NBSIR 80-2106

Soil Impact Attenuation

Performance: A Field Study

William B. Seine

John R. Sorrells

Product Safety Technology Division

Center for Consumer Product Technology

National Engineering Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, D.C. 20234

June 1 980

Final

Prepared for Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, MD 20016

NBSIR 80-2106

SOIL IMPACT ATTENUATION

PERFORMANCE: A FIELD STUDY

William B. Beine

John R. Sorrells

Product Safety Technology Division

Center for Consumer Product Technology

National Engineering Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, D.C. 20234

June 1980

Final

Prepared for Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, MD 20016

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity, Technology, and Innovation

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director
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CONTENTS

Page

I. Introduction 1

Background 1

Purpose and Scope 1

II. Test Method and Equipment 1

Playground and Test Site Selection 3

III. Test Procedures 3

Soil Impact Performance Tests 3

Densicy-Moisture Content 4

Soil Classification Test Procedures 5

Asphalt Impact Performance Tests 5

IV. Test Results and Discussion 5

Soil Analyses 5

Impact Performance Data 9

Comparison of Field and Laboratory Results 11

V. Summary 11

Appendix A. Soil Analysis Reports 22

Appendix E. Soil Classification Chart 30

11
LIST OF TABLES

Table

No. Page

1 Classification of Soils 6

2 Measures of Soil Plasticity 7

3 Density and Moisture Contents of the Four

Soils at the Time of the Impact Perfo 2rmance

Tests 8

4 Impact Attenuation Perform.ance of Asphalt . . 11

LIST OF FIGURES

Figure

No. Page

l.a Monorail Support System 13

1.

b Typical Test Set-Up 13

2. a Headform and Carriage Assem.bly 14

2.b Signal Processing Equipment 14

3 Particle Size of the Four Playground Soils . 15

4 Soil Impact Attenuation Perform.ance - Playground 1 16

5 Soil Impact Attenuation Performance - Playground 2 17

6 Soil Im.pact Attenuation Perform.ance - Playground 3 18

7 Soil Impact Attenuation Performance - Playground 4 19

8 Soil Impact Attenuation Performance - All Playgrounds 20

9 Impact Performance of Soils and Other

Materials 21

111
Soil Impact Attenuation Performance: A Field Study

William B. Beine

John R. Sorrells

I. INTRODUCTION

Background

Recently the Center for Consumer Product Technology of the

National Bureau of Standards (NBS) completed a laboratory investigation of the impact attenuation performance of playground

surfacing materials.* Specifically, the objectives of that

research were (1) to develop a methodology for assessing the

impact attenuation performance of surfaces in relation to head

injury, and (2) to test surfacing materials commonly installed

under playground equipment to determine which surfacing materials,

if any, are capable of providing reasonable protection against

head injury. Eleven surfacing materials were tested in that

study. However, soil, because of its indefinite composition, was

not included in the test.

More recently. the Consumer Product Safety Commission (CPSC)

requested that the NBS conduct a very limited field study of the

impact attenuation capability of soil. This work began in late

August of 1979 and is the subject of this report.

Purpose and Scope

The objective of this research is to provide the CPSC with

an appraisal of the impact attenuation performance of different

soils and asphalt. The scope of this investigation was limited

to testing four soils and one asphalt surface at playground sites

in the Washington, D.C., metropolitan area.

II. TEST METHOD AND EQUIPMENT

There is a history of test method development for investigating

the ability of various products to attenuate an impact, especially

in protective headgear research. All of the recent test m.ethods

require dropping an instrumented headform in guided free fall and

measuring the linear acceleration of the headform during impact.

This was the method used in the earlier laboratory testing of

playground surfacing materials and in this study of soil and

asphalt.

*This effort was funded by the Consumer Product Safety Commission.

Documentation of that study can be found in the report, "Impact

Attenuation Performance of Surfaces Installed Under Playground

Equipment," NBSIR 79-1707.
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The equipment required by this test method consists of a

headform to impact the test material, an accelerometer mounted

at the center of gravity of the headform, a monorail to guide

the headform as it falls, instrumentation to record and display

the results of each test, and a velocity meter. Also, because

these tests were conducted on playgrounds, a vehicle to transport

the equipment, a mount to attach the monorail to the vehicle

and hold the monorail stationary during tests, and an AC power

source were required. The field test equipment is shown in

figures 1 and 2.

To facilitate mobility, the length of the existing monorail

was shortened to 9 feet. This permitted tests to be made from

drop heights up to 8 feet. The monorail was attached to the

vehicle by a mount which was fabricated specifically for this

purpose. This mount supports the monorail during testing and

incorporates provisions for aligning the monorail vertically.

