Research On Applicability Of Shear Strength Reduction Method In Slope Stability Analysis

The stability analysis of slopes and landslides is a crucial problem in the geotechnical engineering field. Recently more and more scholars use numerical methods to analyze the stability of slopes. The shear strength reduction method is one of the methods scholars pay most attention to and it is also a commonly used method. However this method is under dispute and some further discussions are needed. It is introduced in this paper what has an impact on results. The density of grid and magnitude of the boundary are emphatically analyzed and a new understanding about boundary is brought forward. In addition, the applications of shear strength reduction method are elicited based on the analysis of ACADS examples, slope of ZhongShan power station, WanTang landslide and several slope examples. In the end, the MSSR technique is introduced and it makes finding potential sliding surface and corresponding safety factor possible. Therefore this paper will provide a dependable foundation for engineering design. The specific research achievements are as follows:1. Through the comparison of the criteria of slope failure of shear strength reduction, non-convergence of numerical solution is adopted as the criterion in this paper. It is emphatically analyzed that how much calculation parameters and boundary affect the results based on the analysis of ACADS examples. The results show that: elastic modules and poisson ratio have few influences on the factor of safety, and the influences can be ignored. The boundary has some effects on the results. With the augment of the boundary, the safety factor increases. The influences of right boundary and bottom boundary are larger than that of left boundary. As one of boundaries increases or decreases, the effect of other boundaries will become bigger or smaller. Therefore, when shear strength reduction method is applied to analyze the stability of slopes, the boundary should be appropriate and larger than range of the sliding surface at least.2. Bishop method is the same as shear strength reduction method in essence when used to deal with the stability of inhomogeneous slopes according to the analysis of Bishop method. Moreover, the shear strength reduction method is used to analyze common inhomogeneous slope of ACADS examples and the slope which contains the weak layer, and results are compared with that elicited by limit equilibrium method. At the same time, this method is applied to analyze stability of ZhongShan power station. The final results are satisfactory. It is proved that the shear strength reduction method can be applied to analyze the stability of inhomogeneous slopes.3. Based on the analysis of convex and concave slopes, the following results can be concluded: the shear strength reduction method can be adopted to analyze the stability of concave slopes; however when it is used to solve the stability of convex slopes, the real sliding surface will not be found out. According to the further analysis of convex slopes, that is, the influences of length and gradient of the second slope surface on results are presented. The conclusion is that as far as the convex slopes are concerned, if accurate sliding surface is not found out by shear strength reduction method, even though the length of the second slope surface becomes longer or shorter; the reasonable result is not gained by shear strength reduction method all the same. Thus, what affects the applicability of shear strength method is the gradient of the second slope surface. On the basis of above conclusion, the scope of application of shear strength reduction is elicited. Suppose the slope angle isθ, when the slope angle of the second slope surface is less thanθ/3 or more than3θ/4, the real sliding surface can be found out by shear strength reduction method. Otherwise the real sliding surface may be neglected. The analysis of examples validates dependability of the scope of application.4. MSSR technique is introduced for the first time, and this technique is the amelioration of shear strength method. MSSR technique can be used to find out the potential sliding surfaces and their corresponding factor of safety. However, the failure criterion is not introduced in the MSSR technique. Based on the analysis, it is elicited that plastic region and the contour shear strain increment together can be used to determine whether the slope is stable or unstable. In addition, some issues show up when MSSR technique is introduced. The problem is when the strength parameters are reduced; the model can not restore to the initial stable state. Otherwise, the stress and strain may have an effect on the results. Consequently, MSSR technique is meliorated in this paper. In addition, even though the convex slope is analyzed by MSSR method, it is possible that inaccurate sliding surface will be found out. At this time, the above application scope should be followed, that is, the relative gradient relationship between the first and the second slope surface. According to the analysis on the complex slope which is introduced by Y. M. Cheng, the above conclusions can be confirmed.5. On the basis of analysis methods of slope stability considering the stable seepage and earthquake respectively, it is elicited that the shear strength reduction method and limit equilibrium method are the same in essence. The conclusion provides the theoretical basis. Two slopes which consider the stable seepage and earthquake respectively are analyzed by different methods, and results show that the safety factor and position of sliding surface are approximately same. Therefore, it is proved that shear strength reduction method can be adapted to analyze the stability of slope considering above two situations.6. According to the analysis of residual thrust method, it is elicited that the residual thrust method and shear strength reduction method have the same processes when used to deal with the stability of landslide. It is the theoretical basis of stability analysis of landslide by shear strength reduction method. In the end, the WanTang landslide is analyzed by numerical simulation method, the position of sliding surface and corresponding safety factor are similar to that elicited by residual thrust method. The result validates that shear strength reduction method can be adapted to solve the stability of landslide. In addition, before analysis of the landslide, the sliding zone is known. Generally speaking, the strength parameters are smaller than that of sliding mass and much smaller than that of landslide bed. Therefore, the sliding surface which is found out by shear strength reduction method is always along the sliding zone.The main innovations are: 1. the bondage of boundary in the numerical simulation method is gotten rid of and a new understanding about boundary is put forward; 2. application scope of shear strength method is proposed when used to analyze the convex slopes; 3. the MSSR technique is introduced for the first time and is ameliorated.It is presented in this paper that the applicability of shear strength reduction method in slope stability analysis is analyzed relatively comprehensively on the basis of theoretical analysis and verification of ACADS examples and some specific engineering examples. This paper will provide theoretical foundation for the application of shear strength reduction method.