基于局部软化阶梯双折减法的土坡稳定性研究

Research on Progressive Failure of Slope based on Softening Law and Step Double Reduction Method

强度折减法是边坡稳定性分析中广泛使用的数值计算方法,传统整体强度折减法对黏聚力和内摩擦角采用同一系数进行折减。由于两强度参数发挥作用先后以及衰减程度的不同,传统整体强度折减法不能真实的反映土体渐进破坏过程,一些学者提出运用双折减法来探究边坡的破坏问题。基于土体应变软化特性,通过土体的峰值与残余强度建立起黏聚力和内摩擦角之间的关系,将得到的强度参数关系式作为双参数折减组合的依据。该方法以破坏接近度作为判别土体是否破坏的标准,引入局部阶梯折减的思想,对局部破损区域(FAI>0.8)采用不同的折减组合,研究均质土坡的渐进破坏过程。计算结果表明,局部软化阶梯双折减法可以体现两强度参数发挥作用的先后顺序,整理出两参数间的关系式为一次函数,自变量对应的参数先发挥,因变量对应的参数后发挥;在算例中,黏聚力的折减系数大于内摩擦角的折减系数,黏聚力的强度储备比内摩擦角大,发挥得较为充分;模拟计算出的破损区面积以及边界处的塑性应变差值更加连续、平稳;阶梯双折减方法得到的综合安全系数小于整体折减法的安全系数,在工程应用上偏于安全,与其他学者得出的结论一致;受网格密度的影响,综合安全系数的范围为1.207~1.229,该范围可为工程设计和施工提供参考。

The strength reduction method is a widely used numerical calculation method in slope stability analysis. The traditional strength reduction method uses the same reduction coefficient for cohesion and internal friction angle. Because the two strength parameters play different roles in deformation sequence and have different attenuation degrees,the traditional strength reduction method cannot truly reflect the progressive failure process of the soil. Some scholars proposed using the double reduction method to explore the failure of the slope. Based on the strain softening characteristics of soil,the relationship between the cohesion and the internal friction angle was established through the peak value and residual strength of the soil. The proposed strength parameter relationship was then used as the basis for the double parameters reduction combination. The failure approach index was chosen as the criterion to determine whether the soil is damaged,the idea of local step reduction was introduced,and different reduction combinations were used for the local yield area(FAI>0.8)to study the progressive failure process of homogeneous soil slope. The calculation results show that the local softening step double reduction method can reflect the action sequence of the two strength parameters. The relationship between the two parameters is sorted out as a linear function,in which the parameter corresponding to the independent variable works first,and the parameter corresponding to the dependent variable works later. In the calculation example of this paper,the reduction coefficient of the cohesion is greater than that of the internal friction angle,and the strength reservation of the cohesion is larger than that of the internal friction angle,so the cohesion is fully utilized. The calculated damaged area and the plastic strain difference at the boundary are more continuous and stable. The comprehensive safety factor obtained by the step double reduction method is smaller than that of the overall reduction method,which is safer in engineering applications and is consistent with the conclusions obtained by other scholars. Affected by the density of the mesh,the safety factor ranges from 1.207 to 1.229,which can provide reference for engineering design and construction.