Abstract: To accurately understand the mechanical properties of soil with large shear displacement, we examined the peak strength and residual strength of basalt residual soil under different shear modes and shear rates using ring shear apparatus to obtain the shear mode and the shear rate suitable for basalt residual soil, and on this basis analyzed the impacts of dry density and moisture content on peak strength and residual strength. Results unveil that specimens with existing shearing surface could reach residual strength state rapidly. As the results of pre-shear and multistage shear are large, we should select single-stage shear. Shear rate has a great influence on peak strength, but the influence on the residual strength is relatively small. Specimens under large shear rate would experience water leakage and soil squeezing, which is liable to cause deviation to the result. Moreover, with the increase of dry density, peak strength increases, while residual strength decreases first and then remains unchanged. The greater the water content, the smaller the peak strength and residual strength. Residual soil of basalt softens obviously when contacting with water. The research results offer reference for the stability analysis and treatment of basalt residual soil slope.

Key words: basalt residual soil, ring-shear test, shear rate, dry density, water content, peak strength, residual strength