Numerical Simulation of Rainfall-induced Xianchi Reservoir Landslide in Yunyang, Chongqing, China 重试    错误原因

Key words: geohazards, landslide, post-failure, rapid and long runout, ring shear test 重试    错误原因
Citation: Yan et al., 2024. Numerical Simulation of Rainfall-induced Xianchi Reservoir Landslide in Yunyang, Chongqing, China. Acta Geologica Sinica (English Edition), 98(2): 505-517. DOI: 10.1111/1755-6724.15146 重试    错误原因

Rapid and long-runout landslides caused by heavy rainfall occur frequently in southwest China (Xu et al., 2010; Dai et al., 2011; Huang et al., 2011; Yin et al., 2011, 2016; Wu et al., 2012; Yin and Xing, 2012; Guo et al., 2019). These hazardous landslides caused a series of casualties and property damage (Tang et al., 2009; Huang et al., 2012; Zhang et al., 2014; Yin et al., 2015; Wu et al., 2023). In southwest China, the landslides characteristics have been determined as follows: (1) pore-water pressure increases rapidly and the landslide occurs suddenly; (2) the event has the characteristics of impact scraping in the post-failure process; (3) the disaster chain of rapid and long-runout formed easily. 重试    错误原因

Numerical simulation is an important method for analyzing landslide movement. Inverse analysis should be carried out to restore post-failure behavior and assess the risk of landslide movement (Lin et al., 2016; Xing et al., 2017; Ouyang et al., 2018), which also will improve the accuracy of predicting rapid and long-runout landslides. The SPH (Smoothed Particle Hydrodynamics) method, based on the hypothesis of continuous medium and threedimensional (3D) generalization, has unique advantages in dealing with large deformation, free interfaces, and deformation boundaries, and can efficiently compute the destructive motion process after landslides (Hungr and McDougall, 2009; Xing et al., 2014; Gao et al., 2017, 2020). This application of approach should be based on 重试    错误原因
sufficient understanding of the landslide motion processes, such as shoveling and liquefaction effects, based on a hybrid model and drag effects based on a two-fluid model (Sassa et al., 2010; Pudasaini, 2012; Pastor et al., 2015, 2021; Gao et al., 2017, 2022, 2023). In addition, the selection of model parameters is very important. The parameters employed in previous studies utilized empirical value, which is based on the analysis of post-landslide damage process by the trial-and-error method. In order to improve the generalization of numerical calculation applications, the determination of parameters based on physico-mechanical tests is particularly important, especially for the consideration of pore-water pressure Landslides triggered by rainfall are caused by the rise of pore-water pressure into the ground (Wilson, 1995; Wieczorek, 1996; Wang et al., 2003, 2014). In order to study the residual shear resistance and pore-water pressure along the sliding surface of a landslide under large shear displacements, the ring shear device was designed as a means of determining the simulation parameters (Sassa, 1988; Sassa et al., 2004). 重试    错误原因

From August 31st to September 2nd, 2014, the northeast area of Chongqing suffered torrential rainstorms. The maximum daily rainfall in the rainfall center area (Xianchi precipitation station) was 368.3 mm ( $0-24:00$$0-24:00$0-24:000-24: 00 on September 1st). Heavy rainfall was apparently the inducing factor in the disaster chain of the Xianchi Reservoir landslide-debris flow (Li et al., 2022; Gao et al., 2023b, c). 重试    错误原因

In this paper, we aim to investigate and record the postfailure motion process of the Xianchi reservoir landslide was in detail. To accurately determine the numerical calculation parameters, samples from the sliding main body were submitted to a GCTS ring shear apparatus to determine the parameters of shear and pore-water pressure. The mobility of Xianchi reservoir landslide is analyzed by using the numerical simulation method. The purpose of this study is to combine test parameters and simulation models with the aim of improving the accuracy of hazard assessment in the Chongqing and similar regions. 重试    错误原因

