ABSTRACT
Tunneling between Mandi House and ITO stations of DMRC involved tunneling underneath the existing Blue Line of Delhi Metro and the busiest corridor of the Indian Railway at Tilak Bridge. The absolute requirement for maintenance of operations, combined with the safe and economical construction of the tunnels, has mandated that the installation of tunnels be constantly evaluated. Two Mitsubishi Earth Pressure Balance Machines were chosen for this tunneling work and the precast lining of grade M50 concrete was used. The Blue Line Metro was located at 120m east of launching shaft, 30° skew with the tunnel alignment and Indian railway line was located around 500m east of launching shaft, 60° skew with the alignment. Trains run frequently on these lines, hence no track closures and reduction in the train speed was allowed through the project site. As a result, surface settlement and deformations had to be limited to negligible amounts during construction and over the lifetime of the structure. The tunnel was primarily excavated in Sandy Silt to Silty Sand. Groundwater depth was 4.7 m. PLAXIS was used for prediction of settlement analysis caused by tunnel boring. Soil volume loss was restricted to 0.3% to restrict settlements within permissible limits. Extensive Instrumentation and Monitoring was carried out and Alert Values were fixed.
