SHEAR STRENGTH OF PRESTRESSED COHESIVE SOILS.

In situ tests using the Borehole Shear Test indicate that the increase in drained shearing strength of cohesive soils resulting from preloading is a function of the preloading stress ratio. This relationship is similar to the one that exists between normalized undrained shearing strength and overconsolidation ratio. The magnitude and rate of the increase in strength is seen to be varied, and probably depends on the initial shearing strength and the deformation characteristics of the soil under constant preload stress. Results for a number of cohesive soils indicate that all behaved in a similar manner, displaying hysteresis leading to increased cohesion and decreased friction angle as a result of preloading.