UFC 3-260-02

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.

L-12

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