SS9402-MN 950808ENGINEERING BULLETIN
Thickness Design for
Soil-Cement Pavements
PORTLAND CEMENT ~ ASSOCIATION
CONTENTS
Introduction Page
Quality Requireu]ents of Soil-Cemet]l
Basis for Thickness Design Procedure ......................... 3
Perforulance and Thickness of Favements in Service ............. 3
Results of Research Program ............................. 3
Basic Structural Properties ............................ 3
Load-Deflection Characteristics
......................... 4
Fatigue Properties
.................................. 4
Design Procedure
Subgrade Support .................................... $
Design Period
Traffic
ADT and Percent Trucks .................... i ...... 5
6
Projection
.......................................
Axle-Load Distribution
Fatigue Factor
Soil~ement Thickness
BJtu~nous Suffice T~ckness
Design Examples ............................ 7
....................................... 9
References ..........................................
Appendix A. Capacity Design ..................... 11
12
Appendix B. Basis of Design Charts and Fatigue Factor ............. 14
COVER PHOTOS: Soil-cement under construction in Gcnesee
County, Michigan, is shown in the top photo. At bottom right is a
soil-cement road, Route 259, in Florida.
Portland Cement Association 1970
This Engineering Bulletin was written by R. G. Packard of the Design
Research Section, Research and Development Division, Portland Ce-
ment Association. It is an extension of the research and analytical
studies of T. J. Larsen, P. J. Nussbaum, and B. E. Colley of the Divi-
sion's Pavement Research Section.
INTRODUCTION
The purpose of this bulletin is to provide engiueers with a
procedure for the thickness design of soil-cement roads,
streets, and parking lots. This special procedure has been
developed because soil-cement is a material that possesses
its owu unique structural characteristics.
Soil-cement pavements are designed both for economy
and long service life. The factors analyzed to determine the
design thickness are:
1. Subgrade strength
2. Pavement design period
3. Traffic, including volume and distribution of axle
weights (single- and tandem-axle loading configura-
tions of conventional tracks)
4. Soil-cement base course thickness
5. Bituminous surface thickness
Tbe design procedure is based on information from
several sources, including research, theory, full-scale test
pavements, and the performance of pavements in service. A
research program conducted by the Portland Cement
Associatioo correlates the design information from these
sources and results in a procedure developed uniquely for
soil-cement pavements.
OUAI. ITY REQUIREMENTS OF SOIL-CEMENT
Soil-cement is a mixture of pulverized soil, portland
cement, and water which, upon compaction and curing,
hardens'to form a durable structural material. Its compo-
nents meet specific mix design criteria,O)* and the
soil-cement pavements are coostructed under definite speci-
fications.(2,3)
The required cement content varies with soil type and is
determined by standard ASTM freeze-thaw and wet-dry
tests(4'$) and PCA weight loss criteria.O) For many soils,
the cement content to use can be quickly and easily
determined by the short-cut testing procedure.(Z )
The thickness design procedure in this bookIet relates to
all climate areas when tbe quality of the soil-cenreut meets
the above requirements.
BASIS FOR THICKNESS DESIGN PROCEDURE
Performance and Thickness of Pavements in Service
Since 1935 more than 85,000 miles of equivalent 24-ft.-
wide soil-cement pavements have been constructed. Tire
performance of tlrese pavements over thc years provides
valuable design information for the levels of thickness that
lrave been used.
Most of these pavements in service are 6 in. thick. This
thickness has proved satisfactory for the service conditions
of secondary roads, residential streets, and light-traffic air
fields. A few 4- and 5-in. pavements have beeu constructed
and have given good service under favorable conditions of
light traffic and strong subgrade support.
Many miles of 7- and 84n. pavements are in service on
primary and high-traffic secondary roads. Soil-cement
pavements with thicknesses of 9 in. or mom are not
numerous, although a few airport p[ojects have been built
with thicknesses of up to 15 in.
On Interstate highways in some of the comparatively
lighter traffic areas, wide ranges of soil.cement thicknesses,
from 4 to 12 in., have been incorporated into tbe total
pavement structures.
Valuable design information has also been obtained from
full-scale test roads and laboratory research conducted by
universities, highway departments, and the Po[tland Ce-
ment Association.
Results of Research Program
Studies at the Portland Cement Association laboratories
aimed toward the developmeot of a soil-cement thickness
design procedure covered these major pbases of research:
1. Basic structural properties
2. Load-deflection cbaractcristics
3. Fatigue properties
Basle structural propert/es
The structural properties of soil.cement depend on soil
type, curing conditions, and age. Typical ranges(6-9) for a
wide variety of soil-cements at their respective cetnent
contents required for durability arc:
Property 28-day values
Compressive strength, saturated
Modulus of rupture
Modulus of elasticity (static
modulus in flexure)
Poisson's ra tie
Critical radius of curvature
400-900 psi
80-180 psi
600,000-2,000,000 psi
0.12-O. 14'*
on 6x6x304u. beam 4,000-7,500 iu.
