A section of Turins VAL metro is being constructed next to the city central station along a zone that is characterized by heavy traffic and a dense sewage network.In addition,the alignment in that part of the Line 1 Extension is characterized by a 55m-radius curve rendering impossible the use of a TBM.The design had foreseen pre-treatment of the ground with cement injections from the surface a technique that was expected to cement the cohesionless gravely ground.However,due to unpredictable geotechnical soil variability(sandy,silty and clayey lenses)and surface obstructions it was not possible to obtain uniform cementation of the soil causing critical over-excavation.In order to overcome this problem a new forepoling system was developed that consisted of self-drilling bolts injected with bi-eomponent silicate-based resins installed at the face of the tunnel along a 70 arch.The result was excellent,over-excavation and crown collapses were minimized with excavation advancing at a rate of 2～3m per day.