Three-Dimensional Physical Modeling of Response of Existing Metro Tunnel to Pile Loading in Delhi Silt in India

A nearby construction with a pile foundation in an urban area can cause possible damage or an operational safety concern to the existing tunnels. The response of the tunnel will depend on the relative location of pile tip as compared to the existing tunnel depth. This paper describes an experimental investigation carried out in the laboratory to examine the effect of pile loading on the existing tunnel in Delhi silt. A small-scale testing facility was designed and built to investigate the influence of pile loading in the close vicinity of the existing tunnel. Dimensions of the model tunnel and pile were arrived at based on the physical scaling laws. The model tunnel (outer diameter of 150 mm with thickness of 0.5 mm) and piles (outer diameter of 25.4 mm with thickness of 1.0 mm) are made up of aluminum. Tests were carried out in a fabricated model steel tank (1,100 mm wide, 1,600 mm long, and 1,200 m deep). Experiments were performed at various stages of pile loading at a separation distance of 1.0, 1.5, and 2.0 times the tunnel diameter from its axis. Results indicate that the strain in tunnel lining is significantly affected by various stages of pile loading when the row of pile is placed within the distance of 12 times the pile diameter from the axis of the tunnel. Three-dimensional numerical simulations of model experiments were also carried out, which fairly predicted the phenomena measured in the experiments.