Limit equilibrium method(LEM) of slope stability and calculation of comprehensive factor of safety with double strength-reduction technique

When the slope is in critical limit equilibrium(LE) state, the strength parameters have different contribution to each other on maintaining slope stability. That is to say that the strength parameters are not simultaneously reduced. Hence, the LE stress method is established to analyze the slope stability by employing the double strengthreduction(DSR) technique in this work. For calculation model of slope stability under the DSR technique, the general nonlinear Mohr–Coulomb(M–C) criterion is used to describe the shear failure of slope. Meanwhile, the average and polar diameter methods via the DSR technique are both adopted to calculate the comprehensive factor of safety(FOS) of slope. To extend the application of the polar diameter method, the original method is improved in the proposed method. After comparison and analysis on some slope examples, the proposed method's feasibility is verified. Thereafter, the stability charts of slope suitable for engineering application are drawn. Moreover, the studies show that:(1) the average method yields similar results as that of the polardiameter method;(2) compared with the traditional uniform strength-reduction(USR) technique, the slope stability obtained using the DSR techniquetends to be more unsafe; and(3) for a slope in the critical LE state, the strength parameter φ, i.e., internal friction angle, has greater contribution on the slope stability than the strength parameters c, i.e., cohesion.

THREE-DIMENSIONAL SLOPE STABILITY ANALYSIS BASED ON NONLINEAR FAILURE ENVELOPE

The effects of nonlinearity of strength envelopes on 3D slope stability analysis are investigated.A power relation for the nonlinear envelope is employed to derive the 3D factor of safety equations of an extended Spencer method hich satisfies boty force equilibrium and moment equilibrium.Then,a search procedure is presented based on dynamic programming to determine the 3D critical slip surface for a general slope,Linear and nonlinear strength envelopes used for slope stability computations are obtained by fitting curves to the 103 strength data of consolidated-undrained(CU)triaxial compression tests for compacted Israeli clay.Results of a typical 3D problem show that a linear approximation of the nonlinear strength envelope may lead to a significant overestimation of calculated safety factors.

冻结砂土的应力-应变关系及非线性莫尔强度准则

对于-6℃的冻结砂土进行一系列的试验,结果表明,当围压小于3.0MPa时,其应力–应变关系具有明显的应变软化现象;当围压大于3.0MPa时,其应力–应变关系则具有明显的应变硬化现象。针对广义的双曲线模型并不能很好地描述-6℃冻结砂土在围压大于3.0MPa时的应力–应变关系,邓肯–张模型也不能理想地反映围压小于3.0MPa时-6℃冻结砂土的应变软化特性,提出既能描述应变软化现象又能描述应变硬化现象的改进的邓肯–张模型。研究表明,其结果和试验结果吻合良好。由于压融现象的存在,当围压大于一定值后,冻结砂土的剪切强度随围压的增大而减小。如果用莫尔–库仑准则来描述冻结砂土的剪切强度,会产生较大的误差。为解决这一问题,提出非线性莫尔强度准则。研究结果表明,其精度较高,比莫尔–库仑强度准则能更好地描述冻结砂土的剪切强度。

线性变换应力空间及其应用

基于广义非线性强度理论,提出了一种新的变换应力方法,将广义非线性强度理论变换为另一应力空间内的Mohr-Coulomb准则。在新的线性变换应力空间内,材料的强度特性符合Mohr-Coulomb准则,从而广义非线性强度理论可在新应力空间内以Mohr-Coulomb准则的形式应用。通过在新的线性变换应力空间内对2种黏土的强度、应力-应变关系试验结果的分析验证了此变换方法的有效性。

基于1stOpt的强度准则的对比研究

Hoek-Brown强度准则和Mohr-Coulomb强度准则自提出以来,被广泛应用于岩石工程,但是由于它没有考虑中间主应力的影响,在理论和实际应用上存在不足之处。为此,许多学者对此问题进行了相关研究。俞茂宏、昝月稳等综合统一强度理论和Hoek-Brown强度准则的优点,提出了一种用于岩石的非线性统一强度理论。该理论考虑岩石拉压强度相差较大的特点,也考虑了中间主应力效应,并且其子午线是非线性的。文章将岩石非线性统一强度理论与Hoek-Brown强度准则和Mohr-Coulomb强度准则进行对比分析,探讨这些强度准则之间的关系。通过1stOpt软件对6种岩石的真三轴试验数据的拟合分析可知,岩石非线性统一强度理论与试验结果吻合较好,能够较高精度地评估岩石的真三轴试验强度。

平面应变状态下广义非线性统一强度理论的研究

基于广义Hoek-Brown准则的非线性统一强度理论不仅考虑了中间主剪应力效应及其区间性,而且将统一屈服准则、统一强度理论、岩石的非线性统一强度理论联系起来,对在三向应力状态下岩石的破坏特性比较适用。本文利用广义非线性统一强度对平面状态下岩石的强度破坏进行了研究,得到了基于广义非线性统一强度理论的包络线方程,分析了有效剪应力和内摩擦角随有效正应力的变化规律,讨论了中间主剪应力效应参数对剪切破坏包络线及内摩擦角的影响。参数分析结果表明:在平面应变状态下,有效剪应力随着中间主剪应力效应参数的增大而增大,而内摩擦角随中间主剪应力效应参数的增大趋于稳定。