A devastating landslide happened at 22:00 on September 1, 2014, at ${108}^{\circ }{59}^{\prime }{34}^{\prime \prime \mathrm{E}}$${108}^{\circ }{59}^{\prime }{34}^{\prime \prime \mathrm{E}}$108^(@)59^(')34^(''E)108^{\circ} 59^{\prime} 34^{\prime \prime \mathrm{E}} and ${31}^{\circ }{16}^{\prime }{23}^{\prime \prime }\mathrm{N}$${31}^{\circ }{16}^{\prime }{23}^{\prime \prime }\mathrm{N}$31^(@)16^(')23^('')N31^{\circ} 16^{\prime} 23^{\prime \prime} \mathrm{N} in Yunyang Country, Chongqing City, southwest China, which caused 508 people evacuation and 23 damaged buildings (Fig. 1). The landslide volume was composed of some 1.44 million ${\mathrm{m}}^3$${\mathrm{m}}^3$m^(3)\mathrm{m}^{3} material in the source area and 0.4 million ${\mathrm{m}}^3$${\mathrm{m}}^3$m^(3)\mathrm{m}^{3} shoveled material. The runout of the debris flow extended 400 m vertically and 1600 m horizontally, which spanned an area of $0.142{\mathrm{km}}^2$$0.142{\mathrm{km}}^2$0.142km^(2)0.142 \mathrm{~km}^{2} and corresponded to a Fahrböschung angle of ${14}^{\circ }$${14}^{\circ }$14^(@)14^{\circ}, based on the tangent of the ratio of fall height $(\mathrm{H})$$(\mathrm{H})$(H)(\mathrm{H}) to horizontal runout distance ( L ) between the crest of the source zone and toe of the deposit (Heim, 1932; Fig. 1). 重试    错误原因
Yunyang County is located in the upper region of the Yangtze River, which is an important hub of the ecological economic zone of the Three Gorges Reservoir area. It is also one of the areas with a high incidence of landslide hazards. It is therefore very important to study the postfailure and risk assessment of landslide disasters in this area and to improve the technology of disaster prevention and mitigation in this area (Gao et al., 2022; Li et al., 2022). 重试    错误原因

The topography of the research area is mountainous and hilly, forming a basin shape surrounded by mountains on 重试    错误原因
all sides. The elevation ranges from 750 m to 1374 m . The Xianchi reservoir is situated in the foothills area, and is one of the three largest reservoirs in Yunyang County. The orientation of the mountains is northeast-southwest; the slope gradient is $6^{\circ }-{12}^{\circ }$$6^{\circ }-{12}^{\circ }$6^(@)-12^(@)6^{\circ}-12^{\circ}. The main sliding direction of the landslide was deflected from ${190}^{\circ }$${190}^{\circ }$190^(@)190^{\circ} to ${230}^{\circ }$${230}^{\circ }$230^(@)230^{\circ} and then from ${230}^{\circ }$${230}^{\circ }$230^(@)230^{\circ} to ${180}^{\circ }$${180}^{\circ }$180^(@)180^{\circ} (Fig. 2). 重试    错误原因

According to our field survey, the strata lithology of the landslide can be divided mainly into two parts: (1) the overlying Quaternary residual and alluvial deposits $\left({\mathrm{Q}}_4{}^{\text{el}+\mathrm{de}}\right)$$\left({\mathrm{Q}}_4{}^{\text{el }+\mathrm{de}}\right)$(Q_(4)^("el "+de))\left(\mathrm{Q}_{4}{ }^{\text {el }+\mathrm{de}}\right), containing crushed stone, silty clay, and gravel soil. The composition of the crushed stone is sandstone and mudstone, angular, subangular, particle size $2-38\mathrm{cm}$$2-38\mathrm{cm}$2-38cm2-38 \mathrm{~cm}, generally $8-21\mathrm{cm}$$8-21\mathrm{cm}$8-21cm8-21 \mathrm{~cm}, infill material in rock fissures is silty clay, plastic-rigid plastic, content $44\mathrm{\%}-46\mathrm{\%}$$44\mathrm{\%}-46\mathrm{\%}$44%-46%44 \%-46 \%, and local boulders, block diameter $0.6-1.2\mathrm{m}$$0.6-1.2\mathrm{m}$0.6-1.2m0.6-1.2 \mathrm{~m}. The thickness of the soil layer is in the range of $5-9\mathrm{m}$$5-9\mathrm{m}$5-9m5-9 \mathrm{~m}, and the crushed stone was the main material of the main sliding body; and (2) the underlying Jurassic Upper Shaximiao Formation (Fm.) $\left({\mathrm{J}}_{2}S\right)$$\left({\mathrm{J}}_{2}S\right)$(J_(2)S)\left(\mathrm{J}_{2} S\right), which is quartz-siltstone and is mainly a strongly weathered sandstone characterized by chip-like and thicklayered structure, and particle mineral components mainly of quartz and feldspar. Joint fissures are developed in the rock mass, and the core is mostly broken. The rock mass is coarse, and the rock core takes up to $68\mathrm{\%}$$68\mathrm{\%}$68%68 \%. The strata are composed of a thin layer of mudstone, an off-white sandstone and clastics. The particle mineral components are mainly quartz, feldspar, and a locally sandwiched thinlayer of mudstone. 重试    错误原因

