Given the many variables as outlined previously, it takes considerable experience and judgment
in the selection of the undrained shear strength su to be used in Eqs. 6.39 and 6.40. The value of su
should be adjusted for the anticipated loss in shear strength as the cohesive soil is strained back and
forth during the earthquake. This weakening of the soil during the earthquake will be further discussed
in Sec. 13.5.