The critical state behavior of saturated glacial till

A large number of glacial tills are distributed in the high and cold mountainous areas of the Qinghai-Tibet Plateau. Recently, climate change compounded by many other factors, promote the instability of glacial tills resulting in more frequent mountain disasters. Although the physical properties of glacial tills have been extensively studied in previous works, there are relatively few works that have focused on their shear behavior and critical state for different water contents. To understand the failure mechanisms, it is necessary to study the effects of water content on the shear behavior and critical state characteristics of glacial tills. This work discusses and studies the significance of compression, shear, and dilatancy of glacial tills in landslide prediction. The experimental results in this study are aimed to provide a basic understanding of the underlying failure mechanisms of glacial tills. Reconstituted specimens are studied through an oedometer, isotropic compression, and consolidated undrained shear tests. We compared the compressibility and shear behavior of glacial tills with three other types of weathered soils in Hong Kong: Lateritic soil (LAT), completely decomposed granite (CDG), and volcanic soils (CDV). Test results reveal similarities and differences between the tested soils. Through one-dimensional consolidation and triaxial compression tests, we find that the compressibility of glacial till is the lowest. Secondly, the stress-strain relationship exhibited by the glacial till is inconsistent with those of the other tested soils. Our test results showed that upon increasing the applied stress, glacial tills first softened and then hardened. Stress path analysis further showed that glacial tills first dilated and then shear contracted indicating a phase transition. In comparison, the other weathered soils consistently all shrink and eventually reach a critical state. The processes between soils are more complex. The slope and friction angle of the critical state line of glacial tills is significantly higher than that of CDG and CDV, but lower than that of LAT. This might be due higher large particle content of glacial tills and the difference in mineral composition.