Slope failure at tunnel entrance due to excavation and its countermeasure

摘要

A large slope failure occurred at the arrival entrance of A-tunnel and the tunnel support linings were totally destroyed. The geological profile and the reason of the failure are discussed in detail. To complete the tunnel construction, firstly the fallen soil was removed and then a re-cut of the slope with a more stable gradient was carried out to assure the long-term stability of the cutting slope with rock bolts and shotcrete. The slope was cut with 15 stages and the total amount of the excavated soil reached 240,000 m~3. Furthermore, the entrance of the tunnel is redesigned and extended 40m using opening-concrete structure to avoid an eccentric earth pressure. As a counter weight, a retaining structure was also constructed to keep the stability of the riverbank that goes paralleled to the tunnel.