Study Of Mechanism And Analysis Method Of The Instability Of Rectangular Diaphragm Wall Panel Trench

The slurry trench excavation technique has been widely used in Foundation Engineering for a long time, but the trench stability always is not being resolved well. Being short of understanding the factors influencing the excavations stability and instability mechanism, failure of excavations occurred occasionally. This paper, based on the result of former, centrifuge model test and failure example, investigates the key factors influencing the stability, expounds the instability mechanism form local and global stability and classifies the methods which used frequently on different definition of safety factor and subject investigated.This paper, using Lei's solution for calculating horizontal stress changes and displacements around an excavated diaphragm wall panel, puts forward semi-ellipsoidal sliding wedge to analyze the global stability, which covers the short of determining the form of sliding wedge in theory. Based on the limit equilibrium analysis of the semi-ellipsoidal sliding wedge, an analysis method is proposed for appraising the global stability of the panel trenches. After complied with Matlab, the method can analyze the influence factors behavior, such as water level, slurry level, trench length, distance extend behind the panel, length spread from the panel, soil unit weight, soil effective friction angle, soil effective cohesive strength, depth of tension crack zone, active earth pressure, overload and so on, which can obtain needed slurry unit weight under giving the needed safety factor. Though the calculation factors sensitivity and practical application, the method can give right law of influence factors and can appraise the stability of trench reasonably.There are a lot of methods to decide the stability of trench. In order to making different methods practical application clearly, this paper carries through comparatively study among them form different theory foundation, calculation factors sensitivity and practical application effect. Through the calculation factors sensitivity of former 9 m ethods, u nite t he c onclusion o f t his p aper m ethod c alculation factors sensitivity, the law of influence factors and problems have been found, the reason of the problems has been expound as well. Thought compare with two-dimension limiting equilibrium condition, the former result of FEM, centrifuge model and field, the semi-ellipsoidal, semicircle and triangular-prism sliding wedge can appraise the stability of trench reasonably. This paper method obtains a better-needed slurry unit weight. Through the study different parameter of this paper method, it is can find that this paper method can get a better effect in practical application, as the length spread from the panel is double of the distance extend behind the panel and the values of earth pressure influence coefficient is 0.5.