Influence of isolation pile design parameters on displacement of adjacent existing tunnels caused by foundation pit construction

In order to explore the influence of isolation pile design parameters on the deformation of adjacent existing tunnels caused by foundation pit construction, four sets of indoor model tests are first carried out under sandy soil conditions, including without isolation piles and with different distances between isolation piles and tunnels, and the influence of the location of isolation piles on the horizontal displacement and stress of the tunnel is analyzed. Based on the analysis of design parameters of relevant engineering cases, the value range of the main influencing factors causing deformation of adjacent tunnels induced by foundation pit excavation is determined, and 53 groups of single-factor mean clay analysis numerical models are designed, and the influence of various factors on the displacement of the adjacent existing tunnels caused by foundation pit construction is systematically analyzed. Research results show that the presence of isolation piles can significantly reduce the impact of foundation pit excavation on existing tunnels. The closer the isolation piles are to the tunnel, the better the displacement control effect; isolation pile length L, pit-tunnel distance D, ground connection wall thickness h, pile-tunnel distance d, foundation pit excavation depth H, tunnel burial depth B, and isolation pile equivalent thickness I are important factors affecting the horizontal displacement of the tunnel. The ground wall thickness h and the isolation column equivalent thickness Ⅰ increase linearly, and the foundation pit excavation depth H and pile-tunnel distance d increase linearly and as a power function respectively. The proposed multi-factor prediction model demonstrates high accuracy. The research results can provide references for the design optimization of isolation pile.