Test study of influence of crack evolution on strength parameters of expansive soil

The strength parameters are obtained with consideration of influence of wetting and drying cycles by an experiment based on laboratory direct shear test. The test basically reflects the phenomenon of crack evolution with wetting and drying cycles and reveals that crack evolution results in strength degradation. The results show that both cohesion and internal friction angle will attenuate along with crack evolution. Comparatively, cohesion index will be affected more obviously by crack and its determination should be more cautious. The law of attenuation accords with hyperbola; and the empirical expressions are proposed, which show that the relationship between attenuation of shear strength with increase of wetting and drying times is in fact with crack evolution. The expansive soil in engineering practice includes all kinds of cracks; therefore, in the design, the selection of strength parameters should consider the crack in the expansive soils. As the same time, the test method proposed makes the research of influence of crack evolution on the strength characteristics relatively simple and feasible.