ABSTRACT
A novel Gaussian distribution function is used to model the ground volume loss around the tunnel periphery based on which an attempt has been made to predict the ground settlements by using linear elastic analytical solutions. A set of around 6 m diameter twin-tunnels spaced 6 m apart are being constructed in Kolkata using Earth Pressure Balance (EPB) Tunnel Boring Machines (TBMs) at a cover depth of around 20 m. The ground strata is predominantly silty clay, clayey silt with concentration of sand around the tunnel region. A ground volume loss of around 1-2% has been observed at different transverse sections on the tunnel alignment. Field monitoring reported after the tunnelling appears to conform with the analytical solutions. The disparity in the analytical and the field observations can be attributed to non-linear, anisotropic and non-homogenous soil behaviour around the tunnel opening. The simplicity of the solution allows it to be used by the engineers without having to go for complicated analytical and numerical solutions.
