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Abstract The increased demand for underground systems in urban areas has led to many tunnels being constructed close to existing structures. An indispensable prerequisite to successful tunnelling projects is to predict the deformation in order to avert any potential damage of building or buried utilities. The effects of tunnelling on pile foundation supporting these structures are therefore, of great concern. This thesis aimed to develop a better understanding of the problem and contribute to the design and analysis of pile foundations. The response of pile foundation due to tunnel construction is principally a three-dimensional (3-D) problem whether it is the tunnel advancement or the pile foundation. The analyses described in this thesis were performed using finite element program ABAQUS 6.11. This software provides the flexible features to model the details of tunnel construction in soils. Therefore a threedimensional finite element model to simulate the phase tunnel advancement including the application of excess face pressure, rate of shield advancement, over-cutting, and lining erection with activation of grouting material was developed to understand the pile response. All the soils, shield, tunnel lining, pile foundation were modelled using 20-noded continuum solid element. The main elements of the interaction such as; ground continuum, the piles, the pile caps, the precast lining segments, the tail skin grouting, the developed gap around TBM due to machine overcutting, and the TBM shield are modelled using prismatic solid element C3D20R, which is a three-dimensional 20-node hexahedra element with 8 integration points (reduced integration). The model boundary conditions are determined after conducting preliminary sensitivity analyses concerning its effect on the pile caps vertical displacements in terms of the tunnel diameter. Soil convergence around the tunnel excavation was modelled using a non-associated elastic-perfectly plastic Mohr-Coulomb failure criterion. The shield, tunnel lining elements, piles elements, and pile caps elements are characterized as elastic elements with different elastic properties to account for the different stiffnesses of the these elements. The tail grout used to fill the developed annular ground gap around the TBM due to tunnelling overcutting is updated simultaneously using solid elements. Therefore, calibration with measured surface settlement during shield passage was necessary. The elastic parameters of grouting material are determined according to the state of the setting of the grout from the liquid state to the hardening state in accordance to Mindess and Young, (1981). The process of tunnel was modelled in two steps; first, the initial conditions were set up for the model before excavation of the tunnel. It was achieved by specifying the distribution of effective vertical and horizontal stress (using coefficient of earth pressure at rest, K0=0.5). The initial conditions were completed with simulating the pile cap and its connected piles. After establishing the initial conditions, the analyses continued with modelling excavation of the tunnel Slurry shield tunnel boring machine. The 3D finite element modelling of the groundtunnelling-piling interaction is visualized taking into consideration the details of tunnelling activities and the rate of tunnel advance. Advancement of TBM was simulated simultaneously as follows; i) applying the excess face pressure, ii) removal of soil elements and activation of shield, and iii) activation of lining elements and grouting elements from the liquid to hardening state. This numerical model is verified by back analysis of field data obtained from two cases of studies. The first case considers of the stability of El-Attabe Garage building due to the execution of the Greater Cairo Metro Line 3-Phase 1, while the second case considers the stability of an existing motorway constructed of contiguous pile walls due to the construction Metro project in Shiraz city Iran crosses below the underpass. The valuable field monitoring data of the case histories was only limited to a specific range of tunnel-pile configurations, and tunnelling parameters. Further understanding of the tunnel-pile interaction problem outside the range is therefore required. To bridge the gap of knowledge, a set of parametric studies is implemented using three-dimensional (3-D) finite element (FE) model. Parametric studies are employing the calibrated finite element model of Cairo Metro tunnel to evaluate the effect of i) pile grouping, ii) pile cap rigidity, iii) the location of pile tip relative to tunnel centreline, iv) offset of pile cap from tunnel centreline, v) the effect of changing pile diameter, vi) the effect of pre-tunnelling loading, vii) the tunnel excess face pressure, and vii) the tunnel over-cut. The building stiffness is investigated using a hypothetical pile foundation having 100 piles. The followings can be concluded from this study in the next section. The results of the parametric studies are presented in the form of charts. Some of these charts illustrate the deformation developed in the pile in vertical, transvers and longitudinal directions while, the other curves outlined the bending moment and axial load generated along pile shaft due to tunnelling. These charts are vast improvement of tunnelsoil-pile interaction. It is to be noted that the following conclusion are drawn from the studied cases only. |