Failure Analysis of Jointed Rock Slopes Based on a Modified Smooth-Joint Model
Date Issued
2015
Date
2015
Author(s)
Wu, Chun-Jung
Abstract
Rock slope often contains discontinuities such as joints, which is the key factor of rock slope stability. Conventionally, the limit equilibrium analysis and continuum numerical analysis are most used method for stability of jointed rock slope. However, the mechanical behavior of joint surface influence the sliding failure of rock block and massive transfer of block in jointed rock slope extremely. Therefore, the discrete element analysis which can consider the mechanical behavior of discrete block is an effective way to investigate the stability of jointed rock slope. In this study, PFC3D software is choose as the discrete element analysis tool, however, PFC is over-simplify in simulate joint surface behavior, thus it cannot react the mechanical behavior of roughness joint surface. Therefore, this study simulates the mechanical characteristic of joint surface through the improved method - Modified Smooth-Joint Model (MSJ model) which is developed by our research team. The MSJ model is based on Barton''s shear strength criterion, the mechanical behaviors are determined by various joint parameters. This study first verify out the accuracy of MSJ model by numerical direct shear tests, then we construct a simple rock slope model to discuss the relationships between limit equilibrium analysis and joint parameters, and then the influence of joint continuity is investigated, finally discuss about the application of the MSJ model on rock slope failure analysis. In the part of MSJ model verification, we first to examine the reliability of intact rock micro-parameters through the simulation data of uniaxial compress test; then the rationality of joint parameters are verified by the results of direct shear test; finally, the simulation results of direct shear test and Barton''s shear strength model are compared to ensure that they are equal, and the SJ model is treated as the control group. The comparison shows MSJ model can reasonably represent the trend of Barton''s model which shows friction angle is correlate with normal stress, while SJ model cannot point out this important characteristic in roughness joint. In the section of simple rock slope analysis, trapezoid slope with single joint is used in the simulation. The first step is changing the joint friction angle parameters to analyze the relationship between the joint friction angle and dip angle according to the limit equilibrium theory; second, the revised MSJ model is used to investigate the spatial distribution of friction angle to recognize the influence of normal stress acted on joint surface; finally, the continuous joints are alter to discontinuous joints to simulate the effect of rock bridge, and then sequentially investigate the influence of joint persistence, intact rock strength and rock bridge type to the rock slope stability through failure analysis of rock slope. According to the simulation results of simple rock slope, there are some conclusions and suggestions of the MSJ model. The simulation results show that even joint friction angle is lower to dip angle, the slope is not necessarily to slip in numerical rock slope. We suggest that three-dimensional limit equilibrium analysis can be adapted in future to correct the settings of numerical model; joint friction angles is vary with the distribution of upper block weight, this feature shows the mechanical behavior of roughness joint is influence by normal stress; if joint surface is discontinuous, the crack distribution are correlate to the length and type of rock bridges, and the failure of rock bridge will cause upper block to slide. We recommended that MSJ model can be used to simulate real rock slope in the future, and exploring the complex mechanism of jointed rock slope failure to evaluate the analysis and design of geo-engineering.
Subjects
jointed rock slope
discrete element analysis
MSJ model
Type
thesis
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