Design and construction of scissor crossover tunnel in pune metro project

Majority of hydropower projects in India are in Himalayas which has fragile geology being young mountain. Recent rapid land subsidence in Joshimath has underlined the need of monitoring and controlling the surface settlements in-the influence zones of hydropower tunnels projects. In case of shallow overburden surface settlements will have greater-impact.

Design and construction of underground cavern in hydropower projects or crossover in metro tunnels involves fixing the size, layout and orientation of cavern or crossover, design of rock support, blasting pattern, excavation sequence, rock support, instrumentation etc. This paper discusses the challenges encountered during design & construction phases of shallow depth crossover NATM tunnel at Civil Court Station in Pune Metro project. It illustrates the way the problems of surface settlements due to tunnelling, heavy ground water ingress and natural big cavities partly filled with zeolites were handled successfully. The metro tunnels are designed and constructed at shallow depths for the convenience of the passengers. However, the construction of these shallow tunnels may lead to excessive settlement of the buildings and subsequent damages. Hence, the selection of alignment of tunnel and tunneling method in urban projects is crucial for the success of the underground metro project. The methodology adopted for construction crossover to control the surface settlements and heavy water ingress may be useful for construction powerhouse caverns.