To stabilize the monorail-mount-vehicle system, two hydraulic

jacks were employed beneath the frame of the vehicle on opposite

sides of the monorail. The ANSI size "C" headform was used to

impact the test surface. 1/ The headform was equipped with a piezoelectric linear accelerometer to measure the acceleration

imparted to the headform. The output of the accelerometer was

channeled through a signal conditioner to a storage oscilloscope

and a Severity Index (SI) analyzer. The peak acceleration

produced by each impact was displayed on the SI analyzer and

confirmed by the acceleration/time trace on the oscilloscope.

Power to operate the instrumentation was obtained from a

gasoline powered AC generator.

With the monorail test apparatus, the falling headform is

not actually in free fall because of friction between the

bearings of the headform carrier and monorail. Consequently,

the equivalent free fall distance of the headform is less than

the height of the headform at the time of its release. Determining the equivalent free fall distance of the headform is

accomplished by measuring the velocity attained by the

headform just prior to impact (using an optical velocity meter)

and computing the equivalent free fall distance from the relation

where

h = equivalent free fall distance,

V = velocity of the headform just prior to impact, and

g = gravitational constant (32.2 ft/sec^).

In the sections that follow, it is the equivalent or computed

drop height which is used.

2
Playground and Test Site Selection

The selection of playgrounds was guided by three criteria.

The playgrounds would:

1. be within the Washington, D.C., metropolitan area,

2. have different soil characteristics, and

3. be accessible to the test equipment.

While there are hundreds of playgrounds in the metropolitan

area, the limited resources of this project precluded an exhaustive

search for soils having a broad range of characteristics.

Furthermore, the urgency to initiate testing precluded coordinating and scheduling activities with several local park

authorities. Because of these constraints and the fact that

there is a sizeable acreage of park land in Montgom.ery County,

the Montgomery County Parks Director's office of the MarylandNational Capitol Park and Planning Commission (M-NCPPC) was

contacted. Subsequently, the M-NCPPC gave approval to conduct

tests on county park land and provided assistance in selecting

candidate test sites.*

Fourteen playgrounds were screened as likely candidates

for this study. These sites were visited by the NBS project

staff and representatives from AMBRIC Testing and Engineering

Associates of Virginia, Inc. (AMBRIC),** the Consumer Product

Safety Commission, and the M-NCPPC. This tour resulted in the

final selection of five playgrounds —four playgrounds for

impact performance testing of soil and one for testing asphalt.

Hereafter, these test sites are referred to as playgrounds 1,

2, 3, 4, and the asphalt surface.

III. TEST PROCEDURES

Soil Impact Performance Tests

Two series of soil impact performance tests were conducted

on each of the four playgrounds. This was specified in the

study design to enable testing the same soils at different

levels of moisture content. The first series was conducted on

September 17th and 18th, following a relatively dry period of

weather, and the second series was completed on October 4th,

1979, following a rainy period. Consequently, eight sets of

tests were conducted (four playgrounds at two different times)

*For this assistance the authors express their thanks to

W. Colpitts, Deputy Director of Parks, and members of his staff.

**Because of the wide variation in soil characteristics and the

expertise and equipment required to analyze and classify soils,

AMBRIC Testing and Engineering Associates of Virginia, Inc.

were contracted to ensure that the selection of sites satisfied

the second criterion and to perform subsequent soil analyses.

3
The same test procedures were used for each of the eight sets

of tests. Each set of tests consisted of six drops: tv/o drops

at a low height (approximately 3 feet) ; two drops at an intermediate height (approximately 5.5 feet) , and two drops at a high height (approximately 8 feet)

The surface area impacted in each test was selected from

within a narrow circular band between 6 and 12 inches beyond

the perimeter of the merry-go-round located on each playground.

This region was well suited for these tests because it offered

a surface which receives uniform and relatively heavy use, it

was easily accessible, and was large enough to provide 12 well

spaced and distinct impact sites (6 sites for each series).

Generally, on almost all playgrounds in the Montgomery

County Park system, the surface beneath and around play equipment

is covered with a layer of finely crushed rock or organic

material. With use, this material gradually is dispersed. The

thickness of the material remaining in the four impact regions

was usually between 0.5 and 1.5 inches. At each impact site,

this layer of loose material was removed to expose the underlying surface prior to each drop. The exposed surface of the

soil was then carefully leveled and examined for extraneous

material (e.g., stones or tree roots) embedded in the surface.

If such contamination was present, a different impact site was

prepared. The vehicle/monorail test apparatus was then positioned

so that the headform would impact the prepared surface. The

hydraulic jacks were placed beneath the frame of the vehicle

and adjusted, the monorail was plumbed, the velocity gauge was

adjusted, and the release height of the headform was set.

Finally, the headform was dropped onto the surface and the peak

acceleration and velocity at impact were recorded. For the

first series of tests, the specific location of each impact

site was also recorded. This enabled these sites to be excluded

from the second test series, thus avoiding impacting a previously

tested site.

