Development Characteristics and Formation Mechanism of Chashushan Landslide in Batang, Western Sichuan

Abstract

Abstract:

Chashushan landslide is located in the intersection of Batang fault and Jinshajiang fault. With the complex geological structure and intense neotectonic movement, large landslides occur frequently in this area. Chashushan landslide originates from ancient landslide mass. The sliding deformation of the landslide first appeared in July of 2001, followed by creep deformation. Deformation velocity of the landslide was accelerating continuously because of deformation. Then a lot of distortion evidences appeared in the landslide mass. Finally, the landslide occured severely sliding on January 7,2006. The landslide is in unstable condition, and the deformation and failure of the landslide are obvious, and it is potential that the deformation and failure will last. Through field investigation, large-scale direct shear tests on slipping soils were carried out, then the shear strength was obtained under the condition of different water contents, which revealed the cohesion and internal friction angle decreased with the increase of water content. In this paper, based on the analysis of field geolo-gical survey, geophysical prospecting, drilling, and large-scale direct shear tests, the authors consider that the formation mechanism of Chashushan landslide is complicated: rocks affected by the fault structure have the intensive development of rock mass structures and poor mechanical properties of rock and soil masses; the stratum system of landslide has a hydrogeologic structure of groundwater rich in the upper and poor in the lower, which is very vulnerable to landslide disasters. The stability of the landslide body is in critical condition due to heavy rainfall. Canal water infiltration influence of freezing-thawing action induced the occurrence of landslide. FLAC^3D was used to simulate the stability of the landslide body. Results indicate that the landslide body has obvious signs of deformation under heavy rainfall and has formed intact slip surface, and the landslide is likely to occur again. Taking into account the formation mechanism of the landslide, it is effective for controlling the stability of the landslide body to strengthen the drainage and to avoid infiltration of the canal water.

Key words: Chashushan landslide, Batang fault, large-scale direct shear test, numerical simulation, formation mechanism

CLC Number:

P642.2
P694

REN Sanshao, GUO Changbao, ZHANG Yongshuang, ZHOU Nengjuan, DU Guoliang. Development Characteristics and Formation Mechanism of Chashushan Landslide in Batang, Western Sichuan[J]. Geoscience, 2017, 31(05): 978-989.

Figures/Tables 14

Fig.1 Regional tectonic setting of Chashushan landslide in Batang area

Fig.2 Distribution map of monthly average rainfall in Batang in the past years

Fig.3 Remote sensing map of Chashushan landslide

Fig.4 Engineering geological map of Chashushan landslide

Fig.5 High-density resistivity profile and engineering geological profile of Chashushan landslide

Fig.6 Typical photos of Chashushan landslide

Fig.7 Curves of shear stress and displacement with different water contents

Table 1 Strength parameters with different water contents

岩土体类型	密度/ (g/cm³)	含水率/%	内摩擦角/ (°)	粘聚力/ kPa
滑带土	2.09	7.47	36.5	31.28
滑带土	2.15	10.62	35.2	18.83
滑带土	2.27	12.73	27.6	32.27
滑带土	2.31	20.08	12.5	15.52

Fig.8 Curves of shear strength

Fig.9 Relationship curves of c and φ with water content

Fig.10 Satellite image of Chashushan landslide(according to Google earth)

Fig.11 Finite difference model of Chashushan landslide

Table 2 Values of mechanical parameters of rock and soil

编号	岩性	密度/(g/cm³)	体积模量/MPa	剪切模量/MPa	粘聚力/kPa	内摩擦角/(°)	泊松比
A	基岩	2.65	6.2×10³	3.5×10³	1 120	48	0.20
B	断裂带岩体	2.20	8.7×10²	6.1×10²	55	39	0.25
C₁	滑带土(自然)	2.13	6.5×10²	3.5×10²	31	32	0.28
C₂	滑带土(强降雨)	2.22	4.7×10²	3.1×10²	26	20	0.29
D	碎石土	2.05	7.3×10²	4.3×10²	23	28	0.28

Fig.12 Shear stress increment maps and X-displacement contour maps of Chashushan landslide under different conditions simulated by FLAC3D

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