30 June 2001
value of the sum of the principal stresses due to overburden is 0.045 MPa (6.5 psi). Using the
100,000 strain repetition curve from Figure L-9, the value obtained from Figure L-8 is added to all
values of the sum of the principal stresses indicated in the relationship and the adjusted curve is
replotted (Figure L-10). The result of adjusting the original relationship is to shift it to the right of
its original position. In Figure G-10, the results of laboratory resilient modulus tests on specimens
of the subgrade soil are also shown. From the intersection of these two relationships, a design
modulus MR of 103 MPa (15,000 psi) is determined.
e. Special Considerations. In some situations, the laboratory curve may not converge with
the limiting stress-modulus relationship within the range of values indicated. Obviously, two
possibilities are involved in this situation: the laboratory relationships could plot above or below the
limiting criteria curve. In the former case, since all values of the sum of the principal stresses
indicated by the laboratory curve would exceed the stress criteria within the region under
consideration, the value of 207 MPa (30,000 psi) should be used for the subgrade modulus. In the
latter case, the initial design thickness value should be increased and the limiting criteria curve
readjusted until convergence with the laboratory relationships is obtained.