DEM Analysis Of The Stability Of Rock Slope And Its Application

Abstract:Particles flow code (PFC), a well-known discrete element method (DEM), has some unique characters and advances comparing to traditional continuum-type methods, particularly for the large-scale damage and non-linear behaviors. The study on rock slopes stability analysis using PFC, currently, is at a preliminary stage as procedures of creating models and theories of solving engineering problems are still premature. Furthermore, this method still takes calibration process for micro-parameters, formation of slope models, joints network models and so on into consideration, which are basically controversial. Based on unique advances of the particle descrete element method, PFC, the rock slopes stability is analysed. The PFC model for the section Zl in the Chenmenshan open pit mining slope is built, with which the application of this study is undertook. The summarized contents and conclusion are presented as follows.(1) Based on understanding of fundamental principle and calculation cycles, the general procedure for numerical analysis using PFC are studied in this dissertation. Uniaxial and biaxial compressive tests, direct shear tests, Brazil tests of disk and of flattened disk are conducted using PFC2D. The input micro-parameters are determined by these numerical tests, which is the so-called calibration process by the try-and-error.(2) Using a flattened disk in Brazil split tests can improve the stress states of loading faces. Series of Brazil tests with varied central angle of rock specimens are conducted with numerical models with the carful observation and analyses. Central angle of flats being20°is recommended to do the Brazil tests. Eventually, when the central angle of flats is20°, k (tensile strength corrective factor) is0.9315from the calculation results.(3) To study the effect of joint dip angle on the rock slope stability, eight sets of PFC models are made with various dip angles (i.e.,0°,15°,30°,40°,50°,60°,75°and90°) and the results show the dip angle of joint plays a vital role in the stability of the joint rock slope. When the dip angles of joint vary from30°to60°, the shearing slip on the dominated joint becomes a major factor to slope instability, while in other cases, the strength of rock matrix is of essence.(4) The method of combining the PFC model and concepts of limit equilibrium method is used to analyse slopes stability. The PFC slope model can automatically find the critical slip surface from calculation results at stage of incipient slope failure without any presumptions. The factor of safety can be further obtained by the LEM, Spencer method in this study, in which the slip surface is determined from the DEM model.(5) The PFC slope model for section Zl in the Chenmenshan open pit mining slope is built as well as the failure mode is studied. The result shows that the joint originating from the slope toe guides the formation of failure surface and the weak rock layer weakens the strength of rock matrix of the slope so that the critical slip surface tends to be deeper.The appropriate reinforcement measures to the slope are proposed based on the character of this slope. The slope toe should be boosted by anchorage cable, while the grouting reinforcement method should be adopted to improve the strength of weak layer. Finally, to further our understanding of probable landslide of this slope, the numerical study of this slope is conducted, by which the displacement and velocity from different parts of slope are traced and analysed.