Over the design life of a soil-cement pavement the
average strength will be considerably greater than the
28-day values. Fig. I sbows 5-year laboratory strength gaius
for several soil-cements and Fig. 2 shows field-core strength
gains on four projects for various time periods. This
strcugth gum provides a nlargiu of safety in Ihe thickness
design procedure.
~'The critical radius of curvature is the radius at which a beam
fails due to a single load application. It is a measure of flexural
strength and may be compared to ultimate strain.
30aa
2500
~ooo
1500
5OO
days
3000
250o;
2000
1500
500
17yr
Fig. I. Stre.gth gabl with age, laboratory ~?)ecimens.
Fig. Z Strength gain with age, pro/ects in service.
Load-deflection characteristics
The load-deflection rescarchO o) on soil-cement pavements
showed that it was possible to describe tbc response by a
single equation, regardless of soil type and cement content,
as long as the final product met thc criteria* for fully
hardened soil-cement.
This research also demonstrated that thc strength of tim
pavement is more accurately assessed by the degree of
bending rather titan by deflection measurements alone. For
this reason, radius of curvature rather than defletztion was
used as a principal factor in evolving the design formula-
tions.
Fatigue properties
Thc fatigue studies(9) revealed that, for a given design, the
Table 1. Portion of AASHO Classification System Divided for Soil-Cement Design Procedure
Silt-clay materials
General classification Granular materials (more than 35 percent
(35 percent or less passing No. 200) passing No. 200)
A-1 A-2 A-7
Group classification A-3 [ A-4 A-5 A-6 A-7-5,
A-l-a A-l-b A-2-4 A-2-5 A-2-6 A-2.7 A-7-6
Sieve analysis,
percent passing:
No. 10 50 max.
No. 40 30max. 50max. 51 min
No. 200 15max. 25max. 10max. 35max. 35max 35max. 35max 36min. 36min. 36min. 36min.
Characteristics of
fraction passing No. 40:
Liquid limit 40 max. 41 min. 40 max 41rain 40 max. 41 min 40 max. 41 min.
Plasticityindex~ ___ 6max. NP 10max. 10max. 11min. 11min 10max 10max 11min. 11min,
Textural type for soil-
cement thickness design Granular soils Fine-grained soils
procedure
Table 2. Relationships Between Soil Types and Bearing Values
Typeof soil Subgrade BR range, R-value** range k-value range,
strength percent pci
Fine-grained soils in Low 3 to 6 20 to 30 100-150
which silt and clay size
particles predominate
Poorly graded sands Medium 7 to 10 30 to 45 150-220
and soils that are pre-
dominantly sandy with
moderate amounts of
silt and clay
Gravelly soils, well- High More than 10 45 or more 220 or more
graded sands, and sand-
gravel mixtures relative-
ly free of pla,~tic fines
Drn[a Bearing Ratio.
· * Resistance value determined by Stabilometer.
number of load repetitions to failure was related to tire
radius of curvature of bending. This relationship proved to
be similar to the known fatigue behavior of other materials.
The effect of soil type was significant in the fatigue
results. It required the division of soils into two broad
textural types-granular and fine-grained soils-and the
corresponding use of separate design charts for their
respective soil-cements. As shown in Table I, the two types
may be differentiated by the soil group classifications of
tire American Association of State Highway Officials as
follows:
1. Granular soils-Groups A-l, A-3, A-2-4, and A-2-5
2. Fine-grained soils-Groups A-2-6, A-2-7, A4, A-5,
A-6, and A-7
In further development of the design procedure, the
deflection, radius of curvature, and fatigue functions were
combined. Additional load tests were then conducted to
evaluate and establish parameters for the combined func-
tion. This analytical work is described in PCA Development
Department Bulletin D142.(6)
DESIGN PROCEDURE
Subgrade Support
Tile support given to thc soil-cement pavement by the
subgrade is a major elemeRt in the thickness design
procedure for soil-cement pavements. Subgrade support is
measured in terms of ibc Westergaard modulus of subgrade
reaction, k, aud is determiRed by plate-loading tests on the
subgrade. Procedures for field measurement of k-values are
given in Department of the Army Technical Manual
TM5-824-3 and discussed in a paper by Fordyce and
Yrjanson.( ~ 1 )
Where /ilne and equipment arc not available for deter-
mining the k-value by plate-loading, the approximate
relationships listed in Table 2 may be used as a guide; they
are based on laboratory tests or general subgrade soil type.
Since these relationships are approximate and often influ-
enced by variations in test methods, they may be modified
in accordance with local practice.
