基于SLFT的边坡强度折减法失稳判据

A New Criterion of Strength Reduction Method for Slope Instability Based on the Slip Line-Field Theory

强度折减法在评价边坡稳定性时不需要假设和搜索临界滑裂面,相对于其它方法具有一定优势,但失稳判据尚无明确标准。滑移线场理论(SLFT)可以计算得到的极限状态下的边坡坡面曲线(简称极限坡面曲线),已有研究表明极限坡面曲线与边坡坡面的相对位置关系可以判断边坡稳定性。基于该结论提出一种边坡强度折减法失稳判据:不同折减系数计算得到不同的强度参数,因此滑移线场理论计算得到的极限坡面曲线将发生变化,当极限坡面曲线与边坡坡面在坡底相离时,判断边坡为稳定状态;当极限坡面曲线与边坡坡面相交于坡脚时,判断边坡为极限平衡状态;当极限坡面曲线与边坡坡面相交时,判断边坡为失稳状态。对标准边坡考题的计算结果表明:提出的失稳判据收敛性较好,安全系数计算结果与标准答案和已有失稳判据分析结论相差较小;传统失稳判据收敛指标的确定没有明确标准,当位移突变曲线光滑时很难找到突变点,很难准确计算对应的安全系数,更重要的是传统失稳判据判断边坡极限状态受到人为主观因素的影响,而提出的失稳判据可以实现失稳判据的客观标准化;确定的临界滑裂面形状以及在边坡中的位置都与标准答案基本一致,提出的失稳判据适用于强度折减法。

The strength reduction method(SRM)has an advantage over other methods in evaluating slope stability for automatically determining a critical slip surface.However,a key problem is that there is no corresponding definite standard for an instability criterion in using SRM.Previous research has shown that slope stability can be determined based on the relative position between the limit-state slope curve(referred to as the limiting slope curve)obtained from slip-line field theory calculations and the slope.Based on this conclusion,a set of new SRM-based instability criteria is proposed.The limit slope curve calculated by the slip-line field theory will change for different strength factors are calculated by different reduction factors.It can be concluded that the slope is in a stable state when the limiting slope curve does not intersect the slope at the toe.The slope is in a limit-equilibrium state when they intersect at the toe of the slope while the slope is in an unstable state when the limiting slope curve and the slope intersect.The calculation results of standard slope test show that when the new instability criterion has an advantage in convergence,safety factor calculated by the new criterion is close to the existing criterion and the standard answer.For the traditional criterion,there are no guidelines as to the choice of a tolerance criterion and the optimal number of iterations,and it is not always easy to find the sharp break point immediately after a slope failure,especially when the displacement curve is relatively smooth.Also,it is difficult to define a precise safety factor from this criterion,moreover,the evaluation criterion with a presumed allowable iteration number is influenced by an artificial factor.The objective quantification of the instability criterion can be realized by the new instability criterion.The critical slip surface shape and position determined by the plastic strain in the slope are basically the same as the standard answer.The new instability criterion is applicable for the strength reduction method.