Effectiveness of Contingency Actions against Unexpected Ground Water Inflow in Urban Environment for Excavation of 48m Adit Tunnel

摘要

Conventional tunneling(NATM)in urban environment is always a challenge where surrounding buildings or structures are sensitive to settlement even though ground improvement usually serve as solution.In this case study,ground improvement from ground surface was not able to be carried out due to existence of multiple underground utilities.With mentioned restriction,chemical grouting was applied inside the tunnel during excavation.However,huge water inflow was encountered,and water table drawdown caused severe settlement within days.Additional chemical grouting was applied to refrain further settlement with continuous excavation.After the completion of excavation with water plugged off,water table recovered and 1/3 of settlement recovered.As a result,the effective conventional tunneling in urban environment is to limit water inflow and shorten the exposure period of the ground.