Joint Rock Slope Stability Analysis Method And Application

Rock mass is defined as the collection of rocks which consists of joints,fissures, faults and so on, and its strength is mainly controlled by thediscontinuities or structural surfaces. The rock slopes are mainly composed ofrock masses and its instability or damage is always resulted in the damage ofdiscontinuities or structural surfaces. Therefore, the stability analysis of therock slopes should consider the cracks propagation of discontinuities such asjoints, fissures and faults.There have been some stability analysis methods of the rock slopesincluding the limited equilibrium method, the limited analysis method andother numerical methods so far. But the limited equilibrium method and thelimited analysis method have some difficulties in considering the crackspropagation, meanwhile the various numerical methods have somelimitations in simulating the cracks propagation, the FEM needs torecalculate the model mesh every time, and the numerical manifold methodmay exist local phenomenon at the crack tips, while the XFEM overcomesthe difficulties in high-precision meshing at the crack tips so that it is notnecessary to re-mesh during the crack propagation time.In this paper, the XFEM is applied for simulating the rock slope crackpropagation under the loadings, and according to the crack propagation, the vector method is carried out to analyze the stability of the rock slope againstsliding, at the same time, the strength reduction method is used for analyzingthe stability of collapse and falling. The specific studies and results are asfollows:(1) For the rock slopes which may collapse, the XFEM is forsimulating the deformation on the conditions of loading and the tensilestrength reduction simulating crack propagation whose sign is taken crackpropagation through the dangerous rocks as the damage of rock slopes andsafety factor is the reduction factor. Taking the Shuifu-Maliuwan Road as anexample, the paper calculated the safety factor at different locations andinclinations based on the maximum tensile stress to find out the mostdangerous locations in the tension cracks.(2) For the bedding rock slopes which have tension cracks. When thetension cracks do not penetrate the master, XFEM can find out the extendingpath of the tension cracks and the shape of the landslide. The vector methodis applied to calculating the total sliding force vector and the total drag forcevector of the landslide body which is composed of the drag force of thediscontinuities and the path the cracks extending along based on theconditions of the forces. Projecting the total sliding force vector and the totaldrag force vector of the landslide body to the sliding direction and getting theratio, we will get the safety factor. We also calculate the safety factors atdifferent lengths and locations of the tension cracks by the examples.(3) The internal cracks of the rock sloes may extend under thecondition of earthquakes which have bad effects on the stability of the slopes.This paper applies XFEM to simulating the propagation progress of theinternal cracks under the earthquakes, and judges the potential slipping surface according the conditions of crack propagation at any time, meanwhileuses the vector method to calculate the safety factor, finally, a safetyfactor-time curve can be drawn.(4) The limit equilibrium method regards the wedge as rigid body whenanalyzing the forces the wedge gets. Hoek-Bray method assumes the twoshear stresses at the bottom of the sliding surfaces parallel the intersect ofstructural surfaces. This paper solves the real forces of the wedge based onthe FEM and carries out vector method to calculate the safety factor againstsliding.(5) The XFEM can simulate the force of the rock slopes cut byanti-faceted structural surfaces, and the crack propagation of the rock pillarswhich may damage or fall by reduction of tension strength, which takes thereduction factor of tension strength that cannot keep stability as falling safetyfactor. For the rock pillars which cannot keep stability or have small safetyfactor under the forces, it is necessary to solve the forces it applies to theadjacent pillars after falling and continue analyzing the stability of adjacentpillars. Taking the Lianzi Cliff as an example, this paper carry out thestability analysis of the anti-overturning and anti-sliding of the pillars whichmay damage, eventually, it finds that the safety factor of anti-overturning is2.5and the afety factor of anti-sliding1.51, what is more, it proves thepossible failure modes is the whole sliding failure..