传统强度折减法通常对整个边坡区域进行折减，因而只能得到最小安全系数及对应的最危险临界滑动面。但在工程实践中，边坡的治理范围不能局限于最危险滑动面所包围的区域，不满足规范要求的次级滑动面范围内的坡体亦应得到治理。为了克服传统强度折减法在搜索次级滑动面方面的缺陷，提出了一种新的强度折减法。一般而言，边坡的屈服区域主要集中在滑动面两侧附近，形成一个沿滑动面分布的剪切破坏带，因此，在用强度折减法进行边坡稳定性分析时，只需对剪切破坏带范围内的局部坡体进行折减，则可得到该滑动面的安全系数和滑动面。基于以上认识，假设剪切破坏带沿对数螺旋曲线分布，不断调整对数螺旋曲线的形状以得到不同范围的剪切破坏带，对各种不同的剪切破坏带范围内的坡体进行局部折减计算，即可得到不同的安全系数及对应的滑动面。通过两个边坡算例（单台阶、双台阶）验证了该方法的可行性，并最后讨论了剪切破坏带的宽度对结果的影响。两个算例的计算结果表明，该方法不仅可以得到最危险临界滑动面，亦可得到任意安全系数对应的滑动面。

In the traditional strength reduction method, only the minimum safety factor and the critical slide surface can be acquired as its reduction region covers the whole slope model. However, in the slope engineering practice, we should treat the slope area not only surrounded by the global critical slide surface, but also located in the vicinity of the secondary slide surfaces. Thus, a modified strength reduction method is proposed to overcome the shortcomings of the traditional strength reduction method in searching the secondary slide surfaces. In general, the yield regions of slope are always distributed on both sides of a slide surface, which presents as a shear zone. Thus, a slide surface and its safety factor can be obtained by reducing the strength parameters of local slope area located within the shear zone. Based on the above understanding, it is supposed that the shear zones are distributed along the logarithmic spiral. Shear zones at different locations and ranges can be gained by changing the form of the logarithmic spirals, and then different secondary slide surfaces with their safety factors can be achieved through the strength reduction method. At last, the proposed method is verified through two case studies, and the effect of the shear zone breadth on calculated results is discussed. The results show that the proposed method can get not only the critical slip surface, but also different secondary slide surfaces corresponding to any safety factor.