Energy-Based Method for Analyzing the Collapse Characteristics of Silt Subjected to Changes of Principal Stress Orientation

When soils are subjected to dynamic loadings, their stress states not only alter in stress ratios but also in principal stress orientations cyclically. Under these complicated stress paths the pore water pressure of soils may develop to the level of damage due to liquefaction even at a relatively low shear stress ratio. Therefore, to investigate the characteristics of pore water pressure buildup under such stress paths, a series of experiments were conducted with hollow cylinder apparatus. The samples are saturated silt from the sea entrance of Yangtze River with the relative density of 70% and 30%. The tests employed three kinds of cyclic loading schemes including changes of principal stress orientation (i.e. cyclic triaxial, torsion shear and principal stress rotation tests). According to the testing results, the dissipation energy (accumulated shear work per unit volume) was calculated for each sample. Based on it, the influences of cyclic stress ratio, frequency, relative density and cyclic stress path on the pore water pressure buildup were analyzed. In light of the concept of collapse, the collapse energy was proposed as a dynamic strength criterion. Subsequently, an energy-based pore water pressure model was proposed, whose parameter could reflect the collapse energy.