Instrumentation of a Road Tunnel Under Overburden Loading of a Four-Storied Building Structure, in Lonavla, Maharashtra, India

Maharashtra State Road Development Corporation Ltd. (MSRDC), India, is constructing a road tunnel 9 km long as part of the Mumbai Pune Expressway Missing Link Project in Maharashtra, India. The tunnel passes through heavily congested areas of Lonavla town wherein a number of building structures come near the alignment. However, a particular structure, a four-storied private building in Lonavla town, falls directly on the center line of the alignment of the tunnel and is just 40 m above the tunnel crown. Extreme detailed geotechnical designs were required for the estimation of the load transmitted on the Class C-type amygdaloidal basalt rock tunnel in order to dissipate the additional overburden pressure. FEM analysis was done for the design of initial and final supports. The tunnel was excavated in different parts heading, benching, invert, and multi-stages; after each excavation part, the tunnel contour was secured by means of rock bolts, sprayed concrete, wire mesh, and lattice girders. For building safety at ground level, the tunnel excavation pull was reduced to only 2 m for lesser vibration. Monitoring instrumentation was done with multi-point borehole extensometers, radial and tangential earth pressure cells, and bi-reflex targets. The monitoring instrumentation study for the utmost safety of the building is explained in this paper in detail.