In regions where large moisture variations, freeze and thaw, etc., will affect the
strength of the subgrade soils and subgrade, AASHTO provides a procedure to modify
the composite modulus of subgrade reaction. Table 3.22 provides a worksheet, and
Table 3.23 shows an example. The seasonal variation in strength is determined using
laboratory procedures or nondestructive testing (NDT). The seasonal strength of the
subbase and subgrade is entered in columns 2 and 3 of Table 3.22. The composite
modulus of subgrade reaction is determined using Fig. 3.11 and entered in column 4.
If a rigid foundation is present within 10 ft (3 m) of the surface, the k value is corrected