the 

presence of a conductive pipe. Figure 40 presents a typical example of FDEM data collected

along a Settlers Ridge scan line with known PVC subsurface targets. Variable surface conditions 

near the scan path’s start point (approximately 0–10 ft) likely caused the initial variability of the 

relative conductivity measurements. The measurements varied less as the FDEM instrument 

encountered a more uniform section of roadway. Buried utilities should show up as significant 

negative peaks relative to average, but this particular scan did not reveal any subsurface features

of note. The VDOT field sites generally contained nonconductive PVC utility lines, and

consequently, none of the FDEM scans successfully detected any buried utility lines. These
52 

results mirror the findings in the soil box laboratory work, where a similar FDEM system was

unsuccessful in detecting PVC pipes. 

Source: FHWA. 

Figure 40. Image. Typical example of an FDEM scan collected during field testing (Settlers

Ridge, scan line 6). 

FIELD TEST CONCLUSIONS

The field tests conducted at three VDOT sites mostly confirmed the soil box laboratory results

discussed previously, although the three sites presented significantly tougher conditions than

expected, particularly for the EM NDE technologies (GPR and FDEM).

The GPR field results varied significantly depending on the particular system used. In general,

the DF antenna system fared much better than the stepped-frequency system. This was mostly

due to the stepped-frequency system’s restricted use to paved roadways, but even when used on 

roadways, the stepped-frequency system was incapable of tracking utility lines below 

approximately 3.5 ft. In contrast, the DF antenna GPR found utilities at most testing sites. The

DF antenna feature of the GPR system increased subsurface resolution and penetration depths, 

which allowed nonconductive utility pipes to be found in several scans.

The MASW method successfully detected and located buried utilities, but only when the field

team implemented a survey design that increased the signal-to-noise ratios of the surface waves

propagating directly over the presumed utility locations. Although not presented in this report,

the MASW data also showed indications of higher-mode, surface-wave energy that could 

enhance the 2D subsurface VS images and provide greater certainty of utility location and depth. 

Additional research and fieldwork are suggested to confirm the success of MASW for locating

buried utilities and the variable setup parameters required to detect pipes of different diameters at

various depths. 
53 

CHAPTER 6. NDE TECHNOLOGY RECOMMENDATIONS

This study produced several recommended NDE technologies that are capable of detecting and

locating buried utilities. GPR remains the most reliable and consistent NDE method available for

the buried utility application, while the use of the FDEM was not applicable as the field test sites

did not offer any conductive utility pipes for detection. In addition, the study results mostly

demonstrate the current state of the art in GPR technology (multifrequency GPR and

stepped-frequency GPR), as GPR is already an established method for utility location. 

Although data were gathered in line with the standard procedures and settings for the system,

APL was inconclusive in the detection of any buried utilities in either laboratory or field-testing

conditions. It may be possible for the APL data-acquisition strategies to be improved to increase

their relevance for the buried utility application, or perhaps these data types could supplement 

the results from GPR or MASW. Various field conditions could have influenced the APL

readings as well, such as inhomogeneous soil conditions that interfered with the built-in

processing methods. 

Seismic methods such as MASW proved to be a new emerging technology for NDE based on 

success at locating the buried utilities at the Windsong Way field site in southern Virginia.

MASW should not yet be considered a standalone NDE technology for buried utility detection

and location, but it is the most promising non-GPR technology investigated so far. Further 

investigation of best-practice acquisition strategies and improved data processing could place

MASW well ahead of other NDE technologies, particularly for nonconductive pipe materials

emplaced at depths below approximately 4 ft.

By conducting fundamental, comprehensive research of existing and emerging NDE

technologies, this project successfully tested and identified various NDE technologies to detect

and locate various buried utilities. Table 6 lists the various technologies, their setup parameters,

ideal testing conditions, and the project team’s recommendations. 
54 

Table 6. Recommendations of NDE technologies. 