Density-Moisture Content

At the time the impact tests were performed, the in-place

soil density and moisture content were measured with a nuclear

test meter. Two measurements* of density and moisture content

were obtained at each playground for each series of tests.

These measurements were performed by AMBRIC Engineering in

accordance with accepted ASTM practice.

*Only one measurement was obtained for playgrounds 3 and 4

during the first series.

4
Soil Classification Test Procedures

A sample of soil from each of the four playgrounds was

collected from the impact region and subsequently analyzed by

AMBRIC Engineering at their laboratory facilities. The purpose

of that analysis was to identify the soil type at each playground.

Each sample was subjected to (1) a particle size analysis to

determine the distribution of the particle size of each soil, (2)

tests to determine the relationship between moisture content and

density (standard Proctor test) of each soil, and (3) tests to

determine the liquid and plastic limits of the soils. All of

these tests were performed in accordance with accepted ASTM

practices

Asphalt Impact Performance Tests

The test procedures to determine the impact performance of

asphalt were basically the same as those used for soils. Notable

differences in the procedures were that asphalt was tested in

only the first series and, because of the high peak accelerations

obtained, the headform release height was limited to six inches.

Tests were performed at three sites on the asphalt surface, which

was part of a basketball court. This asphalt was estimated by

park officials to be approximately 6 inches thick and composed of

an ordinary "hot mix" material whose largest stone size was less

than 3/8 inch in diameter.

IV. TEST RESULTS AND DISCUSSION

Before reviewing the data , it must be remembered that the

scope of this study was extremely lim.ited. The indefinite and

complex character of soils, the inability to control important

study variables, such as moisture, density, and composition, in

conjunction with the limited number of test locations, confounds

the picture that the data might imply. Consequently, while we

have attempted to point out and explain differences and to

generalize our observations, much of the following discussion is

more descriptive than inferential.

Soil Analyses

Tables 1 and 2 and figure 3 show the results of the soil

analysis performed by AMBRIC. The complete reports prepared by

AMBRIC are included in Appendix A.

Soil deposits consist of solid soil particles, void spaces,

and water that may exist in the void spaces surrounding the

particles. The solid particles are basically disintegrated rock

of varying size and shape. In this study soils were classified

5
by the Unified Soil Classification System (ASTM D2487-69) in

which soil classification is primarily related to particle-size

distribution and plasticity.*

In the Unified Soil Classification System, there are four

major divisions of soil types--gravel , sand, silt, and clay.

These divisions are further subdivided into 14 categories. (See

Appendix B.) Descriptions of the soil types tested in this study

are shown in table 1.

The predominant soil type at the test sites was either a silt or a sand; however, the soils generally contained quantities

of other soil types as indicated by their description. For

example, a clayey, sandy silt indicates a mixture of clay and

sand with the predominant soil type, silt.

Table 1. Classification of Soils

Soil Classification

Playground Designation Description

1 ML Silt

2 ML-CL Gravelly Clayey Silt

3 SM-SC Clayey Sandy Silt

4 SM Micaceous Silty Clayey

Sand

As shown by figure 3, the soils all contained a large percentage

by weight of small or fine grained particles. At least 80 percent

of the total weight of each soil sample consisted of particles

less than .066 inch in diameter.

The differences in the particle-size distribution between the

four test sites are difficult to characterize. For example,

playground 4 had the lowest percentage of weight of particles

less than .003 inch in diameter, but also less than 3 percent of

its total weight was due to particles greater than .066 inch in

diameter. Consequently, the difficulty in characterizing the

*Plasticity is a measure of the soil ' s ability to be remolded

without raveling or breaking apart.

6
differences between the test sites, and the relatively large

percentage of fine grained particles less than .003 inch in

diameter, confounds any attempt to draw correlations between

particle-size distribution and the im.pact attenuation performance

of different soils.

The plasticity index of each soil sample was also determined

for the purpose of classifying the soil. The plasticity of a soil is characterized by two measures —the plastic limit and

the liquid limit. At a low water content a soil possesses the

properties of a solid. As the moisture content of the soil

increases, the soil acquires the properties of a semi-solid,

then a plastic, and finally, a liquid. The plastic limit is

the moisture content dividing the plastic and semi-solid state,

and the liquid limit is the division between the plastic and

liquid states. These limits are shown in table 2.

Table 2. Measures of Soil Plasticity

Playground

Plastic

Limit

Liquid

Limit

Plasticity

Index

1 27 32 5

2 15 21 6

3 16 19 3

4 — — Non-plastic

The plasticity index is the numeric difference between the

liquid and plastic limit. For three of the four soils tested,

the plasticity index was very similar and very low, less than 6

(see also Appendix B) . The soil of playground 4 was completely

non-plastic

In-place density and moisture content measurements were made

at the time each of the eight sets of tests were performed.

These measurements are shown in table 3.

