The Influence Of Pile Foundation In Life-Cycle On Adjacent Existing Tunnel

Beneath an urban environment there are many tunnels carrying road and railways.At the same time urban development involves the construction of high-rise buildingsthat require deep foundation. As a consequence, research on interaction betweentunnel and pile foundation has become an important task. It consists of two main areas:The influence of tunnel construction on existing piles; the influence of pileconstruction and loading on existing tunnels. However, there are only very fewpublications on the influence of bored piles on existing tunnels.In the present paper, it is aimed to further the understanding of the influence ofpile group on existing tunnels. The influence to tunnel from pile foundation iscompanied with the whole life-cycle of pile foundation. The paper was divided intothree main parts based on the life-cycle of pile foundation: influence of constructionof piles to tunnel, influence of the loading of pile group to tunnel and the influence oflong-term settlement of building to tunnel. The details are described as following:1. A method to simulate the influence of the wet excavation of a pile bore on anadjacent tunnel was introduced. In the analyses, the bentonite and wet concrete weremodelled by applying a hydrostatic pressure in the form of a total normal stressboundary condition within the pile bore. The changes of stress in nearby soil,displacement of soil, displacement of tunnel and internal force of tunnel wereobtained. The results showed that a large change of stresses of soil closed to pile bore,especially to horizontal stress. The changes of the lining displacement and internalforce were small. With respect of the whole construction process, a significantinfluence of pile boring to tunnel was happened after wet concrete crossing over thespringline of tunnel and hardening of wet concrete.2. The influence of pile groups loading on adjacent tunnel was investigated usingthe Analytical method and finite element method.(1) Based on the traditional shear displacement method, considering theinteraction between pile group and raft, the settlement of pile foundation andsettlement distribution in the soil around pile foundation could be obtained using theprogram developed in this thesis. With the certain settlement of soil which the tunnellies on, considering the stiffness of tunnel, the real reaction of tunnel to pile groupsettlement was given. The method presented in this thesis was able to do the calculation of large pile group with the real soil layer distribution. And it is flexible tochoose the interaction between pile and raft or not. Most advancement was that therelative location of pile group and tunnel could be any angle and distance.(2) The current paper assesses the influence of pile foundation on existingtunnels using the numerical simulation method with finite element program (Plaxis3D Tunnel 2.0). Firstly, the response of a tunnel to loading of piles located either onboth sides or on one side of the tunnel was discussed. Secondly, some parametricstudies including foundation layout, pile length, tunnel stiffness, pile loading level andclear distance between piles and existing tunnels based on the second relative locationwere carried out. Then a 2-D plane strain approach to analyze the loading of pile rowswas justified by 3D finite element method. Finally general design parameters (pilelength, pile location, pile distance and pile number) of shelter pile which can reducethe influence of pile foundation to tunnel were analyzed, to generate design charts forassessing reflection of shelter pile, which can give advices in practice.3. According to the odemeter test and back analysis of numerical simulation test,the creep parameters of muddy clay in Shanghai were obtained. Some discussionsabout the long-term settlement of pile foundation with the respect of rheology ofShanghai soil were carded out. The results showed that the settlement developed justafter the loading of pile foundation was about 75% of the final settlement. And thispercent was lower when the loading level applied to the pile foundation was higher.The settlement of tunnel developed slower than foundation settlement. The influenceof loading level to foundation was higher than to tunnel.4. the analytical results and the numerical results were supplemented with fieldmeasurement of the pile-tunnel interaction problem at a site named Pacific squareâ…¡in central Shanghai. It shows that the method which presented in this paper could getthe correct order of magnitude results comparing with the measurement data.