Characteristics of the Sanmen Formation clays and their relationship with loess landslides in the Guanzhong area, Shaanxi, China

Abstract

Large, deep-seated landslides are one of the most common geologic hazards in the Loess Plateau of northwestern China, especially in the Guanzhong area of Shaanxi Province. To understand why these landslides occur, we conducted a field investigation, remote sensing image interpretation, and physical and mechanical tests. Geologic surveys have shown that the landslide deposits are composed of thick loess, river terraces, and the Pliocene Sanmen Formation and that the rupture surface is located in the Sanmen Formation clay. Test results suggest that the Sanmen Formation material has a high clay content (particle diameters < 1.95 μm) and a substantial proportion of expansive clay minerals such as smectite or illite-smectite. In addition to high activity and high water content, the clay is also characteristically weak with poor cementation and high expandability. The peak and residual strength values exhibit large differences under natural and saturated states. It is inferred that the strength of the Sanmen Formation clay greatly decreases when infiltrated by underground water. The clay then becomes a weak layer which forms shear zones. These shear zones are what control the development and distribution of landslides along the edge of the Loess Plateau. This study is important for understanding the occurrence of large-scale loess landslides and assessing urban natural hazards in the western Guanzhong area of Shaanxi.