Method Technology 

Suggested Setup 

and Usage 

Parameters

Ideal 

Conditions Recommendations 

GPR

Multifrequency 

impulse GPR

Use wide 

spectral band 

wherever possible; 

prioritize low 

frequencies in the 

100–400 MHz range.

Homogeneous 

soil conditions 

with little to 

no clay.

Multifrequency and 

stepped-frequency GPR 

recommended for 

detection of buried 

utilities, particularly for 

metallic pipes. Stepped-frequency 

GPR

Use operator-driven 

GPR for rugged 

and nonideal 

field conditions.

Dry 

environments.

Use vehicle-mounted 

GPR under ideal 

conditions for highspeed data collection.

Relatively 

flat, firm, and 

even surface 

conditions 

for scanning.

EM 

technologies

Pipe and cable 

locators

Cycle through 

frequency-detection 

modes on the 

locator to identify 

most effective for a 

utility type.

Homogeneous 

soil conditions 

with little to 

no clay.

Recommended for 

detecting active cables or 

where connection can be 

made to the buried utility 

to support the locator.

Dry 

environments.

Passive location 

modes not recommended 

for detecting unpowered 

utilities.

FDEM

method

Cycle through 

frequency-detection 

modes on the 

locator to identify 

most effective for a 

utility type.

Homogeneous 

soil conditions 

with little to 

no clay.

Recommended for 

detection of shallow 

metallic pipes; lack of a 

real-time display reduces 

its effectiveness for 

utility location.

Dry 

environments.

Relatively 

flat, firm, and 

even surface 

conditions 

for scanning.
55 

Method Technology 

Suggested Setup 

and Usage 

Parameters

Ideal 

Conditions Recommendations 

Acoustic 

technologies APL

Select 6-inch 

instrument spacing 

to ensure an 

effective density 

of data points.

Homogeneous 

soil conditions 

with little to 

no clay.

Inconclusive for 

utility detection.

Select deep-mode 

data collection 

to ensure instrument 

captures effective 

depth. 

Dry 

environments.

Relatively 

flat, soft, and 

even surface 

conditions 

for scanning.

Seismic 

technologies

MASW

Minimum of 24 

geophones and a 

shoot-through 

approach 

recommended.

Pipe depths 

from 3 to 12 ft.

MASW recommended 

for further testing 

with shoot-through 

acquisition geometry. Source weight 

between 1.5 and 4 lb 

for pipes <15 ft.

Sensor 

locations on 

soil, grass, 

or asphalt.

Good 

impedance 

contrast 

between utility 

and soil.

HVSR

Requires at least four 

broadband sensors 

at a minimum 

spacing equal to 

pipe diameter.

General 

location of 

utilities must 

be known 

due to the 

time required 

to apply 

the technique 

(approximately 

30 min/site). 

Inconclusive for 

utility detection.

57 

ACKNOWLEDGMENTS 

Figure 4 is republished with permission of Elsevier Science & Technology Journals, from 

“Testing the Horizontal to Vertical Spectral Ratio Technique as a Tool for Utility Detection” by 

A. Khalil, G. Anukwu, and M. Nordin in the Journal of Applied Geophysics, volume 173, 2020. 

Permission conveyed via Copyright Clearance Center, Inc. 

The maps in figure 26, figure 27, and figure 28 in this document were modified. The original 

maps are the copyright property of Google® EarthTM and can be accessed from 

https://www.google.com/earth/ (Google® 2021). The map overlays showing the placement of 

utility locations, elevations, and type indicated with green (sewer) or cyan (water) dashed lines 

were developed as part of this research project. 

59 

REFERENCES

Al-Shayea, N. A., R. D. Woods, and P. Gilmore. 1994. “SASW and GPR to Detect Buried 

Objects.” Proceedings of the Symposium on the Application of Geophysics to 

Engineering and Environmental Problems. Wheat Ridge, CO: Environmental and 

Engineering Geophysical Society. 

