Strain softening constitutive model for the internal shear behavior of a Geosynthetic clay liner

A strain-softening constitutive model has been developed to model the internal shear load-deformation behavior of a hydrated, nonwoven fabric encapsulated and needlepunch reinforced geosynthetic clay liner (GCL) for use in performance-based design of geosynthetic barriers for waste containment. The softening formulation is based on a multiple yield surface model that employs an isotropic softening yield surface and a perfectly plastic yield surface to characterize post-peak strain softening and subsequent perfectly plastic behavior of geomaterials in a numerically stable manner. Model parameters are developed based on the results of large scale shear tests on GCL samples. The constitutive model has been implemented in a finite-difference software package for solution of geotechnical boundary value problems. The numerical implementation of the constitutive model compares well with the experimental data for uniform cyclic loading, capturing the unusual shape of pre-peak strength hysteresis loops and the softening in shear strength of the GCL beyond the peak shear strength. However, the model does not model the gradual cyclic degradation beyond the first or second cycle of loading and data is needed to test the performance of the model for non-uniform cyclic loading. The model applicable to both static and cyclic loading and can be used to model the performance of liner and cover systems that employ GCLs and are subject to waste settlement and seismic loading.