Numerical Simulation Analysis Of Excavation And Support Of Foundation Pit With Three-Dimensional Fast Lagrangian Method

Foundation pit engineering is a complex, systematic and uncertain issue in geotechnical engineering. Among numerical simulation methods of excavation and support of foundation pit, traditional 2-dimensional FEM can only be applied in some particular circumstances to simulate the excavation and support process of foundation pit, so it can't meet general demands; 3-dimensional FEM involves tremendous matrix computation and consumes so much computer resources, so it can't be well performed on personal computers; meanwhile, current FEM can't take into account the influence of seepage effect of underground water on soil strength and soil-structure interaction effectively. Furthermore, FEM is incapable of dealing with plastic flow and large deformation after the failure of soil materials around the foundation pit. However, 3-dimensional fast lagrangian method is capable of simulating 3-dimensional mechanical behaviors of geotechnical or other materials such as yielding, plastic flow, softening or large deformation, especially suitable for gradual failure analysis, instability analysis, large deformation analysis and construction process simulation, furthermore, it can take into account the seepage effect of underground water and soil-structure interaction.Based on research results of other specialists, current numerical analysis methods in geotechnical engineering are discussed; meanwhile, fundamentals of 3-dimensional fast lagrangian method such as numerical equations of constitutive model of geotechnical materials and support structure elements are introduced. Combined with numerical simulation software FLAC~3D, the failure mode and its distribution regularity of soil around foundation pit are analyzed. Soil surface settlement distribution regularity and its influence scope, the deformation regularity of foundation pit wall in length direction and depth direction in excavation process with support and without support, the seepage effect of underground water and its influence on soil strength and soil-structure interaction are also analyzed.Research indicates that the excavation and support of foundation pit is a complex 3-demtentional spatial issue, which is closely associated with the properties of soil around the pit and support structures. In the excavation and support process of foundation pit, the spatial effect of soil and support structure, soil-structure interaction and the influence ofseepage effect of underground water on foundation pit are evident; meanwhile, it also indicates that 3-dimensional fast lagrangian method is a powerful tool for foundation pit engineering. This method should be widely used in geotechnical engineering in the future.