Three-dimensional Numerical Modeling Of Responses Of An Existing Pile Group Due To Tunneling

In many congested metropolitan cities, usage of tunnel become more popular forvarious proposes. However, construction of tunnels in such cities may induce excessiveground movements and tilting of nearby existing pile foundations. Therefore, it is necessaryto gain fundamental knowledge of tunneling-induced ground movements, tunnel headingstability and interaction of tunnel to nearby foundations. In this regard, various studies inthe literature have investigated the tunnel-soil-pile interaction by means of field monitoring,centrifuge and numerical modeling. However, the tunnel-soil-pile interaction is oftensimplified as being two-dimensional (i.e. the plane strain conditions) and the load transfermechanism between piles in a group has not been investigated systematically and wellunderstood.This study conducts three-dimensional, coupled-consolidation finite element analysesto investigate tunneling effects on an existing2×2pile group. The drained anisotropicstiffness parameters adopted in this study are taken from the data of the Queen Elizabeth IIConference Center at London. An isotropic model generally predicts a shallower and widersettlement trough than that predicted by an anisotropic model. Therefore, the soil ismodeled as anisotropic material in all of the analyses in this thesis.The construction of a6m diameter (D) tunnel in saturated stiff clay is simulated.Responses of the pile group located at a clear distance of2.1m (0.35D) from a tunnelconstructed at three different cover-to-diameter-of-tunnel ratios (C/D) of1.5,2.5and3.5are investigated. It is found that the most critical stage of tunneling for the pile group iswhen the tunnel face is close to the pile group rather than when the tunnel face has finishedexcavatingThe depth of the tunnel relative to the pile group has vital influence on theperformance of pile group. Tunneling near the mid-depth of the pile group (i.e. C/D=1.5)induces the largest bending moment in the piles, but the settlement and tilting of the pilegroup are relatively small. Based on a settlement criterion, apparent loss of capacity of thepile group is9.1%,23.7%and25.8%for tunnels constructed at depths of C/D=1.5, C/D=2.5and3.5, respectively. The largest load redistribution between the front and rear piles inthe group and the largest tilting of the pile cap towards the tunnel occurs when tunnelexcavated at C/D=2.5. The case C/D=2.5is found to be more critical than other twocases (C/D=1.5and3.5).