A study of residual strength and method for evaluating the stability of slopes

在滑坡稳定性评价中，弄清滑动面上材料的剩余强度特征是十分重要的。剩余强度是粘土颗粒最终定向的表面上的最小剪切强度。达到残馀状态所需的最小剪切位移的大小取决于粘土颗粒的性质和法向有效应力。泥岩的位移量要求达到40-60 cm，砾石凝灰质土的位移量要求达到200-300 cm。环剪试验是获得滑坡土残馀状态的有效方法，但由于滑坡土的大位移剪切和排水条件需要较长的时间，残馀强度参数与滑坡土的物理和矿物学特性密切相关。结果表明，粘粒含量、塑性指数和蒙脱石含量是估算剩余强度参数的有效指标，而…反分析的强度参数不能预测易发生滑坡的斜坡的稳定性。该方法结合了反分析、剩余强度参数和峰值强度参数、剩余系数、安全系数和摩尔-库仑方程，可以进行大范围的稳定性评价。强度参数的计算方法具有以下特点：(1)将室内强度参数纳入土的力学有效性评价。(2)介绍了安全系数反分析中的标准条分法。(3)引入残差因子后，在表达式中加入了剩余强度和峰值强度两个参数。(4)考虑了滑坡体的类型和滑动面的情况，通过估计残差系数计算安全系数，可以有效地确定处于休眠状态的易发生滑坡的斜坡的安全系数，特别是在许多滑坡块正在展布的地区，其中一些斜坡实际上正在发生滑坡。较少

In evaluating the stability of landslide, it is important to clarify the characteristics of residual strength of materials in the slip surface zone. The residual strength is the minimal shear strength along the surface where clay particles are finally oriented. The magnitude of the minimal shear displacement that is needed to attain to the residual state depends on the clay particle property and the normal effective stress. The magnitude of displacement as long as 40-60 cm for mudstone and 200-300cm for gravelly tuffaceous soil were required. A ring shear test is an effective method to attain the residual state, although long time is required due to the large-displacement shearing and the drained conditions.Residual strength parameter is closely connected with the physical and mineralogical characteristics in landslide soils. It is concluded that clay fraction, plastisity index and amount of smectite appear to be a useful guide to estimate the residual strength parameter, and that furt … More her examination of the matter is warranted.Back-analyzed strength parameters were not capable of predicting stability of landslide-prone slopes. The proposed method that incorporates a combination of back-analysis, residual and peak strength parameters, residual factor, safety factor and the Mohr-Coulomb's equation makes it possible to conduct a large scale stability evaluation.The method for calculations of strength parameters are featured by the followings: (1) Laboratory strength parameters are incorporated into the evaluation for soil mechanical validity. (2) The standard slice method, a method used in back-analysis for safety factors, is introduced. (3) Two parameters of residual and peak strengths are incorporated into the expression after residual factors are introduced. (4)The type of slides and the condition of slip surfaces are taken into considerations.Calculations of safety factors through the estimated residual factor are believed to be effective in determining safety factors of those landslide-prone slopes in dormant state, particularly of those found in areas where many landslide blocks are being spread out, some of which are actually undergoing slides. Less