Redai dili (Oct 2022)
Formation Mechanism and Prevention of No.3 Landslide in Fei'e Mountain, Shunde District, Foshan City
Abstract
Landslide No.3 in Fei'e Mountain is located in the Shunde District of Foshan City, Guangdong Province, and its' lithology is mainly composed of pre-Cretaceous Baizushan Formation (K1b) argillaceous siltstone. In this study, engineering geological drilling, geophysical exploration, geological mapping, and indoor testing were used to determine that it is a medium-scale bedding rocky landslide with a typical double-layer deep sliding surface. The maximum length of the landslide body is approximately 220 m in the longitudinal (south-west) direction and approximately 230 m in the horizontal (north-west) direction; the maximum thickness is approximately 32m, and the attitude of sliding surface is 230°∠12°-17°. Landslide body tensile cracks, including nine large-scale tensile cracks, are very well-developed. The longest crack is approximately 120 m long and has a crack opening width of 0-13 cm, with a height difference between the two sides of the crack (rupture wall) of 0-0.2 m. The ground of the leading edge of the landslide was uplifted and cracked, with a maximum uplift height of approximately 1.7 m. The landslide shear outlet was clearly visible and exhibited well-developed scratches. The scratch direction was the same as the main slide direction of the underlying landslide. Landslide deformation severely cracked the building structure and obstructed the drainage channel. There was a loose residual soil layer on the surface of the slope of Landslide No.3, and many fractures and joints were present in the lower bedrock. During rainfall, rainwater penetrated the deep part of the slope along the rock layer surface, joints, and fractures, which greatly increased the bulk density of the rock and soil mass, and softened the argillaceous siltstones, which greatly decreased their shear strength. The excavation of the slope formed a steep surface, which reduced the load at the foot of the slope and thus reduced the anti-sliding force. During long-term seepage, the rock and soil mass near the landslide face was softened to form a weak zone mixed with joints and stratigraphic phases. During long periods of heavy rain, the weak zone became soaked, soft, and plastic, which reduced its shear strength. When downward force increased, the effective anti-sliding force of the weak zone was greatly reduced, resulting in a landslide. During this process, Landslide No.3 developed two slip surfaces. The maximum buried depths of slip surfaces 1 and 2 (corresponding to landslides 1 and 2) were 32 and 15.5 m, respectively, which means that landslide 2 overlaid landslide 1 and slip surface 1 creeping occurred before that of slip surface 2. The trailing edge of slip surface 1 developed a fissure, the characteristics of which are described above. As the fracture surface was not fresh, its' development time is unknown. As in the sliding process, landslide 2 first formed a continuous sliding surface, and its' sliding rate was slightly greater than that of landslide 1, landslide 2 was the first to cut out from the steep ridge of the landslide's front edge. As a result of the shearing action of landslide 2, landslide 1 developed multiple vertical cracks. Rainwater seeping down these cracks further lubricated slip surface 1, which resulted in drum mounds and cracks in the leading edge of the landslide. Slip surface 1 subsequently formed a continuous sliding surface, and Landslide No.3 entered the uniform deformation stage. Timely emergency measures prevented landslide deformation damage and halted landslide progression before entering the accelerated deformation stage. Considering its double-layer slip surface structure, a comprehensive combination of slope cutting, an anchor (cable), lattice beam, double-row prestressed anchor-pulling anti-slip pile, three-dimensional mesh grass greening, interception, drainage, and a hairy stone retaining wall was used to prevent and control the landslide. Long-term monitoring results showed that these methods had a high rectification effect and successfully controlled landslide deformation and displacement.
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