An Analysis of Slope Stability Based on Finite Element Method and Distinct Element Method

The analysis of slope stability involves complex geological and topographical boundary conditions, nonlinear behavior of material stress-strain, coupling analysis of initial in-situ stress, water pressure and seismic load, etc., and in most cases, analytical solutions cannot be obtained. Under the background of the continuous development of computer and calculation method, the numerical analysis method represented by finite element has been gradually popularized and applied in geotechnical engineering in 1970s, and has developed into a powerful calculation and analysis tool. Among them, the finite element strength reduction method and the discrete element method are the two most widely used slope numerical analysis methods. In this paper, two typical cases, Ankang reservoir landslide and Wenma Highway slope, are simulated by the two methods. Taking Ankang reservoir landslide as the research object, this paper would use MIDAS / GTS finite element analysis software, and two-dimensional finite element numerical simulation would be carried out to study the influence of reservoir water level periodic fluctuation on the reinforcement effect of anti-slide pile. Under the condition of water saturation and water loss cycle, main material of landslide body and landslide belt, namely the strong weathered phyllite, displays obvious deterioration phenomenon, showing the trend of rapid decline first and then slow decline; after the anti-slide pile is set in the middle and front of the slope, the stability of it has been greatly improved, but with the increasement of the number of water level changes, the reinforcement effect of the anti-slide pile continues to weaken, and the weakening speed is fast at first, and then slows down. Taking the bedding slope of Wenma Highway as the research object, this pater would adopt UDEC discrete element software to simulate the deformation and failure process of the slope after excavated, and analysize the failure mechanism at the same time. The failure process of bedding slope can be divided into four stages: the formation of tension cracks caused by excavation, the expansion of cracks and the formation of deformation body, the sliding of deformation body and the accumulation of damaged rock mass at the foot of slope. Tensile failure is the main failure mode, and shear failure occurs locally. The failure of bedding slope starts from the foot of slope, which is traction sliding.

Sanxicun Landslide: An Investigation of Progressive Failure of a Gentle Bedding Slope

A gentle bedding slope (16° dip angle) failure at Sanxicun (SXC) village in Dujiangyan city was triggered by heavy rainfall in 2013. The landslide (composing of sandstone and mudstone strata) has a sliding distance of up to 1200 m and caused 166 deaths. After this failure event, a detailed field survey and a series of laboratory tests were carried out by us to investigate the progressive failure mechanism of the slope. The results revealed that the slope deformation could be traced back to the Ming Dynasty in China (400 years before) at least. A sliding block with a width of 330 m and a length of 240 m detached its original position, resulting in a depression belt with 10 m in width and 25 m in depth at the rear of the sliding block. On the scarp, a large number of cracks were widely observed not only in the sandstone but also in the mudstone. The field evidence revealed that the depression belt and cracked mudstone had provided convenience for water infiltration for a long time. The shake table test results showed that these cracks could be initiated and propagated in the slope during earthquakes. Especially, seismic stresses amplifications were induced in the mudstone to degrade this layer obviously. Besides, Direct shear tests of cracked mudstone with different immersion time were carried out. It was showed that the shear strength of mudstone decreased rapidly in the initial immersion and then tends to be stable gradually. Finally, numerical calculation indicated that the hydrostatic pressure in the depression belt and uplift pressure in the basal layer generated by the strongest rainwater in history (537.4 mm daily) caused the kilometer- slide of the block in 2013. We concluded that the catastrophic failure of the SXC landslide triggered by the rainwater in 2013 strongly depended on the pre- existing deformation and damage caused by historical earthquakes and rainwaters.

Shaking Table Test on Dynamic Response of Bedding Rock Slopes With Weak Structural Plane Under Earthquake

Taking a bedding rock slope with weak structural plane as the prototype, a shaking table test with a similarity ratio of 1:10 is designed and carried out. By analyzing the acceleration and displacement responses at different positions of the slope, the seismic response and instability mechanism of rock bedding slope under different seismic amplitudes, frequencies, and durations are studied. Before the failure of the slope, the rock bedding slope shows an obvious “elevation effect” and “surface effect” under the action of Wenchuan Wolong earthquake wave with different amplitudes. With the increase of the amplitude of the input seismic wave, the elevation effect and the surface effect gradually weaken. When the amplitude of the seismic wave reaches 0.9 g, the rock bedding slope begins to show damage, which demonstrates that the difference of PGA amplification coefficients on both sides of the weak structural plane increases significantly. Compared with the Kobe seismic wave and Wenchuan Wolong seismic wave, the excellent frequency of EL Centro seismic wave is closer to the first-order natural frequency of slope model and produces resonance phenomenon, which leads to the elevation effect of PGA amplification coefficient more significantly. Through the analysis of the instability process of rock bedding slope, it can be found that the failure mechanism of the slope can be divided into two stages: the formation of sliding shear plane and the overall instability of the slope.