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Behaviors of the pile foundation due to groundwater level rising were analyzed by a series two-dimensional finite element analyses with fully coupled flow-deformation analysis. The different numerical models of single bore pile depth and diameter in Bangkok subsoil were represented with the parametric study. The pile–soil movement due to groundwater levels rising between numerical simulation and a previous experiment of the centrifuge test as the same condition are in good agreement. With rising groundwater level, the reduction of pile capacity can be evidently performed by the increase of pile settlement relative to soil surface. Moreover, the development of the plastic point captured by the finite element analysis revealed the mechanism behind the reduction of pile capacity. In this study, the evaluation of pile stability due to groundwater level rising for preliminary guidelines to protect existing structures are proposed.

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Underground structures are popularly utilized in urban development, especially tunnels for both transportation and utilities. The interaction problem between existing tunnel and piles from new constructed structures thus becomes unavoidable in dense population area. The tunnel loses its stability if the additional forces and changed diameters (due to adjacent piles under loading) of tunnel lining are drastically high. This depends on many factors, such as the clearance and pile tip level with respect to tunnel position. For preliminary assessment during the first stage of design, it is necessary to estimate this impact. The concept of tunnel protection zone is commonly adopted. However, to establish the tunnel protection zone for adjacent loaded pile, the understanding on this interaction problem is essential. This study analyzes the effect of adjacent pile under loading on the existing tunnel by 3D finite element method. The case study is the tunnel of MRTA project subjected to an adjacent 1 m bored pile under loading with various lengths and clearances. The additional forces ( bending moment and axial force) and the tunnel deformations are investigated. The results show that the additional forces and the tunnel deformations decrease when the clearance increase and become insignificantly increasing when the clearance is larger than 3.5 m. The distribution patterns of additional forces and tunnel deformation are similar.

Abstract. The effect of adjacent loaded pile row on the existing tunnel is analysed by 3D finite element method. The MRTA project is used as reference case in this study. The case study is divided into two cases, tunnel and pile tip located in soft clay and stiff clay, respectively. The pile diameter of 1 m and pile tip located at the elevation of tunnel crown with various number of piles within the row were considered. The analysis results are shown in terms of total soil displacement (without tunnel) and maximum tunnel deformations. Both total soil displacements and tunnel deformation increase with the number of piles and approach a maximum value when the number of piles is greater than 13 and 11 for cases tunnel in soft and stiff clay, respectively. This reveals that the tunnel deformation mechanism is primarily due to the soil displacement.

ABSTRACT:With the advancement of computer sciences and researches on tunneling simulation in the past, the 3D finite element analysis of tunnel excavation by Tunnel Boring Machines (TBMs) has been extensively used over the last decade. Due to that the complicated construction sequences and relevant loads can be taken into account, complex interaction problems can then be performed. Many simulation techniques have been proposed depending on the assumptions used in the modeling. For modeling the tunnel lining, solid elements are commonly used due to the ratio between the width and thickness of the lining is not large. In addition, most studies focused on the ground deformation, not the lining forces. In the circumstance that the lining forces are essentially observed, the structural elements that directly provide the values are preferred. Therefore, this research attempts to propose the shell elements as tunnel lining together with the grouting layer in the analysis. The analysis results from the proposed method and the conventional one are compared and discussed in terms of ground deformation and lining forces together with the field measurement data. The results reveal that the simulation by the proposed method is sufficient and can reasonably reproduce the soil and lining responses.

With rapid urbanization, large number of tunnels with various dimensions have been constructed for transportation and utility systems in many big cities. At the same time, the constructions of infrastructures using a pile foundation system are also necessary in urban area. With limited space, the existing tunnels can be inevitably impacted by the newly constructed pile-supported structures. With various design criteria of tunnel lining, the size and thickness are varied from project to project. With an adjacent pile under loading, different degrees of impact on these tunnels are expected. This study numerically investigates the effect of tunnel diameter and lining thickness on tunnel deformation due to adjacent pile under loading. The MRTA and WMA tunnels in Bangkok subsoil are chosen as the reference cases for investigation. From a series of parametric study, a relationship between the tunnel deformation and dimensionless parameter, which include the size and thickness of lining, can be successfully established.

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