Anspach, J. 1995. “Subsurface Utility Engineering: Upgrading the Quality of Utility 

Information.” Proceedings of the International Conference on Advances in Underground 

Pipeline Engineering. New York, NY: American Society of Civil Engineers (ASCE). 

ASCE. 2002. Standard Guidelines for the Collection and Depiction of Existing Subsurface 

Utility Data. New York, NY: American Society of Civil Engineers, Codes and Standards 

Activity Committee.

Badsar, S., M. Schevenels, W. Haegeman, and G. Degrande. 2010. “Determination of the 

Material Damping Ratio in the Soil from SASW Tests Using the Half-Power Bandwidth 

Method.” Geophysical Journal International 182: 1493–1508. 

Chemekoff, J., and D. Toussaint. 1994. “Pipe Location Technology Has Rich History.” Water 

Engineering and Management 141, no. 4: 28–31. 

Daniels, D. (Ed.). 2004. Ground Penetrating Radar (second ed., Vol. 1). London: The Institution 

of Electrical Engineers.

Datta, S., and S. Sarkar. 2016. “A Review on Different Pipeline Fault Detection Methods.” 

Journal of Loss Prevention in the Process Industries 41: 97–106. 

Dolphin, L. 1997. Ground Penetrating Radar (GPR) Usage and Limitations. Retrieved from 

Lambert Dolphin Library. http://www.ldolphin.org/GPRLimits.html, last accessed 

August 25, 2022. 

European Commission—Research General Directorate. 2004. “Guidelines for the 

Implementation of the H/V Spectral Ratio Technique on Ambient Vibrations 

Measurements, Processing, and Interpretation.” No. EVG1-CT-2000-00026 SESAME. 62. 

Brussels, Belgium: European Commission. 

Fernández, J., L. Hermanns, A. Fraile, E. Alarcón, and I. Del Rey. 2011. “Spectral Analysis 

Surface Waves Method in Ground Characterization.” Procedia Engineering 10: 3202–

3207. 

García-Jerez, A., J. Piña-Flores, F. J. Sánchez-Sesma, F. Luzón, and M. Perton. 2016. “A 

Computer Code for Forward Calculation and Inversion of the H/V Spectral Ratio Under 

the Diffuse Field Assumption.” Computers & Geosciences 97: 67–68. 

GEOVision. 2016. Spectral Analysis of Surface Waves Method. Retrieved July 2020, from 

GEOVision Geophysical Services: www.geovision.com. 
60 

Google®. 2021. Google® EarthTM. Retrieved from https://www. google.com/earth. 

Grandjean, G., J. C. Gourry, and A. Bitri. 2000. “Evaluation of GPR Techniques for CivilEngineering Applications: Study on a Test Site.” Journal of Applied Geophysics 45, 

no. 3: 141–156. 

Grivas, D. A. 2006. Applications of Ground Penetrating Radar for Highway Pavements. Institute 

for Infrastructure Asset Management. Latham, NY: New York State Department of 

Transportation. 

Hammon III, W. S., G. A. McMechan, and X. Zeng. 2000. “Forensic GPR: Finite-Difference 

Simulations of Responses from Buried Human Remains.” Journal of Applied Geophysics 

45, no. 3: 171–186. 

Hamran, S. E., T. Guneriussen, J. O. Hagen, and R. Odegard. 1997. “Ground Penetration Radar 

and ERS SAR Data for Glacier Monitoring.” International Geoscience and Remote 

Sensing Symposium Proceedings 2: 634–636. IGARSS'97. Piscataway, NJ: Institute of 

Electrical and Electronics Engineers (IEEE).

Hamran, S., and K. Langley. 2004. “A 5.3 GHz Step-Frequency GPR for Glacier Surface 

Characterisation.” Proceedings of the Tenth International Conference on Ground 

Penetrating Radar: 761–764. IEEE. Piscataway, NJ: IEEE.

Hawari, A., M. Khader, W. Hirzallah, T. Zayed, and O. Moselhi. 2017. “Integrated Sensing 

Technologies for Detection and Location of Leaks in Water Distribution Networks.” 

