Reliability Analysis Of Stability And Deformation In Deep Foundation Pit

In the area of foundation pit, the physical and mechanical parameters of soil have muchrandomness. The traditional fixed value analysis method has not considered the randomnessof these parameters and therefore the results of this method will have some uncertainty.Reliability-based analysis method can consider the randomness of these parameters and thecorrelation between them fully. So the results of this method will be more objective andaccording with the actual.At present, the reliability research of foundation pit is still in the initial stage and themain research results are concentrated on the shallow foundation pit supported with simplesupporting system. But the reliability research of deep foundation pit supported with complexsupporting system is in the blank stage basically. Therefore, the main works of this paper areshown as follow.(1) Based on the limit equilibrium theory of slope,the failure function and the calculationmodel of the most dangerous slip surface for the inner global stability of foundation pitsupported by the composite soil nailing are established with the circular slip surface method.With the mechanical parameters of soil as random variables, the partial derivative of thefailure function to all random variables is deduced. The reliability index of inner globalstability of foundation pit is calculated with the improved first order second moment method.So the reliability analysis method of the inner global stability of foundation pit supported bythe composite soil nailing is set up. Finally, the impact of the forces between strips, thevariability of mechanical parameters of soil and the position of soil layers on the inner globalstability of foundation pit are analyzed.(2) Based on the bar system FEM for beam on elastic foundation, the load incrementalmethod and the elastic soil pressure calculation model,the stochastic finite element calculationmodels for the deformation, the strength of supporting structure and the inner struts areestablished in foundation pit supported with much struts structure. With the shear strengthparameters of soil as random variables, the partial derivative of the excavation deformation toall random variables is deduced and the reliability index of the deformation, the strength ofsupporting structure and inner strut of foundation pit is calculated with the improved firstorder second moment method. Then the reliability analysis method of the deformation, thestrength of supporting structure and inner strut of foundation pit supported with much strutsstructure is set up. At last, the influence of the variability of mechanical parameters of soil andthe position of soil layers on the excavation reliability is analyzed.