Analytical And Numerical Analyses Of The End-bearing Capacity Of Jacked Piles Under The Influence Of Tunneling Induced Ground Loss

This thesis presents a study of the interaction between tunnels and existing foundations of piles in urban areas.The study is conducted by using a simplified cavity theory and the finite element analysis.A process for estimating the end-bearing capacity of jacked piles by using a cavity expansion is presented,with explanations of the relevant mechanisms.A parametric study of the model parameters was carried out to evaluate their impacts on the pile end-bearing capacity.The results indicate that pile installation affects the initial confinement pressure of the soil and such effect decreases from the pile tip toward the elastic-plastic interface,and that the end-bearing capacity increases with soil cohesion,friction angle,and density.A procedure for estimating the effects of tunnel volume loss on pile end-bearing capacity by using a simplified cavity contraction theory is presented,with explanations of the relevant mechanisms.A parametric study is carried out to analyze the pile-tunnel interactions and the results indicate that tunnel volume loss may either enhance or reduce the pile end-bearing capacity,depending on the relative positions of tunnel and pile tip.Two-dimensional finite element analysis using PLAXIS is carried out;focusing on the effects of soil movements and stresses induced by tunneling on existing jacked piles and comparison with the analytical results are analyzed.Both compressive and tensile forces can be induced in a pile due to tunnelling,depending on the pile base location relative to the zone of influence.For a pile base located within the zone of influence,the pile is mainly subjected to tensile force.This is due to the relative movement between the pile and the soil around it.Both cavity and FEM analyses witnessed an increase of tensile stress on pile tip when Xtp>12.5m for FEM and Xtp>11m for cavity(casel);with an increase of tunnel-pile separation a compressive stress development on pile tip have been witnessed for both analyses.Magnitudes of compressive forces are generally small compared to ultimate pile capacity in compression.The effect of depth is also demonstrated that as depth increases for Case 2,the value of qb,vl/qb increases.The depth influences isotropic confining pressure.The method to estimate friction and dilation average angles is a function of the confining pressure.For case 3,both methods(Cavity theories&FEM)also agreed on impact of tunnel size on pile end-bearing capacity,qb,vl/qb decreases with an increase of tunnel radius which influences the size of influence zone(increase with tunnel radius).