Equation 3 becomes eq 1 if a resilient modulus
The New Hampshire Department of Transpor-
equal to 21 MPa (3,000 psi) is estimated for the A-
tation (NHDOT) is developing effective resilient
6 subgrade soil at the AASHO road test.
moduli values for typical subgrade soils found in
The effective resilient modulus is a single value
the state for use in the AASHTO design guide. The
that produces the same amount of annual dam-
soils selected for this project reflected most, but
age to the pavement structure when compared
not all, of the subgrade soils found in the state.
with the damage obtained from the use of seasonal
Resilient modulus tests were conducted on these
subgrade moduli. The relative damage ( uf)
soils at optimum density and as a function of tem-
(AASHTO 1996a) is calculated from
perature and moisture content. In addition, some
tests were conducted to determine the shear
uf = 1.18 108 Mr -2.32 .
(4)
strength properties of the soils. The shear strength
may be more critical for predicting damage than the
An example for estimating the effective resil-
resilient modulus during the spring thaw period.
ient modulus is shown in Figure 1.
This report provides the results from the exten-
30
0.005
Roadbed
Soil
Modulus
Relative
0.010
(psi)
Damage
20
MR
Month
uf
0.01
20,000
Jan
0.01
20,000
Feb
0.050
1.51
2,500
Mar
10
0.51
4,000
Apr
0.100
0.51
4,000
May
0.13
7,000
Jun
5
0.13
7,000
Jul
0.500
0.13
7,000
Aug
1.000
0.13
7,000
Sep
0.13
7,000
Oct
0.51
4,000
Nov
5.000
0.01
20,000
Dec
Summation: Σuf
10.000
3.72
13.000
1
Σu f
3.72
Average: u f =
=
= 0.31
n
12
Effective Roadbed Soil Resilient Modulus, MR (psi) = 5,000 (Corresponds to u f )
Figure 1. Chart for estimating effective roadbed soil resilient modulus for flex-
ible pavement designed using the serviceability criteria (after AASHTO 1996).
2
Previous Page