Very soft subgrades that have strength values signiti-
cantly less than the strength values shown in Table 2 will
,..not be able to support the compaction equipment necessary
,flor achieving adequate compaction for soil-cement. These
subgrades may be improved by several methods, described in
PCA's Soil-Cement Construction Handboolc (a )
Design Period
A design period of 20 years has been selected for use with
this procedure. It is not to be confused with the service life
of soil-cement pavements. Projects constructed in tile
middle and late 1930's show that their useful life has not
been exceeded; the soil-cement is still functioning as the
principal load-carrying layer.
Because the selection of thc design period is somewhat
arbitrary and the design formulation is not particularly
sensitive to variations in the design period, thc designer may
select a different value for tile design period and proportion
the total volume of traffic accordingly.
Traffic
The weights and volumes of axle loads expected during the
design period are major factors in determination of the
design th/ckness. The traffic analysis used in this procedure
involves:
1. Determining average daily traffic in both directions
(ADT) and the percentage of trucks
2. Projecting the traffic to a future design period
3. Delcrmining tile probable axle-load distribBtion
4. Computing the Fatigue Factor
5
Table 3. Yearly Rates of Traffic Growth and
Corresponding Projection Factors
Yearly rate of traffic
growth, percent
Projection factor for
20-year design period
1
2
2~
3
3'/=
4
5
5'/=
6
1.1
1.1
1.2
1.3
1.4
1.5
1.5
1.6
1.7
1.8
1.9
Table 4. Highway Capacity Guide
Capacity-average daily volume of
automobiles and trucks (two directions)*
Commercial
vehicles,
percent
Two-lane
rural
highways
Four-lane
rural
highways
Four-lane
urban
highways
0 5,750 19,250 37,500
10 5,200 17,500 34,000
20 4,800 16,050 31,000
*Thee are recommended capacities for design pu poses given n
Highway Capacity Manual.(3) Actual traffic counts show that the
capacity of e highway may be higher then the volume indicated.
]-lowcvcr, any other method* that gives reasooable esti-
mates of these traffic factors may be used.
ADT and percent trucks
Tire average daily traffic in both directions and the
percentage of trucks** may be obtained directly from a
traffic survey of the project, or data may be available from
the highway department or municipality for the specific
project or other prqiects carrying similar traffic.'['
Ifa 24-hour traffic count is made, it is conducted on one
*Methods of estimating traffic for capacity design are given ill
Appendix A. Capacity design, infrequently used for soil-cement
projects, may sometimes be appropriate for heavy-traffic-volume
situations. Other methods of estimating traffic are given in the PCA
publication Thickness Design for Concrete Pauernent$. (12)
**In this procedure the percentage of trucks includes all panets,
or more days between Monday and Friday. The 244~our
count is adjusted to average daily values. For guides in
making tlfis adjustment, the plannhig survey section of the
highway department may be consulted.~'?
Projection
Rates of traffic growth and corresponding projection
factors are used to estimate design ADTand the number or
trucks that will use the pavement during the design period.
The planniog survey sections of state highway departments
are very useful sources of knowledge about traffic growth
and projection factors. Their engineers determine these
factors for state highway projects and, in some cases, for
local roads and streets and other projects within their
states.
Table 3 shows relationships between yearly ~atcs of
growth and 20-year projection factors.$ Annual traffic
growth varies from about 2 to 6 percent, with the lower
values more applicable to the types of roads and streets
where soil-cmncnt is commonly used. The ltiglter growth
rates are for intercity and urbao highways.
For two4ane secondary rural roads and residential
streets where the principal function is land use or abutting
property service, the traffic growth rates may be well below
2 percent. For residential streets and light-traffic collector
streets, traffic growth is not great enougi~ to affect
thickness design.
For intermediate- to high-volume-traffic roads and
streets, a check on the design capacity of thc facility is
made to ensure that a sufficient number of lanes is provided
for the projected traffic. Table 4 may be used as a rough
check. Methods of designing for capacity traffic are given in
Appendix A.
Ax/e./oad distribution
Information on the axle4oad distribution for truck traffic is
needed to compute the numbers of single and tandem axles
of various weights expected during the design period. These
data are then used to compute the Fatigue Factor, which
expresses the pavement fatigue effects of the numbers and
weights of axle loads (see next page).
LOADOMETER DATA AVAILABLE
(Rural Roads and Urban Streets)
The axle-load distribution is computed with data from one
or more loadomcter stations or from W-4 tables for
appropriate classes of roads or streets. Recently some state
highway departments bare conducted Ioadometer surveys
for city streets and county roads. Minnesota, for example,
prepares W-4 "L" tables which show axle-load distribution
for traffic that is predmniuantly local. California has
~For other design periods, appropriate projection fac ors may
6
Table 5. Representative Fatigue Factors for Light-Traffic Pavements
Total trucks,* Heavy trucks,** Fatigue
Facility ADT percent percent Factort
(approx.) (approx.)
Purely residen- --
tial streets ~ 300 to 700 8 3 5 to 12
Residential col-
lector streets 700 to 4,000 8 3 12 to 20
Secondary roads Up to 2,000+ 14 to 20 5 to 8 12 to 30
mercial vehicles, including two-axle, four-tire vehicles.
