Development of shear deformation due to the increase of pore pressure in a sandy model slope during rainfall

To examine the relationship between the increase of the shear strain and the volumetric water content, the suction, and the pore pressure in a slope under rainfall, an analysis of the measurement of the soil–water and the deformation of the sandy model slope due to rainfall infiltration is conducted. At first, the surface displacement of the slope mostly occurs due to the increase of the pore pressure. The surface displacement increases slightly under unsaturated conditions at first and later increases significantly with the increase of the pore pressure. The surface displacement increases slightly immediately after the generation of the pore pressure at first, and the ratio of the increase of the surface displacement to the increase of the pore pressure subsequently grows larger. The shear strain in the soil layer of the model slope also increases to a small amount with the increase of the volumetric water content or the decrease of the suction in unsaturated conditions at first and later increases significantly with the increment of the positive pore pressure. The relationship between the shear strain and the positive pore pressure is hyperbolic, and the maximum pore pressure is greater at a deeper layer.