7
Table 3. Density and Moisture Contents of the Four

Soils at the Time of the Impact Performance Tests

Playground

1

Dens

(pcf

Series

ity

Avg

1

Mo is

(%)

ture

Avg

Den

(pcf)

Seri

sity

es 2

Mo is

(%)

ture

107.9

103.9 (105.9) 14.814.2 (14.5) 102 .102.7 (102 .6)

14.3

14 .

(14.6)

2

103.8

101.7 (102.8) 12.0

11.1 (11.6) 101.9

102.6 ^ ^2 .3)

14 .

14.7 (14.4)

3 109.4 (109.4) 13 .

(13.7) 106.9

107.1 (107.0) 15.314.6 (15.0)

4 104.9 (104.9) 16 .

(16.0) 103.1

106 .

(104.6) 16.3

14 .

(15.5)

Mean (13.6) Mean (14.8)

Std. Dev. ( 1.7) Std. Dev. ( 0.7)

The in-place density (that is, the weight in pounds per

cubic foot of the soil in its undisturbed condition) of playground

3 was the greatest, and perhaps playground 2 was the least dense.

The greatest difference between any two density measurements,

however, was less than 8 pounds per cubic foot.

The amounts of precipitation observed at the NBS prior to

each test series was the major criterion for choosing the particular

test dates. Indeed, the difference in accumulated precipitation

just prior to each series was substantial, as indicated by the

local climatological data collected by the National Weather

Service. According to the Weather Service, no precipitation was

recorded* during the ten days preceding the first test series.

However, in the six days preceding the second test series, a total

of 2.6 inches of precipitation fell in the area. Even though such

a difference in precipitation v/as evident, only playground 2 and,

to a lesser extent, playground 3 exhibited higher moisture contents

for the second test series. In fact, the average of the two

moisture content measurements obtained for playground 4 for the

second test series was less than the moisture content measured in

the first series and, yet, pools of water remained on the playground's

surface at the time of the second test series.

*These data are collected by the National Weather Service at

Washington National Airport.

8
The increased precipitation prior to the second test series

did raise the average moisture content for the four playgrounds

(primarily due to the increases at playground 2 and playground 3)

and also reduced moisture content differences between the four

soils

There are explanations for the unexpected low moisture level

in the second test series. Basically, these involve characteristics

of the soil that affect the drainage of water through the soil as

well as across its surface. A discussion of this phenomenon,

however, is beyond the scope of this study.

Impact Performance Data

The peak acceleration imparted to the test headform is the

impact performance measure used in this study. These data are

shown in figures 4 through 9. Figures 4 through 7 show the data

for each playground and both test series. Data obtained from

series 1 and 2 are depicted by the symbol 1 and 2, respectively.

From an examination of the test data, it appears that the trend of

the data can be approximated by the following equation:

Peak Accel. = x Drop Height +

where and <Z^ are constants to be determined from the test data.

This empirical relationship can be used to estimate the average

peak acceleration for a particular drop height. Also, the earlier

laboratory studies provide additional evidence to justify this

linear relationship. Therefore, each of these figures includes

the linear model obtained from a least squares fit of the data.

The data collected from playground 1 are shown in figure 4.

Although the average peak accelerations differed for the two test

series, this difference is probably not significant because the

differential is only on the order of 15 g's. The average moisture

contents and densities were also about the same for the two test

series. None of the drop tests at this playground produced peak

accelerations that exceeded the 200 g criterion. This level of

acceleration has been proposed for use in evaluating the impact

attenuation performance of playground surfacing materials.^/

Figure 5 shows the data collected from playground 2. The

first test series produced significantly higher peak accelerations

than obtained in the second series. The accelerations were consistently higher for corresponding drop heights and the average peak

accelerations differed by 40 to 60 g's. While none of the accelerations from the second series exceeded the 200 g criterion, the

soil conditions at the time of the first test produced peak

accelerations of 200 g's at a drop height of approximately 5.5

feet. This difference may be explained, in part, by the soil's

higher moisture content at the time of the second test series.

9
which was 14.4 percent versus 11.6 percent for the first series.

The effect that increased moisture in loose materials has on

improving their ability to attenuate impacts was consistently

demonstrated in the testing of sand and other loose materials in

the laboratory.

Figure 6 shows the data collected from playground 3. As with

playground 2, substantially higher peak accelerations were measured

in the first test series. Although not as consistent, the differential

exceeds 100 g's at the highest drop height. The average moisture

content was also higher at the time of the second test series (15%

versus 13.7%), but not to the extent that the moisture contents

differed at playground 2. The 200 g criterion was exceeded at

drop heights of approximately 4.5 feet and 8 feet for the first

and second series data, respectively.

The soil conditions (moisture/density) of playground 4 were

almost identical for both series of tests, as are the peak accelerations. Figure 7 shows these data. The differential in average

peak accelerations does not exceed 10 g's. Drop heights above 6

feet produced average peak accelerations in excess of 200 g's.

