Macro-scale And Meso-scale Study On Failure Mechanism Of Sand Retaining Wall

Much study concentrates on the earth pressure and the earth and water pressure acting on retaining wall, while litter study on failure mechanism of soil behind retaining wall. So the macro-scale and meso-scale study on the failure mechanism of the sand behind retaining wall is presented, at the same time the earth and water pressure considering the soil arching and seepage flow is also proposed in this dissertation.Soil arching and seepage flow is common phenomena in the soil behind retaining wall, their effect on the earth and water pressure should be considered. Assuming the shape of the principal stress arching as parabola, the soil arching behind retaining wall is analyzed. The seepage flow analysis is performed by solving Laplace equation with certain boundary condition. Then based on effective stress principal and horizontal different element method, the formulation of the earth and water active pressure acting on rigid retaining wall is performed considering soil arching and seepage flow effect. The calculation results are compared with the ones of model tests.It is show that the active earth and water pressure will increase and the point of resultant force will be move up along wall considering the effect of soil arching and seepage flow. The retaining wall's reliability and sensitivity is also analyzed, and sensitivity rules for retaining wall's reliability are obtained.Saturated sand retaining wall model system was developed to investigate the macro-scale and meso-scale passive failure mechanism of sand behind rigid retaining wall. The Variation of earth and water pressure distribution, displacement field, excess pore water pressure and shear band is obtained with different wall movement. There be different earth and water pressure distribution, displacement field with different wall movement model, and this is different from Coulomb theory's assumption that earth pressure distrubition is linar and the rupture suface is planar. The variation of excess pore water pressure shows that dense saturated soil has shear dilatancy, and loose saturated soil has shear shrink. The meso-scale experminent shows that with retaining wall translation, the sand particles in loacal position move forward along the one directin and rotate, then shear band is onset. It is also shows that the void ratios in shear band increase, the width of shear band is the dimater of 4-6 particles, and the angle of shear band is 40-50°. Based on experimental data, the opinion of three stages analysis of failure of the soil behind rigid retaining wall is presented. PFC2D model of the sand rigid retaining wall is used to study the meso-scale passive failure mechanism of sand behind rigid retaining wall. The passive movement of retaining wall leads to an increase and a rotation of principal stresses, and to different complex movement of soil particle. This is main reason for shear band. The movement of retaining wall plays a major role in the stresses field, the displacement field, the velocity field, the movement of particle and the shear band. It is simulated used the above PFC2D model that the passive and active pressure distribution behind rigid retaining wall under different modes of wall movement;It is also simulated used the coupled fluid-particle PFC3D model that the excess pore water pressure distribution in saturated sand behind retaining wall with translation. It is proposed that the coefficient of shear angle varies with the depth of wall, and soil mass is composed of rigid blocks with slip contact models, then the PFC2D model of retaining wall is built up to analyze the active pressure distribution behind rigid retaining wall with different modes of wall movement. All the simulation values are compared with the experiment ones.PFC2D model of the sand flexible retaining wall is used to study the deformation mechanism of foundation pit excavation. The influence of bending moment stiffness of wall and the depth of excavation on deformantion of foundation pit is assessed including deformation of and horizontal displacement of excavation supporting structure, the displacement of foundation pit soil.