· * Excludes panels, pickups, and other two-axle, four tire vehicles that are seldom
heavy enough to affect des[go thickness.
1These particular ranges of values for the Fatigue Factor are based on the
following characteristics of street and secondary road traffic: (1) one-half the
indicated number of heavy axle Ioads~ one direction; (2) axle-load distributions
varying from 12,000 to 20,000 lb. on individual axles; (3) weighted averages of axle
loads varying between 13,000 and 16,000 lb. on individual axles.
conducted similar surveys for streets carrying moderate to
heavy traffic volumes.
The procedure for use of a W4 table for a local road is
given in Design Example 1 on page 9. A W-4 table with the
essential data for the example is reproduced as Table 8 and
the computations are shown in Table 9.
For city street design, many communities have made
traffic studies based on a practical street classification sys-
tem. These studies indicate that streets of similar classifi-
cation carry essentially the same axle4oad distribution.
LOADOMETER DATA NOT AVAILABLE
(Residential Streets and Secondary Roads)
In many cases axle-load distribution data are not available
for the light-traffic category of pavements, i.e. residential
streets and secondary roads. In the absence of these data,
the values listed in Table 5 may be used to represent the
fatigue requirements for soil-cement pavement design as
they arc kuown to give reasonable design thicknesses.
For residential streets, traffic studies by WilsonO4)
indicate the traffic volumes may range as shown in Table 5,
with about 3 percent of the trucks heavy enough to affect
design thickness (12-kip axle loads and greater). For
secondary roads, the traffic volumes may range from very
Iow values up to an ADT of 2,000 or so, with about 5 to 8
percent of the trucks heavy enough to affect design. The
corresponding Fatigue Factors in Table 5 represent these
volumes of trucks with ranges of axle-load distributions
that are typical for streets and secondary roads.
For roads carrying unusually heavy axle loads such as
those of mining or logging trucks, it is necessary to obtain
the specific axle-load distribution and then to compute the
required Fatigue Factor.
LANE DISTRIBUTION
For four-lane as well as two-lane projects, it is assumed that
all lanes carry 100 percent of the one-directional truck
traffic. A more detailed analysis for four-lane projects may
be used to find the percentage of trucks in the right-hand
lane; however, this analysis usually will not significantly
change design thickness on a specific project.
Fatigue Factor
A single value that expresses the total fatigue consumption
effects of the volumes and weights of single- and tandem-
axle loadings for a given design problem is called the
"Fatigue Factor" in this design procedure. It is based on
coefficients showing the relative fatigue consumption of
different axle-load magnitudes, the "Fatigue Consumption
Coefficients," wlfich are listed in Table 6.* The designer
should note that different values are used for granular and
fine-grained soil-cements as specified by the two separate
equations developed from the reseamhl6) for the two
general soil types (see Table 1 ).
The Fatigue Consumption Coefficients are multiplied by
the numbers (in thousands) of axles in each weight group
and then summed to give a single-value Fatigue Factor, as
illustrated in Table 10 for Design Example 1.
S0ii-Cement Thickness
The thickness of the soil.cement base course is determined
by the use of Fig. 3 for granular soil-cement or Fig. 4 for
fine-grained soil-cement. The soil-cement thickness is read
to the nearest 1/10 in. by using the computed Fatigue
Factor and design k-value. This thickness is usually in-
creased to the next higher 1/2 in. unless there is an
adjustment for bituminous surface tlfickncss as explained in
the next section.
Bituminous Surface Thickness
Thc thickness of the bituminous surface depends on many
*The basis for computation of the Fatigue Consumption Coeffi-
cients and the Fatigue Factor is given in Appendix B.
7
Table 6. Fatigue Consumption Coefficients*
Axle
load, Granular Fine-grained
kips soil-cement soil-cement
Single axles
30
28
26
24
22
20
18
16
14
12
12,500,000.
1,270,000.
113,000.
8,650.
544.
27.
1.0000
0.0250
0.0004
3,530.
1,130.
337.
93.
23.3
5,2
1.0000
0.1600
0.0200
0.0018
Tandem axles
50 12,500,000.
48 3,210,000.
46 792,000.
44 186,000.
42 41,400.
40 8,650.
38 1,690.
36 305.
34
32
30
28
26
24
22
20
3,530.
1,790.
890.
431.
203.
93.
41.1
17.5
50.4 7.1
7.5 2.74
1.0000 1.0000
0.1200 0,3410
0.0120 0.1070
0.0010 0.0310
- 0.0081
- 0.0018
*Thsse coefficients express (he relative fatigue consump-
tion of different axle-load magnitudes and are derived
from Equations 25 and 25a for granular and fine*grained
soil-cernents, respectively, in PeA Development Depart-
ment Bulletin D142.(6} The basis for the computation is
given in Appendix B.
factors: the type of surfacing, the volume and composition
of traffic, climatic conditions, availability of materials, and
local practices. Table 7 is based on experience covering a
wide range of these variables and shows the surface
thicknesses recommended as good design practice. Under
favorable conditions indicated by previous local experience,
or where it is expected that surfaces may be sealed and
possibly resurfaced earlier than would normally be ex-
pected, the minimum thicknesses shown in Table 7 will be
adequate.
