DISTRIBUTION OF PLASTIC ZONES IN EXISTING TUNNEL DUE TO NEW CONSTRUCTION CLOSELY ABOVE THE TUNNEL AND THEIR MECHANISM AND REINFORCEMENT, A CASE STUDY IN BEIJING

Building a new station closely above an existing tunnel is a relatively difficult problem in underground construction. This paper uses numerical simulation methods and analyzes the distribution of plastic zones in the tunnel of the No. 1 Subway Line during the above construction of the Dongdan station for the No. 5 Subway Line in Beijing. It found that the symmetrical andrectangular distribution of plastic zones for the large-span station floor s influenced by existing line. Changing extent of different parts were also found on the plastic zones of the existing tunnel under backfill, sandy soil, clay interbedding,. The plastic zone valuesabout the side face of the existing line are the largest. Simulation on the reinforcement scheme was also conducted to guarantee the stabilization of the surrounding ground.