The research area is on the east wing of the Macao river upper bend (Fig. 2), the bedrock is the Jurassic Upper Shaximiao Group, and the attitude of the bed is ${172}^{\circ }<{22}^{\circ }$${172}^{\circ }<{22}^{\circ }$172^(@) < 22^(@)172^{\circ}<22^{\circ}. There are no tectonic faults in the landslide area, whereas two fissure groups are developed as: (1) distinctive planes with attitudes of ${210}^{\circ }<{82}^{\circ }$${210}^{\circ }<{82}^{\circ }$210^(@) < 82^(@)210^{\circ}<82^{\circ}, an interval of $1-3\mathrm{m}$$1-3\mathrm{m}$1-3m1-3 \mathrm{~m}, the extension of the fracture is about $2-4\mathrm{m}$$2-4\mathrm{m}$2-4m2-4 \mathrm{~m}, crack openings of $0-0.2\mathrm{cm}$$0-0.2\mathrm{cm}$0-0.2cm0-0.2 \mathrm{~cm}, and the crack surface is smooth; and (2) distinctive planes with attitudes of ${312}^{\circ }<{65}^{\circ }$${312}^{\circ }<{65}^{\circ }$312^(@) < 65^(@)312^{\circ}<65^{\circ}, an interval distance of $1-5\mathrm{m}$$1-5\mathrm{m}$1-5m1-5 \mathrm{~m}, and cracks extend for $0.5-2\mathrm{m}$$0.5-2\mathrm{m}$0.5-2m0.5-2 \mathrm{~m}. 重试    错误原因

Fig. 1. Geographical location and geomorphology images of the rockslide-debris flow at Xianchi reservoir. 重试    错误原因
(a) Xianchi reservoir landslide geographical location in Yunyang, Chongqing, China; (b) pre-slip image; © post-slip image. 重试    错误原因

Fig. 2. Detailed topography of the Xianchi reservoir landslide. 重试    错误原因

The study area is located in the Sichuan Basin. The climate is characterized by a subtropical humid monsoon climate with abundant precipitation. The topography of Yunyang County is complicated, with great differences in height, and variable temperature with altitude, showing distinct stereoscopic climatic characteristics. The annual precipitation ranged from 1752.6 mm in 1963 to 785.8 mm in 1966 with a multi-year average annual precipitation of 1154.1 mm . The amount of precipitation in the rainy season accounts for $79\mathrm{\%}$$79\mathrm{\%}$79%79 \% of total annual precipitation. According to local meteorological monitoring data, the heaviest rainfall occurred in the 24 h from 22:00 ${31}^{\text{st}}$${31}^{\text{st }}$31^("st ")31^{\text {st }} August, 2014 to $1^{\text{st}}$$1^{\text{st }}$1^("st ")1^{\text {st }}, September, 2014 with a cumulative total of 368.3 mm (Fig. 3a). The regional rainstorm affecting the reservoir area was characterized by shorttime and high-strength with a cumulative rainfall over two days of 417.9 mm before the landslide happened (Fig. 3b), which is the largest historical rainfall record of the Xianchi reservoir. The heavy rainfall was the important 重试    错误原因
inducing factor for the landslide-debris flow disaster chain in the Xianchi reservoir. 重试    错误原因

The Xianchi reservoir landslide, characterized by a rapid and long-runout landslide, developed into a debris flow under the influence of heavy rainfall. The sliding mass is approximately 1.44 million ${\mathrm{m}}^3$${\mathrm{m}}^3$m^(3)\mathrm{m}^{3}, and the main component of the sliding body was gravel. The main body moved fluidly in a direction of ${190}^{\circ }$${190}^{\circ }$190^(@)190^{\circ} toward ${230}^{\circ }$${230}^{\circ }$230^(@)230^{\circ}, then further from ${230}^{\circ }$${230}^{\circ }$230^(@)230^{\circ} toward ${180}^{\circ }$${180}^{\circ }$180^(@)180^{\circ} into the reservoir. The back margin of the landslide is at a height of 1250 m , while the front boundary of the accumulation area is at an elevation of 850 m (Fig. 4a). 重试    错误原因

The landslide maximum width is 280 m and the axis length from the leading edge to the trailing edge is about 1600 m . The total area of the landslide is about $0.142{\mathrm{km}}^2$$0.142{\mathrm{km}}^2$0.142km^(2)0.142 \mathrm{~km}^{2}. The maximum thickness of the landslide is about 28 m with an average thickness of 10 m . The landslide damaged 23 buildings on the north bank of the reservoir. Based on 重试    错误原因