Research(e,~°) bas indicated that bituminous surface
thicknesses of under 2 in. do not appreciably add to the
structural capacity of the soil-cement pavement. However,
it is logical to assume that thicker surfaces, if used, would
contribute somewhat to the structural capacity. Although a
precise evaluation of the structural benefit of thicker
bituminous surfaciegs must await further research and
_o
6
I00 125 150 175 200 22:5
k- VALUE, PCI
Fig. $. Thickness design chart for granular soil-cements.
z
IO0 125 150 175 200 225
k- VALUE, PC I
F~g. 4. Thickness design chart for fine-grained ~oil-crtnc/it$.
Table 7. Bituminous Surface Thicknesses
Soil-cement Recommended Minimum bituminous surface
thickness, bituminous surface thickness, in.
in. thickness, in. Non-frost area Frost area
5-6 ~-1~ SBST* DBST*
7 1~-2 DBST 1 **
8 1~-2~ 1 1~
9 2 -3 2 2
'SBST, single bituminous surface treatment; Des'r, double bituminous surface treatment.
· ·Where snowplows are used. e minimum of 1~ in. is recommended.
performance experience, a structural allowance may be
made by using Fig. 5, which is based on the load-spreading
capacity of the surfacing.* For example, if Fig. 3 indicates
a basic soil-cement thickness of 7.8 in. and it is the local
practice to place a 3-in. surface, Fig. 5 shows that the
design soil-cement thickness could be reduced to 6.7 in.
This would usually be rounded to the next higher 1/2 in.,
i.e. 7 in. of soil-cement with a 34n. bituminous surface.
DESIGN EXAMPLES
Example 1
Project and traffic data
Local two4ane road (W-4 data available, Table 8)
Granular soil-cement
Weak subgrade, k = 125 pci
Design period = 20 years
Current ADT = 1,046
Projection factor = 1.5
Truck traffic** = 16 percent of ADT
Traffic ca/culations
DesignADT= 1,046 X 1.5 = 1,569
Truck traffic** = 1,569 X 0.16 = 251
Each way: 251/2 = 126
For design period: 126 X 365 X 20 = 919,800
In Table 9, the expected number of axle loads is
computed by multiplying 919,800 trucks by the axle loads
per 1,000 trucks given in the W-4 table, Table 8.
Table 10 shows the computation of the Fatigue Factor.
(Starting with the heaviest load categories, it will be seen
that fatigue effects diminish rapidly as loads decrease. This
*Fig. S was made by using an average value of ye + t in place of
N/~ in the design equations of PCA Development Department
Bulletin D142,(6) where a is the contact radius, computed at 6, 8,
and 10 in., and t is thickness of bituminous surface.
**Includes panels, pickups, and other two-axle, four-tire commer-
cial vehicles;
6 7 8
BASIC SOIL-CEMENT THICKNESS. IN.
F~g. 5. Design chart with soil-cement thickness reduced to allow for
thickness of bituminous ~arface.
usually makes it unnecessary to use the lower load
categories in the computations.) The total is rounded to
give the Fatigue Factor, 268,000.
Design thickness
As shown in Fig. 3, the basic soil.cement thickness required
for a k-value of 125 poi and a Fatigue Factor of 268,000 is
7.7 in. Table 7 gives the corresponding bituminous surface
thickness as 2 in.
Fig. 5 shows that, with a 2-in. surface, the soil.cement
tlfickness could be reduced to 6.9 in. Thus, a 7-in.
soil-cement base with a 24n. surface would be a practical
and economical design for this project.
Example 2
Project anti traffic tlata
Residential street (loadometer data not available)
Granular soil-cement
Weak subgrade, k = I00 pci
Current ADT = approx. 600
Projection factor = 1.1
9
Table 8. Axle-Load Data (Table W-4) for Local Stations in a Midwestern State*
Single-und trucks Tractor semi-trailer units Truck & trailer units 2-trailer units
Single- Tractor- All All 2- !
