Limit Analysis For 3D Overall Stability Of Unsaturated Slurry Trench

Concrete underground diaphragm walls are extensively used for deep foundation support owing to their excellent watertightness and high stiffness.During the first construction stage of a diaphragm wall,a trench filled with mud is excavated,followed by placing a reinforcement cage in the trench,and then pouring concrete into the trench.The stability of the trench wall is of great concern to geotechnical researchers and the industry,as the trench wall is potentially unstable during the trenching phase.Most of the existing studies have mainly focused on the stability of trench walls as a two-dimensional plane strain problem,due to the difficulty of constructing damage models for three-dimensional trench walls.However,the damage of channel walls in actual engineering often exhibits obvious three-dimensional characteristics,indicating that the plane strain damage mechanism does not accurately reflect the damage of slurry trench.Furthermore,current research work is primarily conducted in the context of saturated soils.However,in practical engineering applications,most soils tend to be unsaturated,and their mechanical properties differ significantly from those of saturated soils due to the influence of suction.In this paper,we investigate the overall stability problem of three-dimensional channel walls of diaphragm walls under unsaturated soils based on the limit analysis upper limit theorem.We propose a method to solve the safety factor of three-dimensional channel walls under unsaturated conditions,and investigate the stability problems of two-dimensional and three-dimensional slurry trench in both saturated and unsaturated soils and under complex conditions.This method provides some theoretical references for the design of continuous walls under unsaturated soil conditions.The main research of this paper is as follows:1)For the three-dimensional overall stability of the diaphragm wall under unsaturated land,the three-dimensional overall stability of the diaphragm wall under one-dimensional unsaturated seepage conditions is studied based on the upper limit theorem of limit analysis,combined with the three-dimensional rotational damage mechanism,and the expression of the three-dimensional safety factor of the diaphragm wall under unsaturated land is derived based on the energy balance equation.Next,the minimum safety factor and the most dangerous sliding surface are optimized using genetic algorithm,and the effects of three-dimensional effect,slurry weight,slurry level height,additional load,and relevant parameters on the stability of the underground diaphragm wall under unsaturated seepage conditions are analyzed in detail.2)For the problem of three-dimensional overall stability of slot walls in unsaturated soils with groundwater level variations,Michalowski’s pore water pressure power calculation is extended to unsaturated soils,and a method for three-dimensional overall stability of slot walls of subsurface diaphragm walls under consideration of groundwater level variations is proposed,and a comparative analysis with numerical simulation results shows that the method is reasonable and effective.Through parametric analysis,the effects of pore water pressure coefficient,depth of the channel wall,change of groundwater level and change of effective weight of the soil on the three-dimensional overall stability of the channel wall of the underground diaphragm wall are studied.3)A three-dimensional channel wall model of the underground diaphragm wall under unsaturated seepage conditions was established by using MIDAS GTX NX numerical simulation software,and the safety coefficients solved by numerical simulation were compared and analyzed with those solved by theoretical methods to comprehensively evaluate the overall stability of the three-dimensional channel wall under unsaturated land.