Study On Pile Driving Effect Applying Cavity Expansion Theory And Finite Element Method

With the rapid development of economic, urbanization developed quickly, available earth in city become rare, so it became inevitable that buildings are constructed in dense city zone, which make it become an important subject that how to reduce the bad effect produced during construction, the bad effect caused by driving pile is severe, how to predict and reduce the effect on surrounding region would have theoretical and practical value. Cavities expansion and finite element method are used widely in studying pile driving effects, on the base of past researches, such two methods were improved by introducing more appropriate hypothesis and considering more completely the factors involved in pile driving.Firstly, by using the principle of the elasto-plastic theory and the outcomes of routine triaxial test, the soil was assumed to be a homgeneous, isotropic matrial obeying tri-linear and tetra-linear softering model that considered the yield strength was dropped lineary with strain the dilation was considered, the Mohr-Coulomb and twin -shear united strength theory yield criterion were adopted individualy, big strain theory and small strain theory were also considered, on all these supposes, analytic solution of spherical cavities expansion was got. the influence of wether or not to consider elastic deformation in plastic zone and test and softening parameters and big and small strain were analyzed.Secondly, on the suppose that the effect of pile driving was the accumulation of effects of a lot of sole spherical cavity expansion, on the base of the analytical solution got, by making use of a source-source and a source-sink imaging technique, a anlytical solution predicting the effect of pile driving was obtained.Thirdly, according to some shortcomings in simulation of pile driving by finite element method, on the idea of displacement penetration, finite element method was used to analyze the compacting effects of pile driving with the consideration of influence of initial stress and with the use of Mohr-Coulomb model. The influence of some factors were analyzed, the difference of whether or not to consider the initial stress was discussed, the variation of discipline of compacting effect with the the sink of pile was analyzed, the discipline of compacting effect of different length of pile was also analyzed.Finally, the discipline of distribution and consolidation of excess hydraulic pressure was simulated when piles were drived in saturated soft soil, the unified process of the dissipationof excess hydraulic pressure and the increase of effective stress and the decrease of heave of soil surface was discussed, the influence on discipline of consolidation of some factors of soil are analyzed.