Using a newly developed large ring-shear apparatus, a series of tests was conducted on silty soils to study their undrained shear behavior. The samples were made by mixing loess into a fine-graded silica sand with 10, 20, and 30% loess by weight. By performing tests at different initial void ratio, the undrained shear behavior of samples with different loess contents at loose and medium-dense states was presented and discussed. Basing on the tests results, effects of loess contents on the peak and residual shear strengths are examined. It was found that adding loess into the host sand could lower the peak and residual shear strengths; and these two strengths decreases with increasing loess content. Meanwhile, with increasing loess content, the dissipation of generated pore pressure from the shear zone becomes remarked slower when the shear box was turned into drained conditions, and there is little, if any, dissipation for tests on the mixture with 30% loess.
A fluidized landslide is usually characterized by high mobility and long run-out distance, and then followed by tremendous hazards. It is always the result of liquefaction, a process during which high pore water pressure is generated and soil mass loses a great part of its strength and shows the behavior of liquid. Therefore, research on this kind of failure has been mainly focused on liquefaction potential analysis with emphasis on the undrained shear behavior of soils. However, compared with those tests on clean sand, the undrained shear behavior of silty soils is less studied, although it has been pointed out that silt and silt-clay mixture are more prone to suffer from liquefaction failure with large resulting run-out distance, basing on many field observations (Bishop, 1973; Eckersley, 1990; Ishihara, et al., 1990; Zlatovic and Ishihara, 1995).