Water Science and Technology: Water Supply 17, no. 6: 1589–1601. 

Hubbard, S., J. Chen, K. Williams, Y. Rubin, and J. Peterson, J. 2005. “Environmental and 

Agricultural Applications of GPR.” Proceedings of the 3rd International Workshop on 

Advanced Ground Penetrating Radar: 45–49. IEEE. Piscataway, NJ: IEEE. 

Hutchinson, P. J., and M. H. Beird. 2016. “3D Mapping with MASW.” The Leading Edge 35,

no. 4: 350–352. 

Jalinoos, F. 2022. TechBrief: Availability, Feasibility, and Reliability of Available 

Nondestructive Evaluation Technologies for Detecting and Locating Buried Utilities. 

FHWA‐HRT‐22‐111. Washington, DC: Federal Highway Administration. 

Jaw, S. W., and M. Hashim. 2013. “Locational Accuracy of Underground Utility Mapping Using 

Ground Penetrating Radar.” Tunnelling and Underground Space Technology 35: 20–29. 

Jeng, Y., and C.-S. Chen. 2012. “Subsurface GPR Imaging of a Potential Collapse Area in Urban 

Environments.” Engineering Geology 147: 57–67. 

Jeong, H. S., and D. M. Abraham. 2004. “A Decision Tool for the Selection of Imaging 

Technologies to Detect Underground Infrastructure.” Tunnelling and Underground Space 

Technology 19, no. 2: 175–191. 
61 

Kavi, J. 2018. Detection of Buried Non-Metallic (Plastic and FRP Composite) Pipes Using GPR 

and IRT. Graduate Theses, Dissertations, and Problem Reports. 3724. West Virginia 

University. 

Khalil, A. E., G. C. Anukwu, and M. N. Nordin. 2020. “Testing the Horizontal to Vertical 

Spectral Ratio Technique as a Tool for Utility Detection.” Journal of Applied Geophysics 

173: 10398. 

Lai, W. W.-L., X. Dérobert, and P. Annan. 2018. A Review of Ground Penetrating Radar 

Application in Civil Engineering: A 30-Year Journey from Locating and Testing to 

Imaging and Diagnosis. NDT&E International 96: 58–78. 

Langman, A., and M. R. Inggs. 1998. “A 1-2 GHz SFCW Radar for Landmine Detection.” 

Proceedings of the 1998 South African Conference on Communications and Signal 

Processing-COMSIG'98: 453–454. IEEE. Piscataway, NJ: IEEE. 

Lin, C. P., C. H. Lin, and C. J. Chien. 2017. “Dispersion Analysis of Surface Wave Testing–

SASW vs. MASW.” Journal of Applied Geophysics 143: 223–230. 

Liu, Y., D. Habibi, D. Chai, X. Wang, H. Chen, Y. Gao, and S. Li. 2020. “A Comprehensive 

Review of Acoustic Methods for Locating Underground Pipelines.” Applied Sciences 10, 

no. 3: 1031. 

Manacorda, G., H. Scott, P. D. Loach, J. J. Kazik, D. Pinchbeck, M. Remeil, J. Capdevielle, and 

P. Fournier. 2004. “The European GIGA project.” Proceedings of the Tenth International 

Conference on Ground Penetrating Radar (GPR) 1: 355–358. IEEE. Piscataway, NJ: 

IEEE. 

Mendecki, M. J., B. Bieta, and M. Mycka. 2014. “Determination of the Resonance FrequencyThickness Relation Based on the Ambient Seismic Noise Records from Upper Silesia 

Coal Basin.” Contemporary Trends in Geoscience 3, no. 1: 41–51. 

Metje, N., P. R. Atkins, M. J. Brennan, D. N. Chapman, H. M. Lim, J. Machell, and A. M. 

Thomas. 2007. “Mapping the Underworld–State-of-the-Art Review.” Tunnelling and 

Underground Space Technology 22: no. 5–6, 568–586. 

