Multidirectional cyclic shearing of clays and sands: Evaluation of two bounding surface plasticity models

Seismic site response analysis (SSRA) is typically performed considering only one horizontal component of earthquake excitation. In many cases, however, two or three components are needed for the analysis to properly account for the true multidirectional nature of seismic loading. In this type of analysis, it is essential to use multiaxial constitutive models that can realistically describe the stress-strain response of soils. Development and validation of such constitutive models are essential steps toward this goal. Fortunately, a large quantity of experimental data from multidirectional cyclic shear tests is available and can provide physical basis for validating such models. This paper focuses on evaluation of two members of the SANICLAY and SANISAND families of constitutive models for simulating the response of clay and sand, respectively, when subjected to multidirectional cyclic shearing. The models have anisotropic elasto-plastic formulation, within the framework of critical state soil mechanics, and follow the bounding surface plasticity theory. They are calibrated and evaluated against experimental data on Gulf of Mexico clay and Monterey No. 0/30 sand in undrained multidirectional cyclic shear tests, including linear, circular/oval, and figure-8 loading paths. This study provides a basis for evaluation of the capabilities of these models in multidirectional shearing, thereby paving the way towards future applications in multidirectional SSRA.