Evaluation of tunnel jacking induced ground surface heave

摘要

A 93m long concrete box tunnel was jacked underneath a tollway to provide an additionalrnroadway for the crossing traffic. The geotechnical conditions were predominantly residual soils, with stiffer soilsrnfound in the tunnel exit area. During half-way of the jacking process, the pavement above the tunnel showed somernsigns of heave, causing disruptions to the traffic. This paper reports the results of numerical analyses performedrnto examine the probable cause of the observed heave in order to avoid similar problems to occur in the future.rnPlane strain finite element models were developed to simulate the tunnel jacking process. Three aspects werernevaluated, namely the effect of different excavated soil conditions inside the box tunnel, the effect of jackingrndisplacement, and the effect of inclined stiffer soil. It was found that the ground surface heave is dependent onrnthe amount of soils excavated inside the box tunnel, which is in turn related to the required jacking force. Allrnthese observations would suggest that, to minimize ground surface deformation, it is important to maintain arnrelatively low jacking force.