Metwaly, M. 2015. “Application of GPR Technique for Subsurface Utility Mapping: A Case 

Study from Urban Area of Holy Mecca, Saudi Arabia.” Measurement 60: 139–145. 

Miller, R. D., C. B. Park, J. M. Ivanov, J. Xia, D. R. Laflen, C. Gratton, and R. Overton. 2000. 

MASW to Investigate Anomalous Near-Surface Materials at the Indian Refinery in 

Lawrenceville, Illinois. Open-File Report No. 2000-4. Lawrence, KS: Kansas Geological 

Survey. https://www.kgs.ku.edu/, last accessed September 9, 2022. 

Moorman, B. J., and F. A. Michel. 2000. “Glacial Hydrological System Characterization Using 

Ground‐Penetrating Radar.” Hydrological Processes 14, no. 15: 2645–2667. 
62 

Nakamura, Y. 1989. “A Method for Dynamic Characteristics Estimation of Subsurface Using 

Microtremor on the Ground Surface.” Railway Technical Research Institute, Quarterly 

Reports 3, no. 1. 

Neal, A. 2004. “Ground-Penetrating Radar and Its Use in Sedimentology: Principles, Problems 

and Progress.” Earth-Science Reviews 66, no. 3–4: 261–330. 

Papandreou, B., E. Rustighi, and M. J. Brennan. 2008. A Study into the Feasibility of Using 

Acoustic Techniques to Locate Buried Objects. ISVR Technical Memorandum No. 979. 

University of Southampton Institute of Sound and Vibration Research. 

Park, C. B., R. D. Miller, and J. Xia. 1996. “Multi-Channel Analysis of Surface Waves Using 

Vibroseis (MASWV).” SEG Technical Program Expanded Abstracts 1996. 68–71. 

Society of Exploration Geophysicists. 

Park, C. B., R. D. Miller, and J. Xia. 1999. “Multichannel Analysis of Surface Waves.” 

Geophysics 64, no. 3: 800–808. 

Park, C. B., R. D. Miller, J. Xia, and J. Ivanov. 2007. “Multichannel Analysis of Surface Waves 

(MASW)—Active and Passive Methods.” The Leading Edge 26, no. 1: 60–64. 

Park, C. B., R. D. Miller, M. Brohammer, J. Xia, and J. Ivanov. 2000. Using SurfSeis© 2000 for 

Multichannel Analysis of Surface Waves (MASW): User’s Manual. Lawrence, KS: 

Kansas Geological Survey, October. 

https://www.kgs.ku.edu/software/surfseis/SurfSeisMan.pdf, last accessed December 21, 

2022. 

Park, Y. J., K. H. Kim, S. B. Cho, D. W. Yoo, D. G. Youn, and Y. K. Jeong. 2003. 

“Development of a UWB GPR System for Detecting Small Objects Buried Under 

Ground.” Proceedings of IEEE Conference on Ultra Wideband Systems and 

Technologies: 384–388. IEEE. Piscataway, NJ: IEEE. 

Park, Y. J., K. H. Kim, S. B. Cho, D. W. Yoo, D. G. Youn, and Y. K. Jeong. 2004. October. 

“Buried Small Objects Detected by UWB GPR.” IEEE Aerospace and Electronic 

Systems Magazine 19, no. 10: 3–6. 

Plewes, L. A., and B. Hubbard. 2001. “A Review of the Use of Radio-Echo Sounding in 

Glaciology.” Progress in Physical Geography 25, no. 2: 203–236. 

Sauret, E. S. G., J. Beaujean, F. Nguyen, S. Wildemeersch, and S. Brouyere. 2015. 

“Characterization of Superficial Deposits Using Electrical Resistivity Tomography (ERT) 

and Horizontal-to-Vertical Spectral Ratio (HVSR) Geophysical Methods: A Case Study.” 

Journal of Applied Geophysics 121: 140–148. 

