A new simple shear apparatus and testing method for unsaturated sands
This paper deals with a new simple shear apparatus for the investigation of mechanical soil behavior of unsaturated coarse-grained soils under monotonous and cyclic loading conditions. Non-cohesive soils, such as sands, typically encounter low capillary effects, and little research has been dedicated to them so far. This holds true especially for effects of repeated loading. The presented test setup allows control of small matric suction up to 85 kPa within the soil specimens with the help of a vacuum control method. Although the pore water pressures are negative as occurring in nature, the pore air pressure is kept at an atmospheric level. Depending on the pore water drainage condition of the specimen boundaries, either drained constant suction tests (CS-tests) or undrained constant water content tests (CW-tests) can be performed. The focus of the research is placed on the interaction of loading and volume change with matric suction and degree of saturation, i.e., the hydraulic-mechanical coupling, during monotonous and cyclic shear. Central questions are the impact of matric suction and degree of saturation on the densification behavior as well as, vice versa, the effect of cyclic loading on a change of matric suction and degree of saturation. The new simple shear apparatus and testing method will be explained, their benefits and shortcomings will be discussed, and selected results of a series of tests will be presented.
Simple shear testing