he U.S. Geological Survey 

 Cone Penetration Testing 

(CPT) truck is a fast and inexpensive way to conduct shallow 

subsurface exploration. Detailed 

data are available immediately, 

permitting on-the-fl y mapping of 

stratigraphy and other subsurface 

features. CPT is a useful tool in 

geologic-hazard, hydrologic and 

environmental studies. This rapid 

and cost-effective approach is 

particularly advantageous in 

urban environments because no 

drill spoils are produced. The CPT 

truck is available on a reimbursable basis to all USGS staff and 

cooperators. 

T 

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 028–03

2003

Subsurface Exploration with the Cone 

Penetration Testing Truck

Friction

ratio

Relative

tip resistance

Soil type Shear-wave velocity

(in meters per second)

0

N

6

–12

Artificial

fill

0

–1

–2

–3

–4

118

Mud

4

–5

N–6

METERS

103

Silty sand

6

DEPTH,IN –7

–8

–9

–10

225

Dense sand

12

–11

419

Cone penetration testing (CPT) permits 

rapid exploration of shallow (less than 30 

meters) subsurface conditions while minimizing 

retrieval of subsurface materials, an inconvenient and occasionally expensive byproduct of 

conventional drilling. This exploration method 

employs sensors that are pushed into the ground 

to infer the properties of both soils and pore 

fl uids. Known as direct-push technology, this 

method can map out the vertical and lateral 

extent of stratigraphic layers, as well as the distribution of subsurface contaminants. By using 

standard engineering correlations, the geotechnical properties of stratigraphic layers can also be 

inferred. 

In 1997, the Pacifi c Gas and Electric Co. 

(PG&E), under the PG&E–U.S. Geological 

Survey (USGS) Cooperative Research and 

Development Agreement (CRADA), contributed 

funds for the CPT truck. The PG&E–USGS 

CRADA was created to conduct earthquakehazard investigations and improve earthquake 

notifi cations needed for reducing earthquake 

risks in the San Francisco Bay Region. Since 

1998, the USGS CPT truck has provided data 

for a broad variety of USGS earthquake-hazard, 

geologic, and hydrologic investigations that 

require detailed subsurface information. 

A CPT sounding is made by pushing a 

small probe into the ground. Typically, a 3.6-

centimeter-diameter probe (cone) is pushed 

into the ground to depths ranging from 15 to 30 CPT log of friction ratio and relative tip resistance with inferred geologic units and their shear-wave velocities.
Printed on recycled paper

30 minutes. All holes, regardless of the type 

of tooling used, can be sealed by grouting if 

environmental regulations require backfi lling of 

holes. The USGS uses a pneumatic shear-wave 

generator capable of producing clean, repeatable shear waves essential for detailed seismicvelocity studies. 

 Cone Penetration Testing

 Advantages 

 • Rapid data acquisition

 • No drilling mess

 • Immediate data availability

 • Detailed subsurface information

 Capabilities

 • Shear-wave-velocity measurement

 • Detailed stratigraphic profiling 

 • Soil sampling

 • Pore-fluid-pressure/water-table measurement

 • Evaluation of liquefaction potential

 • Vane-shear measurement 

 • Video imagery

 • Vertical temperature profiling

 • Direct-push sensor installation

 • Ground-water sampling 

 • Monitoring wells 

 • Conductivity/resistivity measurements

 • Ground-penetrating radar 

 • Discrete-gas sampling

 • Regional and site-specifi c stratigraphy

 • Laser-induced fl uorescence

 • Volatile-organic-compound sensing

 Applications

 • Seismic-hazard mapping

 • Paleoseismic exploration

 • Ground-water-quality studies

 • Environmental-contamination studies

 • Regional or site-specific three-dimensional

 mapping of shallow sedimentary deposits

CPT applications are numerous and wide 

ranging. CPT measures the thicknesses and 

quantifi es the physical properties, including 

shear-wave velocity, of individual geologic 

units. In combination with maps of surfi cial 

geology, this method permits mapping of 

regional liquefaction hazards and National 

Earthquake Hazards Reduction Program 

(NEHRP) site-amplifi cation soil classes used 

for seismic design. CPT is well suited for 

mapping the elevations of buried stratigraphic 

horizons, as well as for reconnaissance of 

paleoseismic sites, the locations where sedimentary deposits may record evidence of prehistoric earthquakes. For example, CPT can be 