Scheers, B., M. Piette, and A. Vander Vorst. 1998. “The Detection of AP Mines Using UWB 

GPR.” Second International Conference on Detection of Abandoned Land Mines. 50–54. 

London, UK: The Institution of Engineering and Technology (IET). 
63 

Sciotti, M., F. Colone, D. Pastina, and T. Bucciarelli. 2003. “GPR for Archaeological 

Investigations: Real Performance Assessment for Different Surface and Subsurface 

Conditions.” IGARSS IEEE. 2003 International Geoscience and Remote Sensing 

Symposium Proceedings 4. IEEE. Piscataway, NJ: IEEE.

Sterling, R. L., J. Anspach, E. Allouche, J. Simicevic, C. D. Rogers, K. E. Weston, and K. 

Hayes. 2009. Encouraging Innovation in Locating and Characterizing Underground 

Utilities. Report S2-R01-RW. Washington, DC: The National Academies Press. SHRP 2 

Transportation Research Board. 

Talwani, M., and W. Kessinger. 2003. Exploration Geophysics. In Encyclopedia of Physical 

Science and Technology. Third ed. 709–726. San Diego: CA: Academic Press. 

Telford, W. M., L. P. Geldart, and R. E. Sheriff. 1990. Applied Geophysics. Second ed. 

Cambridge, UK: Cambridge University Press. 

Thompson, E. M., L. G. Baise, Y. Tanaka, and R. E. Kayen. 2012. “A Taxonomy of Site 

Response Complexity.” Soil Dynamics and Earthquake Engineering 41, no. 32–43. 

Vickridge, I. G., and D. Leontidis. 1997. Sewer Surveys. In Sewers—Rehabilitation and 

Construction Repair Vol. 1 Repair and Renovation. 84–102. London: Arnold. 

Wightman, W. E., F. Jalinoos, P. Sirles, and K. Hanna. 2003. Application of Geophysical 

Methods to Highway Related Problems. FHWA-IF-04-021. Lakewood, CO: Federal 

Highway Administration Central Federal Lands Highway Division. 

Xia, J., R. D. Miller, and C. B. Park. 1999. “Estimation of Near-Surface Shear-Wave Velocity by 

Inversion of Rayleigh Waves.” GEOPHYSICS 64, no. 3: 691–700. 

Xia, J., R. D. Miller, C. B. Park, J. Hunter, D. Laflen, R. Good, and C. Gratton. 1998. 

Comparison of Shear Wave Velocities from MASW Technique and Borehole 

Measurements in Unconsolidated Sediments of the Fraser River Delta. Open-file Report 

98-58. Lawrence, KS: Kansas Geological Survey. 

Xiaojian, Y., Y. Haizhong, and W. Huiliang. 1997. “The Applications of GPR to Civil 

Engineering in China.” IGARSS'97. 1997 IEEE International Geoscience and Remote 

Sensing Symposium Proceedings. Remote Sensing—A Scientific Vision for Sustainable 

Development 1: 232–234. IEEE. Piscataway, NJ: IEEE. 

Yarovoy, A., A. Schukin, I. Kaploun, and L. Ligthart. 2003. “Multi-Waveform Full-Polarimetric 

Video Impulse Radar for Landmine Detection.” 2003 33rd European Microwave 

Conference 1003–1006. IEEE. Piscataway, NJ: IEEE. 

Young, G. N., and C. M. Kennedy. 2015. Utility Locating Technology Development Using 

Multisensor Platforms. No. SHRP 2 Report S2-R01B-RW-1. Washington, DC: The 

Transportation Research Board of the National Academies of Sciences, Engineering, and 

Medicine.


HRDI-30/07-23(WEB)E Recycled

Recyclable

Recommended citation: Federal Highway Administration,

Availability, Feasibility, and Reliability of Available Nondestructive Evaluation (NDE) 

Technologies for Detecting and Locating Buried Utilities: Final Report 

(Washington, DC: 2023) https://doi.org/10.21949/1521981