Strain Energy, Yielding and Undrained Shear Characteristics of High Plasticity Compacted Clay Subjected to Stress Anisotropy

This experimental study investigates the effect of K₀, anisotropic and isotropic consolidation stress paths on the undrained mechanical response of compacted high plasticity clay. This type of soils is being used for the construction of the core structure in the earthen embankment dams. Therefore, undrained soil properties in saturated state are essential to obtain for the stability analysis and design of certain conditions, such as rapid drawdown case. The actual consolidation system prevailing in the field is anisotropic in nature, and it is necessary to take that into account for the determination of strength and yielding criteria of the soil. However, this effect of the consolidation system has not been studied in detail for high plasticity clay in a compacted state. A series of consolidated undrained triaxial compression and extension tests were carried out on compacted high plasticity clay with different consolidation stress ratios (K_c = σ_h′/σ_v′  = 0.70 to 1.00) and stress history (OCR = 1 to 10). Results indicated that the normalized undrained shear strength reduced with anisotropic consolidation, and its relationship with consolidation stress ratio (K_c) was found linear at each OCR levels. The reduction in strength was observed highest for extension loading condition at normally consolidated state. Strain energy dissipation response displayed that the governing strain energy mechanism shifted from volumetric to shear strain energy, as consolidation state changed from anisotropic to isotropic. Based on the obtained yield surfaces, pre-failure shear behaviour of soil was found predominantly elastic for compression loading and elasto-plastic for extension loading conditions.