Evaluating the effect of Top heading and Central diaphragm wall methods on the surface settlement and pile group

In urban areas with high population density, lack of surface space has led to the development of the transport network, especially the construction of underground tunnels, which is usually inevitable in the construction of buildings near deep foundations. When a tunnel is excavated, the surface settlements will result in damage to the surface and deep structures. Therefore, control of surface settlements and other environmental impacts is key to the design of tunnelling projects. Thus, in the present study, using the three-dimensional analysis by Abaqus finite element software, the effect of New Austrian tunnelling method (NATM) including Top heading (TH) and Central diaphragm wall (CDW) on the surface settlements and the forces applied to the single pile and the 2 × 2 pile group was investigated when the tunnel is adjacent to the piles in weathered residual soil. The results showed that the amount of net forces applied to the pile due to tunnelling patterns when running as a pile group was significantly lower than those for the single pile. It was also proved that, in the pile group, the CDW method created a lower amount of net surface settlements and net axial forces compared to the TH method. Also, unlike surface settlements, the influence zone on the pile head settlement in the longitudinal direction can be identified as ±2D in TH, and in the CDW method from -2D to +1D from the pile center (behind and ahead of the pile axis), where D is the tunnel diameter.