Deformation mechanism and stability evaluation of Dingjiapo landslide considering the matric suction of unsaturated soil

The rainfall-induced Dingjiapo landslide poses a potential threat to the safety of the proposed Yunyang to Kaizhou (Yunkai) expressway. In order to identify the characteristics of Dingjiapo landslide, field engineering geological mapping, drilling and tests are carried out, and a numerical simulation code Geo-studio in a fully coupled computing mode is used to analyze the variations of landslide seepage field, stress field and displacement field under different rainfall conditions. The role of matrix suction in landslide stability evaluation is analyzed and the landslide stability factors under different rainfall duration and rainfall intensity are estimated. The results show that the slope topography, loose soil and rock characteristics and potential free surface of slope determine the landslide formation and development, the permeability of the landslide body is relatively high and the rainfall stimulates the landslide deformation. The landslide is currently in a creep stage with a few fissures in the central and these fissures show signs of widening during the rainy season. Following the rainfall infiltration, pore water pressure rises, matrix suction declines, effective stress and shear strength also decline, and shear stress concentration occurs in the soil-rock interface, which causes strain and displacement of the slope and deformation and damage of the landslide. High-intensity short-term rainfall could rapidly infiltrate the shallow soil and induce a shallow slide in the saturated section. Low-intensity long-term rainfall can saturate the deep soil and cause a deep landslide with the soil-rock interface as a slip surface. The matrix suction has an important influence on the stability of soil landslide. The stability analysis results show that this landslide at present is in a basically stable state and the stability factor would drop in case of rainfall. The longer the rain lasts and the higher the rainfall intensity is, the lower the stability factor will be. The landslide I area has a greater impact on the safety of Yunkai Expressway than the landslide II area and more attention should be paid to the protection and treatment of the landslide I area.