Axle loads Panel unit trailer truck- trailer ' Axles
in and Other Other 3-axle truck., 5-axle units, trailer 6-axle units, per
pounds pickup 2-axle, 2-axle, or prob- 3-axle 4-axle or prob- 4-axle 5-axle units 5-axle or prob- 1,000
under 4-tired 6-tired more able more able prob- more able vehi-
1 ton no. no. able no. cles"*
Under- 3,000 200 39 17 -- 1,967 -- -- 11 103 1,014.2
3,000- 6,999 48 29 130 6 1,088 -- 4 3 42 12 109 607.1
7,000- 7,999 -- 1 21 5 123 -- -- -- 60.3
8,000-11,999 1 1 40 12 256 1 2 7 66 157.6
12,000-15,999 -- 16 5 109 2 1 41 73.5
16,000-17,999 -- 5 22 -- 10.8
18,000-18,500 ' 1 2 18 - 8.8
18,501-19,999 2 9 - 4.4
20,000-21,999 3 13 ! 1 7 9.8
22,000-23,999
24,000-25,999
26,000-29,999
Tota~ single
axles weighed 250 70 238 28 -- 3 8 10 -- 23 --
Total single
axles counted 2,314 70 1,064 157 3,605 51 54 51 156 2,121 212
Tandem axle
Under- 6,000 - -- -
6,000-11,999 2 11 -- 4 21 15.7
12,000-17,999 8 45 2 6 44 43.6
18,000-23,999 5 28 1 3 22 24.5
24,000-29,999 3 17 -- 2 10 13.2
30,000-31,999 1 5 -- 1 5 4.9
32,000-32,500 -- - -- 1 5 2.4
32,501-33,999 3 17 -- 1 5 10.7
34,000-35,999 2 11 -- 1 5 7.8
36,000-37,999 3 17 -- -- 8.3
38,000-39,999 1 6 -- -- 2.9
40,000-41,999 1 1 12 5.9
42,000-43,999
44,000-45,999
'6,000-49,999
Total tandem
axles weighed 28 4 20 --
Total tandem
axles counted 157 157 27 102 129 -
Total vehicles
countedt 1,157 35 532 157 1,881 17 27 51 95 66 66
*Table W-4--([.) Number of axle loads of various magnitudes of loaded and empty trucks and truck combinations of each typeweJghed and
the probable number of such loads of each general type and of all types counted at (18) Ioedometer station{ during the period from June 15
to August 31. 1964.
· 'All single units and combinations.
tTotal single-unit and combination-unit vehicles = 2,042.
Traffic calculations
DesignADT = 600 X 1.1 TM 660
Assigned Fatigue Factor = 12 (as shown in Table 5 for
the higher range of HDT for residential strcets)
Design thickness
For a k-value of 100 pci and a Fatigue Factor of 12, Fig. 3
shows a basic soil-cement thickness requirement of about
5.9 io. Corresponding surface thicknesses raoge from 3/4 to
]0
Table 9. Typical Computations for Deter-
Axle
load
group,*
kips
(1)
mining Axle-Loac Distribution
Axles Axle
per loads in
1,000 design
trucks** periodt
(2) (3)
Single axles
20-22
18-20
16-18
14-16
12-14
10-12
Tandem axles
9.8
13.2
10.8
36.7
36.8
78.9
9,000
12,100
9,900
33,800
33,800
72,600
40-42 5.9
38-40 2.9
36-38 8.3
34-36 7.8
32-34 13.1
30-32 4.9
28-30 4.4
26-28 4.4
24-26
22-24
20-22
18-20
5,400
2,700
7,600
7,200
12,000
4,500
4,000
4,000
4.4 4,000
8.1 7,500
8.2 7,500
8.2 7,500
*When groups in the W-4 table~ Table 8,
exceed 2 kips, these groups ere proportioned
into 2 kip groups,
**Values for all single units and combina-
tions from the W-4 table.
tProducts of 919,800 trucks times column
(2) divided by 1,000.
1½ in. as stown n Table 7. Thus,an appropriate design for
constrdction would be a 6-in. soil-cement base course With
a Din. bituminous surface.
REFERENCES
1. Soil. Cement Laboratory Handbook, Portland Cement
Association, Skokie, 111., 1959.
2. Soil-Cement Construction Handbook, PCA, 1969.
3. Suggested Specifications for Soil-Cement Base Course,
PCA, 1969.
4. "Freezing-and-Thawing Tests of Compacted Soil-
Cemant Mixtures," ASTM D560-57, American Society
for Testing and Materials, Philadelphia, Pa.
5. "Wetting-and-Drying Tests of Compacted SoiI-Ccmcut
Mixt ures,"ASTM D559-57.
6. I.~irscn, T. J.; Nussbaum, P. J.; and Collcy, B. E.;
Research ot~ Thickness Design for Soil-Cement Pave-
Table 10. Typical Computations for Fatigue Factor
Axle / Axle loads Fatigue Fatigue
load, in design Consumption effectst
kips period.* Coefficient**
thousands
{1) (2) (3) (4)
Single axles
22 J 9.0 I 544.
20 12.1 27.
18 9,9 1.
16 33.8 0.025
Tandem axles
4,900.
327.
10.
I.
42 5.4
40 2.7
38 7.6
36 7.2
34 12.0
32 4.5
30 4.0
41,400.
8,650.
1,690.
305.
50.4
7.5
1.0
Total
Fatigue Factor
*Number from Table e, column (3), divided by 1,000.
