# Formation and Failure Mechanism of the Xinfangzi Landslide in Chongqing City (China)
###### Abstract  
At 2:00 a.m. on 1 July 2020, after several days of continuous heavy rainfall, the Xinfangzi landslide occurred in Zhengping Village, Ganshui Town, Qijiang District, Chongqing City, China. The area of the landslide was about \(3.85\times 10^{4}\) m\({}^{2}\) and the volume was about \(71.22\times 10^{4}\) m\({}^{3}\). The Xinfangzi landslide can be defined as a push-type landslide. Specifically, the main sliding area pushed the front squeezing area, causing it to slide laterally. The entire slip path of the landslide was a broken line, while the right edge and the front shear outlet position slipped loosely in a circular arc. In this study, finite element numerical calculations were used to compare and analyze the multisection plastic deformation of the landslide under natural and rainfall conditions based on field investigations. The formation and failure characteristics of the Xinfangzi landslide were further revealed. The results show that the cross and longitudinal sections of the landslide were in a critical state of instability under natural and rainfall conditions. A compound section was established along the slip path based on the cross and longitudinal sections. Due to the extrusion of the trailing edge of the landslide, the compound section's leading edge was in a state of instability under natural conditions. Under rainfall conditions, the increase in the unit weight of the sliding mass was superimposed on the compound section, which amplified the thrust of the trailing edge and further accelerated the overall sliding process of the landslide. Based on the macroscopic deformation of the landslide, it was found that the sliding of the trailing edge of the landslide is the key factor promoting the failure of the front edge, and local slump is possible under rainfall conditions.  
rainfall induced landslide; numerical simulations; factor of safety; formation and failure characteristics; catastrophic mechanism +
Footnote †: journal: Applied Sciences  
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the mechanical state of landslides effectively [7; 8; 9]. Based on the principle of similarity and field survey results, physical model experiments are also used to predict or reproduce the evolution of landslides [10; 11; 12].  
The numerical simulation can obtain the stress or strain distribution and analyze the dynamic failure. When performing numerical calculations, the finite element method (FEM) [13; 14; 15; 16; 17], discrete element method (DEM) [18; 19], material point method (MPM) [20; 21; 22], and the smoothed particle method (SPM) [23] are commonly used. Notably, it is important to determine the geological model, mechanical model, and mechanical parameters during the numerical simulation. In addition, these settings are the key factors to ensure the simulation results' reliability and validity [24; 25]. Since there are many factors affecting the stability of landslide, mathematical methods are adapted to determine the stability quantitatively or semi-quantitatively, such as dissipation theory [26; 27], chaos theory [28], stochastic theory [29], fuzzy theory [30], gray system theory [31], catastrophe theory [32], and so on. Furthermore, combining field investigations and numerical simulations is still an effective and fast method of analyzing the evolution process of a landslide, and it can be promoted in the actual application process.  
At around 2:00 a.m. on 1 July 2020, after several days of continuous heavy rainfall, the Xinfangzi landslide (\(106^{\circ}44^{\prime}59.88^{\prime\prime}\) E, \(28^{\circ}43^{\prime}13.50^{\prime\prime}\) N; Figure 1) occurred in Zhengping Village, Ganshui Town, Qijiang District, Chongqing City, China. Based on on-site investigations, FEM was used to analyze the formation and failure characteristics of the Xinfangzi landslide and the related inducing factors. The plastic deformation of multiple sections under natural and rainfall conditions were compared to further reveal the catastrophic mechanism of the Xinfangzi landslide.