Peak accelerations observed in each of the eight sets of

tests (4 playgrounds, 2 series each) are shown collectively in

figure 8. The data from each set of tests are uniquely numbered.

The numbers 1, 2, 3, and 4 depict data from playground 1, 2, 3,

and 4, respectively, for the first series, and the numbers 5,6,

7, and 8 depict data from playgrounds 1, 2, 3, and 4, respectively,

for the second series.

The peak accelerations obtained from playground 3 (first

series) are clearly the highest. The density of that soil was

also higher than that of any of the other soils. However, the

soil density of playground 3 at the time of the second test series

was also the highest for that series, yet peak accelerations

obtained from that set (7) are lower than accelerations obtained

from one of the less dense soils (2)

Density alone, therefore,

does not correlate well with peak acceleration.

Regarding moisture content, there is evidence to suggest that

moisture has an effect on the impact attenuation performance of

some soil types. It is worth noting again that the two soils

having the least moisture, (2) and (3), produced relatively high

peak accelerations. However, a relationship between moisture

content and acceleration cannot be derived for these tests due to

the absence of sufficient variability in the moisture contents of the

four soils tested.

With regard to soil types, the absence of distinctive difference in the soils again masked possible differences in performance.

For example, the soil of playground 3 was predominantly a silt,

but also contained clay and sand components that were common to

the other three soils.

10
Peak accelerations measured during tests on the asphalt

surface are shown in table 4 . Each of the three drops resulted

in peak accelerations that exceeded 350 g's at a drop height of

0.43 foot.

Table 4 . Impact Attenuation Performance of Asphalt

Peak Acceleration Drop Height (ft)

1. 356 0.43

2 . 394 0.43

3 . 428 0.43

Comparison of Field and Laboratory Results

A comparison of field impact data to that obtained in the

laboratory tests of surfacing materials is given in figure 9. In

general, the soils impacted in this study produced peak accelerations which were greater than those produced by most loose materials

but considerably less than peak accelerations produced by asphalt,

synthetic turf, and pea gravel. A perspective of test conditions

must be maintained, however, when making these comparisons. The

soils were tested in-situ, and, consequently, the test conditions

(density, moisture, etc.) are those of a playground environment.

The loose materials were tested in the laboratory and were not

subjected to compaction, aging, or other conditions of playground

exposure. Consequently, better performance should be expected

from the materials tested in the laboratory. On the other hand,

the soils were not tested over a full range of naturally occurring

conditions. For example, the distinctive performance of playground

3 in the first test series appears to be related to its relatively

low moisture content. For still lower levels of moisture, there

is evidence that its ability to attenuate impacts would be further

reduced. From the data collected in this study, it is not evident

that the impact attenuation performance of a given soil v;ould

under different conditions, approach the poor performance of pea

gravel or asphalt.

V. SUMMARY

This study investigated the impact attenuation performance

of playground soils and asphalt. These soils and asphalt were

tested in-situ using a method of testing which was developed in

an earlier laboratory study of playground surfacing materials.

To facilitate mobility, the existing test apparatus was modified

and mounted onto a vehicle. An engineering firm specializing in

11
soil analyses was retained to assist in the selection of test

locations, to conduct tests of the soils, and to classify the

soils which were tested. Fourteen candidate sites were visited

within the Montgomery County park system, and, subsequently, five

playgrounds were selected—four for the purpose of testing soils

and one for testing asphalt. The soils which were tested comprised

four adjacent categories of the Unified Soil Classification

System.

Two series of tests, the first series conducted in September

and the second in October, provide the impact performance data.

These data were analyzed to identify possible correlations

between peak accelerations (the performance measure) and characteristics of the soil. Peak acceleration appears to be correlated

with a soil's moisture content; other associations are not

evidenced by the data. This is not surprising in viev/ of the

limited number of soils tested, the large number of variables

that characterize a soil, and the confounding of these variables

in the soils tested.

A comparison of the impact performances of soil and other

surfacing materials was made. This comparison showed that the

impact performances of these materials form three distinct groups.

Asphalt, synthetic turf, and pea gravel are materials that do not

attenuate an impact very well. Asphalt, which was tested in this

study, was the worst performer, producing an average peak acceleration

of 400 g's at a drop height of approximately 0.4 foot. In general,

the soils tested produced lower peak accelerations, but not as

low as most of the loose surfacing materials (6 inches in depth)

which were tested in the laboratory. However, a perspective of

test conditions must be maintained when making these comparisons.

The soils were tested in-situ, but none of the loose materials

were tested under conditions of a playground environment.

12
A. Monorail Support System

B. Typical Test Set-Up

FIGURE 1.

13
FIGURE 2.

14
100

I i_n

I r\

i_n

I

I IV'.

