Numerical Simulation of Rainfall-induced Xianchi Reservoir Landslide in Yunyang, Chongqing, China 重试错误原因
YAN Jinkai ^(1){ }^{1}, MA Yan ^(1,**){ }^{1, *}, LIU Lei ^(2,^(**)){ }^{2,{ }^{*}}, WANG Zhihui ^(1){ }^{1} and REN Tianxiang ^(1){ }^{1}重试错误原因^(1){ }^{1} Chinese Academy of Geological Sciences, Beijing 100037, China重试错误原因^(2){ }^{2} Urban Construction School, Beijing City University, Beijing 100083, China重试错误原因
A calamitous landslide happened at 22:00 on September 1, 2014 in the Yunyang area of Chongqing City, southwest China, enforcing the evacuation of 508 people and damaging 23 buildings. The landslide volume comprised 1.44 million m^(3)\mathrm{m}^{3} of material in the source area and 0.4 million m^(3)\mathrm{m}^{3} of shoveled material. The debris flow runout extended 400 m vertically and 1600 m horizontally. The Xianchi reservoir landslide event has been investigated as follows: (1) samples collected from the main body of landslide were carried out using GCTS ring shear apparatus; (2) the parameters of shear and pore water pressure have been measured; and (3) the post-failure characteristics of landslide have been analyzed using the numerical simulation method. The excess pore-water pressure and erosion in the motion path are considered to be the key reasons for the long-runout motion and the scale-up of landslides, such as that at Xianchi, were caused by the heavy rainfall. The aim of this paper is to acquired numerical parameters and the basic resistance model, which is beneficial to improve simulation accuracy for hazard assessment for similar to potentially dangerous hillslopes in China and elsewhere.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 ( 0-24:000-24: 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^(@)59^(')34^(''E)108^{\circ} 59^{\prime} 34^{\prime \prime \mathrm{E}} and 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 m^(3)\mathrm{m}^{3} material in the source area and 0.4 million 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 0.142km^(2)0.142 \mathrm{~km}^{2} and corresponded to a Fahrböschung angle of 14^(@)14^{\circ}, based on the tangent of the ratio of fall height (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^(@)-12^(@)6^{\circ}-12^{\circ}. The main sliding direction of the landslide was deflected from 190^(@)190^{\circ} to 230^(@)230^{\circ} and then from 230^(@)230^{\circ} to 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 (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 2-38cm2-38 \mathrm{~cm}, generally 8-21cm8-21 \mathrm{~cm}, infill material in rock fissures is silty clay, plastic-rigid plastic, content 44%-46%44 \%-46 \%, and local boulders, block diameter 0.6-1.2m0.6-1.2 \mathrm{~m}. The thickness of the soil layer is in the range of 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.) (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%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^(@) < 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^(@) < 82^(@)210^{\circ}<82^{\circ}, an interval of 1-3m1-3 \mathrm{~m}, the extension of the fracture is about 2-4m2-4 \mathrm{~m}, crack openings of 0-0.2cm0-0.2 \mathrm{~cm}, and the crack surface is smooth; and (2) distinctive planes with attitudes of 312^(@) < 65^(@)312^{\circ}<65^{\circ}, an interval distance of 1-5m1-5 \mathrm{~m}, and cracks extend for 0.5-2m0.5-2 \mathrm{~m}.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%79 \% of total annual precipitation. According to local meteorological monitoring data, the heaviest rainfall occurred in the 24 h from 22:00 31^("st ")31^{\text {st }} August, 2014 to 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
2.3 Detailed information of Xianchi Reservoir landslide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 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^(@)190^{\circ} toward 230^(@)230^{\circ}, then further from 230^(@)230^{\circ} toward 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 0.142km^(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