Formation Mechanism of No.1 Part Slide of Huangtupo Landslide in the Three Gorges Reservoir Area

Huangtupo landslide is one of the four largest landslides in the Three Gorges Reservoir area, where the Badong field laboratory is built by Three Gorges Research Center for Geo-hazards, Ministry of Education because it is typical and significant. The geological structure characteristics and formation mechanism of Huangtupo landslide can be clarified by exposing slope structure through the test tunnel excavation. Up to now, the geological structure of No.1 part slide exposed by the test tunnel excavation yield the following results: (1) In the bedrock of the No.1 part slide, the incompetent interlayers develop widely. (2) The excavation of the main test tunnel and the No.3 subsidiary test tunnel reveal that the displaced materials are composed of reddish brown mudstone and siltstone gravels, gray marlite and limestone gravels, and various crack strata. The ground water of the displaced materials is rich and the amount of water seepage is large. (3) The surfaces of rupture develop along the incompetent interlayers and the contacting surface between the stratum and the soil. The distribution of the surfaces of rupture in plane is very close to that obtained in previous studies. However, there exist some differences in the depth of the rupture surfaces. (4) The displacement monitoring data of deep boreholes show that there are creep displacements at the incompetent interlayers and the contacting surface between the stratum and the soil. Therefore, it can be concluded that the No.1 part slide crept along the incompetent interlayers and the contacting surface between the stratum and the soil under the long-term influence of tectonism and gravity, and the No.1 part slide has several surfaces of rupture.