^ oo LiJ (SJ H

cnLd

Or— LO H 1 O H- </>

O r—

cr o

oo o CSI o

C/'J

LU C_J GO *— O

O)

Q

OO

O

rG)

CD

Q

LO

O G)

OO

G)

CM

Q. <</)</) H Z CD V)HUJ>LjJ

15

FIG.

3:

PARTICLE

SIZE

OF

THE

FOUR

PLAYGROUND

SOILS
200

!LU

u

CL, *0 CL aP

un

CT, • LO • • . ?}«

r

—1

LO CN CN 1 o O

cn rH ••

W rH •• rH OJ • cu • •H •H .. •H .. 4J

CO Li • w

L • cn

OC -H (U

G ‘H

W OJ 0 W 0) 0 • • Q S Q 2

rH•H • • • • 0 Cn Cn cn

Oj > > > > < < c c o

00

r-

<D

LO

CO

C\J

-u0Q4- 1—X

CDH

LdX

CLo

CLO

CLoH

CJ<

Q_XH

G) G>

CO (O

<S©O ^ CNJ ©

CL Ld < O

W0) ©

CO

16

FIG.

4:

SOIL

IMPACT

ATTENUATION

PERFORMANCE-PLAYGROUND
300

CL

u

u

CL C^P (L <if> 4J VO

(—

00 • ro • •H • (—1 • >5' >1 in CM (—1 CM r-l rH 1—

o (N o

r—1 >1 • • r-l •• 0) (1) cn • W • > >1 QJ • • -p (U .. 4J

tn (T3 •H • tS) •H • t/3 Li I—

Li c *H Ll

C -H

OU (U 0) 0 OJ Q) 0

in

Q cn

Q S

r—

. • . . •H IT> cn cr> 0 > > > >

in < < < <

O)

CO

CD

LO

"T

CO

(\J 0

<0 4-X

CDH

LiJ X

Q-O

(YQ

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h“

CJ<

CLH II

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(S <S> G>

O

LO G) LO

Q

(\J C\J

CL 1x1 < ^ WX

CD i 17

FIG.

5:

SOIL

IMPACT

ATTENUATION

PERFORMANCE-PLAYGROUND
350

TSc

(T3 cn

>1

0)>1 4J

ro I—I "H u cn

I—I H0w

PmU

Cl| 0>vO r'• • m

pH o

CO iH

CU •H

!h • 0) C

C/2 0) G 4-) CO •Hos

!T> 0^ > > < c

Pm <^iP U O G • in CM iH o

CO I—I •• OJ •HH • QJ C -H

cn (D 0 Q 2

pj' cn > > < <

-P

CO

CO

-4 r- — <D

LO

—— CO

M-)00

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CDHUX

0.ooo

I—u<

CLXH

CO

CM

(S G5 G) <S (S

G) LO (S LO o

CO (M CM

Q_ LlI < w

N,U> VH

18

FIG.

6:

SOIL

IMPACT

ATTENUATION

PERFORMANCE-PLAYGROUND
t. [h •H U u

'V CL CL afi c in w (T3 <Ti *0 CO • a C/J • • in 0 rH rH

(U >1 (H O CN o

u 0) rH • • rH • •

(13 >1 03 • 03 • U (T3 cu •• 4J 03 • • 4J •H rH •H • 0) H • 03 s u L c ’H L c •H

03 03 0

s

03 03 0

Oj Q C/3 Q

rH • • • • •H cn cn cn DT 0 > > > > C C C < O)

<M (M

\

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OJ

\

\

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\(\J (Nj

r

Ir

r

u

L

1

r

r

t

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IH

IL_

L

L

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-\ - t

<D

ID

CO

d)<D t+-

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H

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X

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CL

O

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19

FIG.

7:

SOIL

IMPACT

ATTENUATION

PERFORMANCE-PLAYGROUND
350

CD

00

<D

LO

'T

CO

C\J

-u04-

I—r

(DH

LjJ X

a.oao

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20

FIG.

8:

SOIL

IMPACT

ATTENUATION

PERFORMANCE-ALL

PLAYGROUNDS
350

21
APPENDIX A. SOIL ANALYSIS REPORTS

The results of the soil analyses reported by

AMBRIC Testing and Engineering Associates of Va., Inc.,

are included in this appendix. Specific identification

of the four playgrounds has been deleted from these

reports

.

22
AMBRIC TESTING dc ENGINEERING ASSOCIATES OF VA.. INC.

REGISTERED ENGINEERS

• INSPECTORS »

TESTING LABORATORIES

• CHEMISTS •

4110 Wheeler Avenue

Alexandria, Va. 22304

(703) 370-3100

Report No. NBS-I 2 October 1979

National Bureau of Standards

Building 220, Room A359

Washington, D. G. 20234

Attn: Mr, Wm. Beine

Re: Impact Study

Soil Sample Analysis

Purchase Order No. AB-9621

Gentlemen

We report results of our laboratory and field testing of soil

sampled on 17 and 18 September 1979. A preliminary visual site investigation was conducted on 11 September 1979 to isolate recreational

areas having distinct differences in soil classifications.

