Numerical analysis of the influence of pre-submergence of foundation pits on adjacent existing tunnels

Construction such as foundation pit precipitation and excavation can lead to redistribution of stresses in the soil, which can affect the adjacent existing tunnel and even cause cracking of the existing tunnel. Using a foundation pit in Nanchang as a case study, a numerical model was established using PLAXIS 3D software to investigate the effect of pre-submergence of the foundation pit on the adjacent existing tunnel, and the influence of factors such as the burial depth of the existing tunnel and the distance d between the tunnel and the foundation pit on the tunnel deformation was discussed. The results of the study show that as the depth of the tunnel increases, the tunnel deforms in the direction of the pit, with the bending moment, horizontal and vertical displacement of the tunnel being “large in the middle and small at the ends”, and the maximum value of the displacement decreases gradually, while the maximum value of the bending moment. In addition, when the burial depth is less than 1.0H, the influence of the spacing d is the greatest, the larger the spacing d the smaller the displacement value of the tunnel; while when the burial depth is greater than 1.0H, the burial depth becomes the main factor affecting the tunnel deformation.