Experimental and DEM study of monotonic and cyclic simple shear testing of an angular sand

Liquefaction of sandy soils under monotonic and cyclic shear loadings is responsible for numerous devastating failures of earth structures and hence represents a significant hazard. In this paper, cyclic and monotonic loading of an angular sand is replicated in the laboratory using a Cyclic Simple Shear apparatus and numerically using the discrete element method (DEM). For both the experiments and the DEM simulations, undrained conditions were attained by imposing a constant volume approach. A large series of tests, starting from an initial dense state and from two different effective vertical stress conditions, are performed. To obtain a comprehensive Cyclic Stress Ratio (CSR) - number of cycles to liquefaction diagram, from each of these initial states the undrained cyclic tests are conducted using three different shear load magnitudes. The three-dimensional DEM model developed is used to guide the interpretation of the experimental results and to investigate micromechanical processes involved during the cyclic shearing of the angular sand analogue as it approaches liquefaction. To interpret the results using the state parameter (ψ) concept, both drained and undrained monotonic simple shear tests were performed both experimentally and numerically to identify the critical state line.