Dry density-moisture content tests

at the time of sampling with results as were taken at the

follows

above sites

Playground 1

Playground 2

Playground 3

Playground 4

107.9 pcf 0 14.37. £c 103.9 0 14.27.

103.8 pcf 0 12.07. 6c 101.7 0 11.1%

109.4 pcf 0 13.77.

104.9 pcf 0 15.07.

Laboratory analyses of the procured samples were performed in

accordance with applicable ASTM standards, and are enclosed.

Respectfully Submitte

D. D. Meisel, P.E.‘

Field Representative: David ?. Williams

S-4909

DFW/ano

23
AMBRIC TESTING & ENGINEERING ASSOCIATES OF VA„ inc.

REGISTEReO ENGINEERS

• INSPECTORS • TESTING LABORATORIES

• CHEMISTS •

4110 Wheeler Avenue

Alexandria, Va. 22304

(703) 370-3100

Report No, NBS-2 5 October 1979

Re: Impact Study - Field

Testing - Series II

Attn: Mr. Wm. Beine

Gentlemen:

National Bureau of Standards

Building 220, Room A359

Washington, D. C. 20234

We report results of our. field testing of soil at the four

subject sites on 4 October 1979.

Test 1 Test 2 Playground 1 102.5 pcf (? 14.3% 102.7 pcf 0 14.8

Playground 2 101.9 pcf 14.0% 102.6 pcf 0 14.7

Playground 3 106.9 pcf 0 15.3% 107.1 pcf 0 14.6

Playground 4 103.1 pcf 0 16.3% 106.0 pcf 0 14.6

Resoectfullv submitted.

B. H, Peebles, P.E.

Field Reoresentative : David F. Williams

S-4930

RMB/ano

24
AMBRIC TESTING & ENGINEERING ASSOCIATES OF VA., -mc.

National Bureau of Standards

Playground 1 Playground 2 Playground 3 Playground 4

]

Visual Description Reddish Brown

Silt

\ Light Brown

Gravel ley Clayey

Silt

Light Brown

Clayey Sandy

Silt

Multi-color

Micaceous Si.

Clayey Sand

,

Classification ML ML-CL

1 SM-SC SM

Sieve Analysis

i

’1

7, passing 3/4" 97.77. 91.8 100 100 7,

3/8' 95.37. 87.5 99.6 ,

'1 99.5% )

1

91.3 85.2 99.2

ii 98.2 ;

#10 86.2 83.2 94.6 96.5 1

#40 79.0 79.5 75.1 63.9 1

#80 75.3 70.5 59.6 43.2

#200 64.4 52.3 47.1 30.4

Atterberg Limits

j

Liquid Limit 32 21 19

1

Plastic Limit 27 15 16

Plasticity Index 5 6 3 N?

(

Maximum Density

(pcf)

115.3 117.3 121.3 104.8 i

i : _i —

Optimum Moisture 15.2 14.0 11.9

i

j 19.0

i

i

1

1

1

1 25

1

1

i

I

i

1

i ^ J
IT §f

5i

•VI I I NI

tU<ao-5 o2

oro

a.

lii <r.

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in ^ S'> rQ

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a. S

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u,o

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UiH-<Q

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tf*

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f~

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r-

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q: ui

r;i"y-TwPF (

r.trx

c7,ir
MOISTURE

-

density

RELATIONS

5

V*.

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< K

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r» o

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2

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X.3

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ce

<a

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ic

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7^

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o Aaci;^
APPENDIX B. SOIL CLASSIFICATION CHART

30
MAJOR DIVISIONS GROUP SYMBOLS

TYP 1 CAL NAMES

COARSE-GRAINED

SOILS

More

than

50%

retained

on

No.

200

sieve*

GRAVELS

50%

or

more

of

coarse

fraction

retained

on

No.

^

sieve

CLEAN GRAVELS

GW Well-graded gravels and gravel-sand mixtures,

little or no f 1 nes

GP Poorly graded gravels and gravel-sand mixtures,

little or no f i nes

GRAVELS WITHFINES

un Silty gravels, gravel-sands i 1 t mi xtures

GC

Clayey gravels, gravel -sandclay mixtures

SANDS

More

than

50%

of

coarse

fraction

passes

No.

4

sieve

CLEAN SANDS

SW

Well -graded sands and

gravel ly sands,

little or no fines

SP Poorly graded sands and gravelly

sands, little or no fines

SANDS WITH

FINES

SM Silty sands, sand-silt mixtures

SC Clayey sands, sand-clay mixtures

!?

'

'

'

1

FINE-GRAINED

SOILS

50%

or

more

passes

No.

