Limit Analysis Of Seismic Slope Stability Considering The Tensile Zone In The Rear Part

Through field observation and laboratory experiments,it is found that the stability of the slope is influenced by the existence of tensile stress zone in the back edge of the slope,while the influence is amplified by considering the seismic load.In order to qualify the influence of the tensile stress on slope stability,two different mechanisms used at present are:(1)Introducing cracks in the rear of the traditional intact slope;(2)Reducing or eliminating the tensile strength of the soil,which is also known as tensile strengthcut-off.Based on upper bound limit analysis and pseudo-statics analysis,considering the influence of vertical acceleration,the slope stability parameters of the two failure mechanism can be derived.The sequence quadratic program(SQP)associated with a random searching algorithm,is utilized to find the upper bound results,which is faster and more accurate.In addition,based on the displacement coefficient with different combinations of parameters,the measured seismic waves,especially near-fault pulse-like ground motions,were input and the improved Newmark method was used to analyze the permanent displacements,the results show that:(1)The tensile stress reduces the slope stability and the earthquake loading amplifies this influence,especially for the case of the most unfavorable cracks and full tension strength cutoff.The tensile stress zone reduce the permanent displacements significantly.The results show that the permanent displacement of slopes with cracks five times the magnitudeof intact slopes;When considering the impact of vertical ground motion,it may generate greater permanent displacements.When the vertical seismic direction is downward,the maximum permanent displacement can be calculated.It can be observed that when ? varies from 0 to 0.4 for slope with tension strength cut-off,the displacement decreased exponentially with the increasing of ?.(2)The critical height of the 3D slope reduces due to the presence of cracks.A larger reduction in the critical height of slopes is found under plane strain conditions,compared to that under three-dimensional conditions.This reduction drops,however,with decreasing slope inclination angle.In addition,when compared with plane-strain conditions(slope width approaches infinity),the 3D slopes(with limited width)exhibit shallow sliding characteristics.(3)Near-fault pulse-like ground motions under different failure mechanism of the slope priduce much more permanent displacements than the near-fault non-pulse ground motions and far field motions with the characteristics of sliding fast and a short period of time accumulated a large amount of displacement.Aiming at this phenomenon,the pulse parts have been extracted from the original wave pulse.The influences of the pulse parts and the residual parts on the permanent displacement of the slope were respectively calculated and compared with the original wave.The results show: the pulse parts of the influence on permanent displacement of slope are very significant,and the permanent displacement even exceeds 50% of the original wave even in smaller PGA.The horizontal ground motion component is synthesized in different directions and the induced permanent displacement of the slope is calculated.It is found that the displacement generated by the vertical fault region is much larger than the direction parallel to the fault.