used to identify areas suitable for trenching of 

active faults, as well as excluding less desirable trench sites. Closely spaced CPT soundings aligned along a profi le provide detailed 

cross-sectional information, including lateral 

variation in composition and elevation changes 

of units. Recent advances in sensor technology 

have led to the use of CPT to install electricalresistivity-tomography (ERT) electrodes and 

provide access for ground-penetrating-radartomography (GPRT) antennas. ERT monitors 

and detects such subsurface processes as contaminant-plume migration. GPRT uses highfrequency radio waves transmitted from one 

subsurface location and received at a second 

location. The radar traveltimes image soil-horizon boundaries, buried objects, or faults. CPT 

is useful to ground-water studies by measuring 

pore pressure, measuring in-place permeability, 

and sampling ground water and soil gas. For 

environmental site investigations, volatileorganic-compound (VOC) sensors in the cone 

can identify the composition of contaminant 

plumes and map their distribution and extent. 

Subsurface video imagery obtained with a 

cone-mounted camera can measure grain size, 

using a 20× magnifying lens and fi ber-optic 

light source.

The U.S. Geological Survey CPT truck 

is available on a reimbursable basis for all 

research investigations by USGS staff and 

cooperators.The CPT truck provides a fast and 

inexpensive way to conduct shallow subsurface 

exploration. Detailed data are available immediately, permitting rapid mapping of subsurface 

features. CPT can expedite geologic-hazard, 

hydrologic, and environmental studies. This 

rapid and cost-effective approach is well suited 

for urban environments because no drill spoils 

are produced. 

Thomas E. Noce and Thomas L. Holzer

Edited by

George A. Havach

Graphic design by

Stephen L. Scott

For more information contact: 

Thomas E. Noce 

U.S. Geological Survey 

345 Middlefi eld Rd. MS 977

Menlo Park, CA, 94025 

Tel: (650) 329–4861 

Fax: (650) 329–5163 

email: tnoce@usgs.gov

This Fact Sheet and any updates to it are available 

online at:

 http://pubs.usgs.gov/fs/2003/fs028-03/

meters. The cone is advanced downward at a 

constant velocity of 2 centimeters per second, 

using hydraulic rams that apply the full 23-ton 

weight of the CPT truck to push the probe rods 

to depth. In typical CPT soundings, the resistance to penetration is measured. Continuous 

measurements are made of the resistance to 

penetration of the tip and the frictional sliding resistance of the sleeve of the cone. The 

penetration resistance, which is digitized at 

5-centimeter depth intervals, permits detailed 

inferences about stratigraphy and lithology. Soil 

type is inferred from a chart that compares these 

two measurements with the known physical 

properties of various soils.

CPT is a much more rapid and cost effective approach than conventional drilling for 

shallow subsurface exploration. Typically, four 

to fi ve 15- to 30-meter-deep soundings per day 

can be accomplished, in contrast to one or two 

per day with conventional drilling and sampling. Soundings also have the great advantage 

of not producing any drill cuttings, spoils, or 

fl uids. This aspect is particularly advantageous 

where subsurface contaminants are present or 

suspected. Data are automatically logged onto a 

rugged fi eld computer and are ready for immediate viewing and analysis in the fi eld. CPT is 

a reliable and effi cient method for stratigraphic 

profi ling and obtaining soil-engineering parameters for geotechnical design, as well as being 

widely accepted and encouraged by regulators 

as an effective environmental-investigation 

technology. 

Various sensors and tools

Many sensors and tools have been adapted 

to CPT technology, including electrical-resistivity modules, temperature and volatile-organiccompound (VOC) sensors, ground-water, soil, 

and discrete-gas samplers, seismometers, inplace vane shear, and video imaging. Though 

not designed for continuous coring, the CPT 

truck can collect discrete soil samples with a 

piston sampler. Either 20- or 60-centimeter-long 

samples can be retrieved from predetermined 

depths. Typically, a single sample can be 

obtained from a depth of 15 meters in less than 

EXPLANATION

Percentage of area

predicted to

liquefy

Not studied

Water

0

Less than 1

3

38

73

CPT location HAYWARD FAULT

0 2.5 5 10 KILOMETERS

N

Liquefaction-scenario seismic-hazard map of the greater Oakland, California, area for a magnitude 7.1 earthquake on 

the Hayward Fault. Geologic units were geotechnically characterized with 210 cone-penetration-test (CPT) soundings.