Numerical Study of using Diaphragm Wall to Mitigate Mechanized Tunneling Induced Settlements

Tunneling induced displacements could be dangerous for surface structures and urban infrastructure, if not controlled. Accordingly, different techniques are carried out to mitigate tunneling induced displacements. In this regard, using a diaphragm wall is a practical technique. In this study, the effect of using a diaphragm wall in mitigating the Madrid metro tunneling induced displacements was investigated. Despite mechanized tunneling of the Madrid metro extension, there is a considerable settlements due to a thick layer of made soil ground. In this regard, TBM-EPB tunneling of the Madrid metro tunnel has been modeled step by step and three-dimensional in the finite element code of ABAQUS. The main construction aspects of a TBM are modelled, such as the face pressure, the injection of grout behind the segments, the overcut produced by the gap between the diameters of the cutter-head and the shield. The diaphragm wall is also modeled three dimensional. Varied parameters of the study are the elastic modulus of the wall, the length of the wall, friction between the wall and the soil, the distance of the wall from the tunnel axis and the density of the wall. The results show the elastic modulus of the wall and the distance of the wall from the tunnel axis are the most effective parameters in mitigating of the tunneling induced surface settlements and horizontal displacements. In the distance of 0.7D between the wall and tunnel axis, a wall of 0.5D or C+1D length could be the optimum option to mitigate the settlements.