Formation Mechanism and Stability Analysis of the Hejia Landslide

The existing research data show that, after reservoir impoundment, due to the repeated rise and fall of water level and water-rock interaction, the mechanical parameters of landslide are reduced, which will have an adverse effect on the stability of landslide. Therefore, sufficient attention must be paid to the stability of slope after reservoir impoundment. Hejia landslide is the largest landslide near the bank of Miaojiaba hydropower station, and its stability plays an important role in the normal operation of the hydropower station. Through field investigation and analysis of regional geological conditions, it is concluded that Hejia landslide is a large-scale landslide, through long-term sliding-bending deformation; it is generated from the external hard rock with thick layers and sliding zone for layered soft rock; the formation mechanism of landslide is as follows: (1) high-steep and hard-soft layered slope is the slope structure condition that caused the large landslide; (2) the existence of thick soft rock belt provides material conditions for the formation of slip surface; (3) certain air conditions provide displacement space for the separation and disintegration of the sliding body, and the landslide is stable at present. Numerical analysis results show that reservoir impoundment will adversely affect the stability of landslide. In order to ensure the normal operation of power station, certain engineering measures must be taken to treat Hejia landslide. After taking measures, years of monitoring data show that the deformation of Hejia landslide tends to be stable, and the current operation is normal, indicating that the engineering treatment measures are reasonable and feasible.

A Sensitivity Analysis of the Anisotropy of Hydraulic Conductivity to the Seepage, Deformation and Stability of Anti-dipping Layered Rock Slopes: A Case Study of the Pulang Area in Southwestern China

In this paper, in order to study the influence of anisotropy ratios and anisotropy directions on the seepage, deformations and stability of the anti-dipping layered rock slopes, Geo-studio software was used in this study for the numerical analysis of carbonaceous slate slopes on the unsaturated seepage, fluid–solid coupling, and stability theory in Pulang area. The results showed that the maximum surface water content of the layered rock slopes gradually decreased with increases of the water conductivity anisotropy ratio and decreases in the anisotropy angle of the anti-dipping layered rock slopes. In addition, the rainfall infiltration depths in the middle sections of the slopes were observed to be the most affected by the anisotropy ratio and dip angles of the rock formations. Meanwhile, the bottom sections of slopes were the least affected by the anisotropy ratio and the dip angles of the rock formations. In regard to the anti-dipping rock slopes, it was found that the anisotropy ratio and rock layer dip angles should be considered in the deformation and stability analyses. When the seepage of an anti-dipping layered slope was considered to be isotropic, the safety factors often were overestimated. As the anisotropy ratio decreases and the anti-dipping angles of the layered planes increases, the safety factors of the slopes will gradually decrease. This study provided a feasible scheme for evaluating the seepage, deformations and stability of the anti-dipping layered rock slopes in southwest China’s Pulang area.

DETERMINATION OF RATIONAL PARAMETERS OF SUPPORTING STRUCTURES MADE OF SOIL-CEMENT PILES ON LANDSLIDE-PRONE SLOPES

Purpose. The article proposes a method for determining the rational parameters of supporting structures made of soil-cement piles on landslide-prone slopes. Methodology. To achieve this purpose, the authors performed comparative calculations of finite-element models of landslide-prone layered slope with the arrangement of supporting structures of soil-cement piles: vertical, located at an angle to the vertical axis, combined with a concrete grillage, without grillage, with different diameters, with different distances between piles, but of the same length, which is justified by the location determined by preliminary calculations of the sliding surface. Findings. According to the results of calculating the contact problem of the interaction of the soil mass and the supporting structure, the regularities of formation of strength and stability of the reinforced landslide-prone slope were obtained, which makes it possible to predict its geomechanical stability depending on the possible location of the sliding surface curve. The method of increasing the stability coefficient of the soil slope depending on the variation of the parameters of the soil-cement supporting pile structure is substantiated. Numerical calculations substantiate the parameters of soil-cement pile supporting structures – the length of the piles, their diameter, the distance between the piles, the angle of their inclination and the feasibility of combining the piles with a concrete grillage. Originality. For the first time, the formation regularities of strength and stability of soil-cement supporting structure for strengthening the landslide-prone slopes are obtained, which makes it possible to predict their geomechanical stability depending on the possible location of the sliding surface curve. For the first time, the dependences of changes in absolute displacements, relative deformations, coefficients of strength, stability, as well as Mises stresses in the elements of supporting structures of soil-cement piles on the angle of their inclination, distance between piles and the presence of a concrete grillage that joins them. Methods for assessing and predicting the landslide danger of soil slopes were further developed, which allowed to substantiate the method of increasing the strength coefficient depending on the variation of the parameters of the soil-cement supporting structure. For the first time, the parameters of the method of increasing the stability of landslide-prone slopes with pile supporting structures based on the complex mathematical and centrifugal modeling using real landslides and similarity criteria are substantiated. Practical value. The authors have developed and patented a method of strengthening landslide slopes with the help of soil-cement piles, combined with a concrete grillage, located perpendicular to the movement vector of the landslide body.

