Three-dimensional Upper Bound Analysis Of Stability Of Slope Containing Sand And Gravel Layer Under The Load On The Top Of Slope

In the strata of Xiangjiang river,sandy gravel layers are common.According to the composition of gravel and clay,the strength index of sand and gravel layers varies greatly.This kind of slope is simplified to homogeneous soil slope analysis.Due to the different failure mechanisms,the calculated results are bound to differ greatly from the actual ones.According to the failure characteristics of the interlayer slope with sand and gravel,the three-dimensional rotation and translational failure mechanism of the interlayer slope with sand and gravel is constructed in this paper.On this basis,based on the upper bound limit analysis,the strength reduction principle is adopted to obtain the solution equation of the safety factor,and the optimization solution of the safety factor is calculated through Matlab programming.At the same time,Optum G3 software is used to model and analyze the slope containing sandy gravel layer under the load on the top of the slope,and the safety factor and three-dimensional failure mechanism are obtained.Through comparison and verification,it is proved that this method is reasonable to analyze the three-dimensional stability of the slope with sandy gravel layer under the load on the slope top.And this method is adopted to analyze the engineering instance.The following results have been achieved.(1)According to the failure characteristics of the slope containing sandy gravel layer,the influence of the top load area on the width of the failure mechanism of the slope is fully considered,and the failure width of the top of the slope is limited to the area of the top load.Finally,the three dimensional rotational and translational failure mechanism suitable for the slope containing sand and gravel is obtained.(2)On the basis of the upper bound limit analysis,the strength reduction principle is adopted to obtain the solution equation of the safety factor,and the optimal solution of the safety factor is calculated through Matlab programming.The influence of four parameters which include slope load P(k Pa),slope degree?(°),dissection thickness H₂(m)and dissection position H₁/H on the slope safety factor F_S is analyzed.Compared with the calculated results of Optum G3,this method for three-dimensional stability analysis of the slope with sandy gravel layer under the load of the top of the slope is verified.(3)The modeling of Optum G3 is to explore the failure mechanism and safety factor corresponding to different soil strength parameters of slope interlayer,and the corresponding failure mechanism is obtained by reducing the strength parameters of the interlayer soil.The results of the safety factor show that once the failure mechanism changes from toe failure to bottom failure along the interlayer,the rate of decrease of the safety factor will increase.(4)Three methods which are three dimensional rotation and translational failure mechanism,upper limit finite element software Optum G3,and Swedish division method are used to analyze the stability of the foundation pit slope of the road engineering at the east of Luotangwan.According to the existence of heaped load of soil load on the slope top in this project,the limit value of the load on slope top is calculated.Meanwhile,the stability of the slope of the foundation pit is verified with the Scene monitoring data.The results show that the three-dimensional upper bound limit analysis method is available for the stability analysis of the slope with sandy gravel layer under the load on the top of the slope.