· ' From Table 6 for granular soil-cement.
rProducts of columns (2) end (3).
223,600.
23,400.
12,800.
2,200.
600.
34.
4.
267,876
268,000
ments, PCA Development Department Bulletin D142,
1969.
7. Felt, Earl J., and Abrams, Melvin S., "Strength and
Elastic Properties of Compacted Soil-Cement Mix-
tures,'' ASTM Special Technical Publication No. 206,
1957, pages 152-178. Also, PCA Development Depart-
ment Bulletin D16.
8. Balmer, Glen G., "Shear Strength and Elastic Properties
of Soil-Cement Mixtures Under Triaxial Loading,"
ASTM Proceedings, Vol. 58, 1958, pages I187-1204.
Also, PCA Development Department Bulletin D32.
9. Larsen, T. J., and Nussbaum, P. J., "Fatigue of
Soil-Cement ," Journal of the PCA Research and Devel-
opment Laboratories, Vol. 9, No. 2, 1967, pages 37-59.
Also, PCA Development Department Bulletin D119.
10. Nussbaum, P. J., and Larsen, T. J., "Load-Deflection
Characteristics of Soil-Cement Pavements," llighway
Research Record, No. 86, 1965, pages 1-14. Also, PCA
Development Department Bulletin D96.
11. Fordyce, Phil, and Yrjanson, W. A., "Modern Design of
Concrete Pavements," Trans ortation En 't '
p gt ~eermg Jour-
nal, American Society of Civil Engineers, Vol. 95, No.
TE3, Proc. Paper 6726, Aug. 1969, pages 407-438.
12. Thickness Design for Concrete Pavements, PCA, 1966.
13.Highway Capacity Manual, Bureau of Public Roads,
U.S. Department of Commerce, Washington, D.C.,
1950, page 64.
14. Wilson, Roger E.,"Residential Traffic-Volmnes, Types,
Weights," 1965 Yearbook, American Public Works
Association, Chicago, Ill.
11
APPENDIX A. Capacity Design
For lfigh-traffic-volume projects it is sometimes necessary
to base the traffic volume on practical capacity, i.e. the
maximum number of vehicles per lane per hour that can
pass a given point under prevailing road and traffic
conditions without unusual delay or restricted freedom to
maneuver. Prevailing conditions include: composition of
traffic, vehicle speeds, weather, alignment, profile, number
and width of lanes, and type of area.
The term "practical capacity" is commonly used in
reference to existing highways and the term "design
capacity" is used for design purposes. Where traffic flow is
uninterrupted, or nearly so, practical capacity and design
capacity are numerically equal and have essentially the
same meaning. The term "design capacity" is used in this
booklet in accordance with AASHO usage, and design
capacities for various kinds of multilane highways are
summarized in Table Al.
ADT Capacity of Multilane Highways
For thickness design it is necessary to convert the passenger
cars per hour in Table Al to average daily traffic in both
directions, ADT. For multilane highways with uninter-
rupted flow, the following formula is used:
100P 5,000N
ADT =
100+r,n(/- O' KO
where P = passenger cars* per lane per hour (from
Table Al)
N = number of lanes-total both directions
Tph' = trucks, percent, during peak hours
I = number of passenger cars that occupy tire
same space as one truck, i.e. four in rolling
terrain and two in level terrain
K = design hour volume,DHV, expressed as a per-
centage ofADT; 15 percent is commonly used
for rural freeways and 12 percent for urban
freeways**
D = traffic, percent, in direction of heaviest travel
during peak irours-about 50 to 75 percent;
67 perceut is commmrly used for rural free-
ways and 60 percent for urban freeways
*See footnote for Table Al.
**See A Policy on Arterial Ilighway$ in Urban Area~, AASHO,
1957, pages 96-98, and J. J. Schuster and H. L. Michael, "Vehicular
Trip Estimation in Urban Areas," Engineering Bulletin of Purdue
Unieer$ity, Vol. XLVIII, No. 4, July 1964, pages 67-9:2.
Detailed discussions of this formula will be found in the
AASHO publications A Policy on Geometric Design of
Rural tlighways (1964) and A Policy on Arterial tlighways
in Urban Areas (1957).
Capacity of Two-Lane Highways
Important factors in the design capacity of two-lane
highways are: (I) the percent of total project length where
sight distance is less than 1,500 ft., and (2) lane widths of
less than 12 ft.']' The design capacity in vehicles per hour
for uninterrupted flow on two-lane highways is shown in
Table A2.
It is good practice to use both traffic projection factors
and design capacity for thickness design of specific projects.
