Limit Analysis Of Three-Dimensional Stability Of Unsaturated Inhomogeneious Soil Slopes Under Complex Conditions

The three-dimensional stability of slopes has always been a focus in geotechnical engineering.The current engineering design disciplines mainly focus on saturated soils,however,most of the soils are under unsaturated state in actual engineering and the mechanical properties differ greatly from those of saturated soils.In addition,because of long-time natural deposition and artificial excavation unloading and filling,the soil strength parameters in slopes usually shows inhomogeneity along with depth.Therefore,it is of great theoretical and practical significance to study the stability of three-dimensional slopes considering the unsaturated and inhomogeneous characteristics of the soil.In addition,seismic effect and groundwater activity are also the main external factors causing slope instability.In this paper,based on existing research,a series of studies on the threedimensional stability of unsaturated inhomogeneous slopes under complex conditions were carried out,and a limit analysis method for three-dimensional stability of unsaturated inhomogeneous slopes was established.The main research contents of the present study are drawn as follows:(1)Based on the upper-bound theorem of limit analysis,a three-dimensional rotational failure mechanism considering the toe,face,and base failure modes were established and the three-dimensional stability of unsaturated inhomogeneous soil slopes under one-dimensional steady seepage conditions was studied.An energy balance equation,which takes the effects of the suction stress,effective unit weight,and inhomogeneity of soil simultaneously into account was established,and the explicit expression of the slope safety factor was derived by the gravity increase method.The genetic algorithm was applied to search for the minimum of the factor of safety and critical slip surface of the slopes.The effects of width-to-height ratio,suction,effective unit weight,seepage conditions and soil inhomogeneity were studied through parametric analysis.(2)For the three-dimensional stability of unsaturated inhomogeneous soil slopes under seismic effect,a pseudo-dynamic approach was introduced to consider the spatial and time effect of the seismic waves and the amplification in seismic acceleration during the propagation in soil.The expression of work rate done by seismic force was also derived.For the special case where the water table intersects the failure portion below the slope toe,the suction effect induced by positive and negative pore water pressure was taken into account.The expression of safety factor was derived combining the upperbound theorem and gravity increase method and the minimum safety factor and corresponding critical slip surface were optimized by a genetic algorithm.The results obtained by pseudo-dynamic approach were compared with the results done by pseudostatic approach,and the effects of the horizontal seismic coefficient,pseudo-dynamic parameters,suction and the inhomogeneity coefficient on slope stability were discussed in parametric analysis.(3)For the three-dimensional seismic stability of soil slopes under water level variables,a three-dimensional horn-like failure mechanism for partially saturated inhomogeneous slopes was established.In the saturated zone of the slope,the external work rates done by pore water pressure and seismic force acting on the soil in the saturated zone were considered and in the unsaturated zone,the effects of water content changes on variations in suction and effective unit weight profiles of soil and seismic force acting on the soil in the unsaturated zone were considered.The expression of energy balance equation and safety factor were derived by upper-bound theorem and gravity increase method.The effects of suction,soil inhomogeneity and seismic force under water level variations on the safety factor and critical slip surface of the slope were studied through parametric analysis.