| dc.description.abstract | The properties of rock mass such as mechanical behavior and hydraulic conductivity are controlled by the direction because of the orientation of discontinuities. In the stability analyses of the dip slope and the anti-dip slope, the limit equilibrium method and two-dimensional numerical methods ignoring the end effect of the slope strike boundary are often used. However, the stability analyses of oblique slope are three-dimensional problems. The boundary condition of the slope strike plays an important role of the collapse behavior of the rock slope.
PFC3D is adopted in this study to generate BPM and DFN to be a synthetic rock slope model with a set of discontinuity. Resreach the collapse behavior of rock slope with different |α_j-α_s | by using different boundary conditions. This study takes a 3D slope model with slope height 50 meters, slope angle 60°, and slope length 200 meters as an example. The boundary conditions used include fixed, periodic, roller, and free, and different |α_j-α_s | are 0˚、10˚、15˚、20˚. Based on the results of numerical simulation, we can discuss the collapse process of rock slopes in different variables, and describe the collapse behavior of rock slope by using quantitative indicators such as the impact area, the direction of displacement, and the energy release of landslide. Base on the results, introduce how to reduce the end effect, determine the critical oblique angle, and summarize the applicable scenarios of each boundary condition.
Numerical analysis results show that：(1) PFC3D can reasonably simulate the collapse behavior of rock slopes at different |α_j-α_s |. There will be several macroscopic failure surfaces in the process. The progressive failure happens with the initial failure surface generating near the top of the slope, and the depth of the failure surface is relatively shallow. The subsequent failure surface gradually retrogresses from the top of the slope, and the failure surface is deeper. (2) The synthetic rock slope model is composed of particles of different radius. When dealing with the data of the particle displacement vector, this study proposes the weighted displacement method in order to reasonably reflect the influence of the size of particles. The displacement vector of each particle is multiplied by the weight of the particle and divided by the sum weight of particles. The weighted displacement method can effectively reduce the influence of trivial displacement and tiny particles, and can more reasonably present the overall displacement of rock slopes. Based on the weighted displacement method, this study discusses the horizontal displacement direction of the collapsed body in at different |α_j-α_s |. The results show that the horizontal displacement direction of the collapsed body in each boundary condition is between α_s and α_j, and is relatively consistent with α_s. Besides, the energy release of landslide is sum of the vertical displacement multiplied by the weight of the particles. (3) In this study, the rock slope model at different |α_j-α_s | and in each boundary condition is segmented to left, middle, right, and the length ratio is 1:2:1. The serults show that the collapse behavior such as direction ofdisplacement, energy release of landslide, and collapse volume are quite close to those of periodic boundary condition. It can be confirmed that the influence of end effect can be reduced by removing the left and right segments. In addition, periodic boundary conditions are effected by the minimal end effect, and are the most suitable boundary conditions to research the collapse behavior of rock slope at different oblique angles. (4) As |α_j-α_s | increases, the collapse volume and the energy release of landslide are also decreases sharply.In this study, |α_j-α_s | corresponding to when the rock slope tends to be stable (or only thimbleful collapse volume) is called critical oblique angle. Taking a rock slope in periodic boundary as an example, the critical oblique angle is 20°, which is consistent with general engineering experience or technical regulations. (5) Periodic boundary conditions can effectively reduce the end effect, the number of particles and the calculate time, and provide a method suitable for simulating the behavior of infinite slopes. When the slope length ratio L/H>6, it can be regarded as an infinite slope, but the number of particles will be too many, resulting in a long calculation time. It is recommended to use periodic boundary conditions to periodically extend the model to improve computing efficiency. When the slope length ratio L/H≦6, it can be regarded as a finite slope. According to the site, the side surface of the rock slope is completely unsupported, with a retaining wall and a rough wall, and with a retaining wall and a wall. The situation with a smooth surface corresponds to three boundary conditions: free, fixed, and roller. | en_US |