200

sieve

•

SILTS

AND

CLAYS

Liquid

limit

50%

or

less

ML

Inorganic silts, very fine

sands, rock flour, silty or clayey fine sands

CL

Inorganic clays of low to medium piastici ty, gravelly

clays, sandy clays, silty

cl ays, 1 ean cl ays

OL

Organic silts and organic

silty clays of low piastici ty

SILTS

AND

CLAYS

Liquid

limit

greater

than

50% MH

Inorganic silts, micaceous

or diatomaceous fine sands

or silts, elastic silts

CH Inorganic clays of high

plasticity, fat clays

OH Organic clays of medium

to high plasticity

Highly Organi c Soi 1

s

PT Peat, muck and other highly

organi c soi 1

s

* Based on the material passing the 3-in. (75-mm) sieve. Fig. 1—Soil Classification Chart.

Reprinted/adapted, with permission, from the Annual Book

of ASTM Standards. Part #19/D2487. Copyright, American

Society for Testing and Materials, 1916 Race Street, Philadelphia, Pa. 19103.

31
CLASS 1 FI CATION CRITERIA

CLo

in

in

(U

C

o

c

o

m lA

in —

Ql O 03 O

</3 CO ^

U) £

-I ^ >.

CO CO c

03 Q- O U 3 O O 0) *D

*'u ~ ^60‘^'^10 Greater than 4

("30>^

C = r — Betv/een 1 and 3 z D,- X 0,

10 60

Not meeting both criteria for GW

O S) —

0 0—3 O <N in o* <N 0)

• O U

• o o

O 2 CN c Z O

m —

m m O w

m 03 2

a Q. ^ m

m

5^ rg 0) uA — Q. C C

03 03 <N X -C —

0) O 5^

-J 2 WA

Atterberg limits plot below "A" line

or plasticity index less than 4 Atterberg limits plottingin hatched area are borderline classifications

requiring use of dual symbol

Atterberg limits plot above "A” line and plasticity index greater than 7

~

^bO^'^lO Greater than 6

C = - 'V". Between 1 and 3 10 60

Not meeting both criteria for SW

Atterberg limits plot below "A" line

or- plasticity index less than 4 Atterberg limits plottingin hatched area are borderline classifications

requiring use of dual symbolAtterberg limits plot above "A" line and plasticity Index greater than 7

Visual -Manual Identification, See ASTM Oesicnaticn D 2488.

Fig. 1

Continued.

32
REFERENCES

1. Standard for Protective Headgear for Vehicular Users,

ANSI Z90.1, 1973, Ajrerican National Standards Institute, Inc.,

1430 Boradway, New York, New York.

2. Mahajan, B. M. , and Beine, W. B., "Iirpact Attenuation Perforinance

of Surfaces Installed Under Playground Equipirent," NBSIR 79-1707

February 1979.
NBS*114A (REV. 9-78)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIP. 80-2106

Niy.. J. Redtitent'$ Accession No- 4

4. TITLE AND SUBTITLE

SOIL IMPACT ATTENUATION PEPFORMANCE: A FIELD STUDY

5. Publication Date

S« P«formins Organization Code

7. AUTHOR(S)

VJilliam B. Beine and John R. Sorrells

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS fSrreer, City, Sfafa, ZIP)

Cansumer Product Safety OatTnission

5401 D^stbard Avenue

Bethesda, MD 20016

13. Type of Report & Period Covered Final

> -sty

‘

15. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-word or tesa factual summary of moat significant information. If document includes a significant bibliography or

literature survey, mention it here.) Irrpact attenuation performance tests v;ere conducted on the playing surface of

selected public playgrounds in r^ontgcmery County, Maryland, using a test method

developed in an earlier laboratory investigation of surfacing materials. Controlled

inpacts were obtained by dropping an instrumented headform in guided free-fall onto

the best surfaces from, various heights. The peak acceleration inpa<rted to the

headfcrm during impact was recorded as the performance parameter.

At four playgrounds, the tests were performed on the undisturbed soil underlying existing play equipment. At a fifth location, the asphalt surface of an

outdoor basketball court was tested. Soil samples from each playground were collected

analyzed and classified in accordance with standard methods prescribed by the ASU4.

Separate tests vere conducted following periods of dry and vet weather and on-site

measurements of soil density and moisture content were recorded at the time of tests.

Analysis of results indicated an apparent correlation between a soil's

performance and its moisture content; correlation with other soil characteristics

were not evident. The peak accelerations produced by the playground soils were much

lower than those produced by the asphalt surface but higher than those produced by

most loose materials previously tested in the laboiratory.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons)

Asphalt; irrpact att^uation;oeak. acceleration; ^playground safety; playground

su^aces; soil; surracmg materials ;^st meQiOdf^

18. AVAILABILITY r^Unlimited

I I For Official Distribution. Do Not Release to NTIS

I I Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SO Stock No. SN003-003-

I I Order From National Technical Information Service (NTIS), Springfield,

VA. 22161

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF

PRINTED PAGES

22. Price

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