A Sensitivity Analysis of the Anisotropy of Hydraulic Conductivity to the Seepage, Deformation and Stability of Anti-Dipping Layered Rock Slopes: A Case Study of the Pulang Area in Southwestern China

In this paper, in order to study the influencing effects of anisotropy ratios and anisotropy directions on the seepage, deformations and stability of the anti-dipping layered rock slopes, Geo-studio software was used in this study to carry out this test based on the unsaturated seepage, fluid-solid coupling, and stability theory numerical analysis of carbonaceous slate slopes in Pulang area. The results showed that the maximum surface water content of the layered rock slopes gradually decreased with increases of the water conductivity anisotropy ratio and decreases in the anisotropy angle of the anti-dipping layered rock slopes. In addition, the rainfall infiltration depths in the middle sections of the slopes were observed to be the most affected by the anisotropy ratio and dip angles of the rock formations. Meanwhile, the bottom sections of slopes were the least affected by the anisotropy ratio and the dip angles of the rock formations. In regard to the anti-dipping rock slopes, it was found that the anisotropy ratio and rock layer dip angles should be considered in the deformation and stability analyses. When the seepage of an anti-dipping layered slope was considered to be isotropic, the safety factors often were overestimated. As the anisotropy ratio decreases and the anti-tilt angles of the layered planes increases, the safety factors of the slopes will gradually decrease. This study provided a feasible scheme for evaluating the seepage, deformations and stability of the anti-dipping layered rock slopes in southwest China’s Pulang area.

Large deformation dynamic analysis of progressive failure in layered clayey slopes under seismic loading using the particle finite element method

This paper presents the failure analysis of layered clayey slopes with emphasis on the combined effect of the clay’s weakening behavior and the seismic loading using the particle finite element method (PFEM). Diverse failure mechanisms have been disclosed via the PFEM modelling when the strain-weakening behavior of clay is concerned. In contrast to a single layered slope exhibiting either a shallow or a deep failure mode, a layered slope may undergo both failure modes with a time interval in between. Seismic loadings also enlarge the scale of slope failure in clays with weakening behavior. The failure of a real layered slope (i.e. the 1988 Saint-Adelphe landslide, Canada) triggered by the Saguenay earthquake is also studied in this paper. The simulation results reveal that the choice of the strain-softening value controls the slip surface of the landslide and the amplification effect is important in the triggering of the landslide.

Stability Analysis of a Two-Layered Slope with Cracks by Finite Element Limit Analysis

In this study, to support slope stability estimating engineering, the stability of a slope with cracks lying on two-layered slopes was investigated by a self-developed adaptive element limit analysis (AFELA) code. Upper bound (UB) and lower bound (LB) results of soil additional gravity factor SF within 4% relative error were obtained to quantify the effects of several factors, including the Moore‒Cullen strength ratio, angle of the slope, thickness of the top layer, length of the crack, angle of the crack, and crack’s distance from the edge. Typical failure patterns were also discussed for deeper insight into the two-layered slope stability with cracks. In addition, the results of the AFELA code were compared with the actual situation of the slope and existing commercial calculation software to verify the reliability of this investigation.