Design capacity should not be used where it shows a greater
ADT than shown by traffic projection.
practice, except for very lightly traveled two-lane roads where land
service is a primary function,
12
Table Al. Design Capacities for Multilane Highways
Type of highway
Urban freeways with full access control
(30 to 35 mph)
Suburban freeways with full access control
(35 to 40 mph)
Rural freeways with full or
partial access control
Rural major highways with moderate
cross'traffic and roadside interference
Rural major highways with considerable
cross traffic and roadside interference
Design capacity-
passenger cars*
per 12-ft. lane
per hour
1,500
1,200
1,000
700-900
500-700
*Also includes panels, pickups, and other four-tire commercial vehicles
that function as passenger cars in terms of traffic capacity. VaJues are
taken from two AASHO publications, A Policy on Geometric Design of
Rural H~qhwey$ and A Policy on Arterial Highways in Urban Areas.
Table A2. Design Capacities for Uninterrupted Flow on Two-Lane Highways*
Design capacity, both directions, in vehicles per hour**
Alignment, where: L = (ane width, feet
percent of total Tph = trucks, percent, in peak houri
project length with
sight distance
Terrain of less than L = 12 L = 11 L = 10
1,500 ft. Tph = Tph = Tph =
0 10 20 0 10 20 0 10 20
0 900 780 690 770 670 600 690 600 530
Level 20 860 750 660 740 640 570 660 580 510
40 800 700 620 690 600 530 620 540 480
0 900 640 500 770 550 430 690 500 390
40 800 570 450 690 490 380 620 440 340
Rolling 60 720 510 400 620 440 340 550 400 310
80 620 440 350 530 380 300 480 340 270
'Source: AASHO'$ A Policy on Geometric Design of Rural Highways, Table II-1 O, page 88.
· 'Tabular values apply where lateral clearance is not restricted. Where clearance [$ less then 6
ft.. apply values given in Table I1-11 of the above-cited publication, page 89.
t C)oes not include tour-tire vehicles.
13
APPENDIX B. Basis of Design Charts and Fatigue Factor
The design procedure given in this bookleL is based on the
formulations described i't PCA Development Department
'Bulletin D142.(6) The procedure has been developed
further so that the same result is obtained in a more direct
manuer. The purpose of tiffs appendix is to explain how the
original formulations are applied in the design procedure.
Equations 25 and 25a in the research report give the
allowable number of load repetitions in the form
IV = elf(h) J \i, /
whereN = allowable number of load repetitions
kg = Westergaard's modulus ofsubgrade reaction,
pounds per cubic inch
A ~ = an exponent-0.3 for granular mil-~ements
and 0.315 for fine-grained soil-cements
A2 = an exponent-40.0 for granular soil-cements
and 20.0 for fine-grained soil-cements
C = a constant- 10.4 for granular soil-cements
and 10.0 for fine-grained soil-cements
./(h) = (2.lb - 1)2 where h is thickness, inches
il1.5
a = radiusofload contact area, inches
P = wheel load, kips
The total faligue consumption of the expected nmnber
of axle loads, hi, of various magnitudes, Pi, can be
expressed as
fatigue consumption = ~/Vt.
Substituting for N, thc equation becomes
ni
fatigue consumption= ~ [(1.77kg~4
Lf(h) (i .77kg)A ' 2( i) 'hi
In the summation, dividing by an arbitrarily selected
(P,/~)Aa (in this case for an 18-kip single-axle load or a
9-kip dual-wheel load) and multiplying this term outside
the summation,
fatigue consumption = If( C 1-42 (P.IA:~
h) (1.77kg)A 'J \x/~ ~]
In Table 6 the Fatigue Consumption Coefficients, Fi,
represent the values of
The Fatigue Factor, T, represents the sununation, i.e.
T = ~Ft~zi
Setting htigue consumption equal to 100 per~nt, the
fatigue ~nsumption computation procedure can be ex-
pressed as
From this equation the des~n curves iu Figs. 3 and 4 were
constructed. The result is that the designer may read the
thickness, h, directly from the curves for a given kg and T,
avoiding the selection o~ trial thic~esses that g~ve frac-
tional fatigue consmption.
Bemuse the values of A~, A2, and C are different for
granular and fine,rained soil-cements, separate dcsi~
charts and Fatigue Consumption Coefficients are required.
14
This publication is based on the facts, tests, and authorities stated
herein. It is intended for the use of professional personnel competent to
evaluate the significance and limitations of the reported findings and
who will accept responsibility for the application of the material it
contains. Obviously, the Portland Cement Association disclaims any
and ail responsibility for application of the stated principles or for the
accuracy of any of the sources other than work performed or informa-
tion developed by the Association.
KEY WORDS: axle loads, base courses, fatigue, layered system, radius of
curvature, roads, soil-cement, streets, structural design, thickness, traffic.
ABSTRACT: Presents a procedure for thickness design of soil-cement roads,
streets, and parking Iots. Design variables are soil subgradc support and tire
volumes and weights of axle loads expected during the design period. Thc
procedure is based on research results and performance experience.
REFERENCE: Thickness Design for Soil-Cement Pavements (EB068.01S),
Portland Cement Association, 1970.
'i