structural design of highway pavement .ppt

a complete guide about highway design

1. Structural Design of
Highway
Third Stage
Lecture 8
Lecture. Dr. Rana Amir Yousif
Highway and Transportation Engineering
Al-Mustansiriyah University
2017

2. References:
1. Nicholas J. Garber and Lester A. Hoel.”Traffic and Highway
Engineering”, Fourth Edition.
2.Yoder; E. J. and M. W. Witczak, “Principles of Pavement Design”, A
Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A.,
1975.
3. Yaug H. Huang, “Pavement Analysis and Design”, Prentic Hall Inc.,
U.S.A., 1993.
4.“AASHTO Guide for Design of Pavement Structures 1993”,
AASHTO, American Association of State Highway and Transportation
Officials, U.S.A., 1993.
5. Oglesby Clarkson H., “Highway Engineering”, John Wiley & Sons
Inc., U.S.A.,1975.

3. Various empirical tests have been used to determine the material properties for
pavement design . Most of these tests measure the strength of the material and are not
a true representation of the resilient modulus. An extensive study was made by Van Til
et al. (1972) to relate the resilient modulus and other test parameters to the soil
support value or the layer coefficient employed in the AASHO design equation .
These correlations can be used as a guide if other, more reliable, information is not
available . It should be noted that any empirical correlation is based on a set of local
conditions . The correlation is not valid if the actual conditions are different from
those under which the correlation is established . Therefore, great care must be
exercised in the judicious selection of the resilient modulus from these correlations.
Correlations with Other Tests

4. Subgrade Soils Figure 7 .10 shows a correlation chart that can be used to estimate the
resilient modulus of subgrade soils from the R value, CBR, Texas triaxial classification,
and group index.
FIGURE 7 .10 Correlation chart for estimating resilient modulus
of subgrade soils (1 psi = 6.9 kPa ) . (After Van Til et al. (1972) .

5. The R value is the resistance value of a soil determined by a stabilometer. The
stabilometer test was developed by the California Division of Highway sand
measures basically the internal friction of the material ; the cohesion for bonded
materials is measured by the cohesiometer test. Figure 7 .11 is a schematic diagram
of stabilometer, which is a closed-system triaxial test. A vertical pressure of 160 psi
(1.1MPa) is applied to a sample, 4 in . (102 mm) in diameter and about 4 .5 in.
(114 mm) in height, and the resulting horizontal pressures induced in the fluid
within the rubbe rmembrane are measured.
R Value :

6. The resistance value is computed as
in which R is the resistance value ; pv is the applied vertical pressure of 160
psi (1 .1 MPa); ph is the transmitted horizontal pressure at p.S, of 160 psi
(1 .1 MPa) ; and D2 is the displacement of stabilometer fluid necessary to
increase horizontal pressure from 5 to 100 psi (35 to 690 kPa), measured in
revolutions of a calibrated pump handle . The value of D2 is determined after
the maximum vertical pressure of 160 psi (1 .1 MPa) is applied . If the
sample is a liquid with no shear resistance, then ph = pv, or from Eq . 7 .5, R
= 0. If the sample is rigid with no deformation at all, then ph = 0, or R = 100.
Therefore, the R value ranges from 0 to 100. To ensure that the sample is
saturated, California used an
exudation pressure of 240 psi (1 .7 MPa), whereas Washington used 300 psi
(2.1 MPa) .

7. The California Bearing Ratio test (CBR) is a penetration test, wherein a
standard piston, having an area of 3 in . 2 (1935 mm2 ), is used to penetrate
the soil at a standard rate of 0 .05 in . (1 .3 mm) per minute . The pressure at
each 0 .1-in . (2.5-mm) penetration up to 0 .5 in . (12 .7 mm) is recorded and
its ratio to the bearing value of a standard crushed rock is termed as the CBR.
The standard values of a high-quality crushed rock are as follows :
CBR

8. The group index, which ranges from 0 to 20, is used in the AASHTO soil
classification system . The values vary with the percentage passing through a
No. 200 sieve, the plasticity index, and the liquid limit and can be found from
charts or formulas.
Other Correlations
In addition to Figure 7 .10, other correlations between MR, CBR, and R
values are also available . These correlations could be quite different from
those shown in Figure 7 .10 .
Group Index

9. in which MR is the resilient modulus in psi . The coefficient, 1500, could vary from 750 to 3000, with a factor
of 2. Available data indicate that Eq. 7 .6 provides better results at values of CBR less than about 20. In other
words, the correlation appears to be more reasonable for fine-grained soils and fine sands than for granular
materials.
The Asphalt Institute (1982) proposed the following correlation between M
R and the R value :
Laboratory data obtained from six different soil samples were used by the Asphalt Institute (1982) to illustrate
the relationships, as shown in Table 7 .4 . The R values were obtained at an exudation pressure of 240 psi (1 .7
MPa). The CBR samples were compacted at optimum moisture content to maximum density and soaked
before testing . The repeated load triaxial tests were performed at optimum conditions using a deviator stress
of 6 psi (41 kPa) and a confining pressure of 2 psi (14 kPa) .
It can be seen from Table 7 .4 that the equations for estimating MR from CBR and R values have a very
limited range . The resilient moduli estimated from CBR values of 5.2 and 7 .6 and R values of 18 and 21
generally conform to the guidelines for accuracy within a factor of 2. Estimates from CBR values of 25 or
higher and R values above 60 would appear to overestimate MR by Eqs. 7 .6 and 7.7.
It should be noted that the MR of granular materials increases with the increase in confining pressure, and that
of fine-grained soils decreases with the increase in deviator stress . Therefore, a large variety of correlations
might be obtained, depending on the confining pressure or the deviator stress to be used in the resilient
modulus test .

10. Figure 7 .13 shows the relationships of the layer coefficient , Marshall stability,
cohesiometer values, and resilient modulus .
Hot Mix Asphalt

11. In the AASHTO design method, the quality of the HMA, base, and subbase is indicated by their
structural layer coefficients. These correlation charts were originally developed to determine the
layer coefficients, but can also be used to determine the resilient modulus. More about layer
coefficients is presented in Section 11 .3 .4 .
Example 7.4:
Given CBR values of 30 and 80, determine the corresponding R value, Texas classification, and
resilient modulus when the materials are used as a base course, a subbase course, and a subgrade.
Solution: The correlations for base, subbase, and subgrade can be obtained from Figures 7 .15a ,
7 .16, and 7.10 . The results are tabulated in Table 7 .5. It can be seen from Table 7 .5 that the
correlations among CBR, R value, and Texas classification are practically the same no matter
whether the material is used as a base, a subbase, or a subgrade . This is not true for the resilient
modulus, where a large variation exists. This is reasonable, because the resilient modulus
depends on the state of stresses, which varies with the location where the material is to be
placed .
Structural Layer Coefficient