Undrained Responses of Reconstituted Saturated Soft Clay with Various Stress Paths

Abstract The loading stress path affects the soil’s dynamic response, but there are few previous studies on bidirectional shearing, let alone considering the influence of phase difference and bidirectional shear frequencies. This study investigates the undrained responses of reconstituted saturated soft clay under four typical shear stress paths using a multidirectional cyclic simple test system. All the soil samples are consolidated under normal vertical stress sheared in undrained conditions by applying two horizontal shear stresses acting along different directions from the consolidation stress. Test results indicate that soft clay’s dynamic strain, softening index, and dynamic strength depend significantly on the value of phase difference and the bidirectional shear frequencies: dynamic strength and softening index decrease while dynamic strain accumulates with increasing phase difference and decreasing bidirectional shear frequencies. An empirical formula is proposed to predict the development pattern of softening index versus load cycles under various shear paths based on test results. Practical Applications In this study, a series of simple shear tests was carried out under multidirectional shear paths, which may be helpful for field pile testing under cyclic loading. The simple shear tests all showed an increase in shear strain accumulation, owing to the change in shear stress path. This increase is undoubtedly smaller than the accumulation of lateral displacements in the pile tests because of the different boundary conditions and stress levels between the field and laboratory tests. Since soil behavior partly defines pile drifts, some models can also be validated at a small scale (element level) before investigating the pile–soil system. It is proposed that the simple shear test results can be used to calibrate numerical models for various stress paths.