Problems of shield tunneling for Beijing metro and solutions

Based on a detailed investigation and analysis, the present situation of shield tunneling for Beijing metro construction was studied. The main problems of shield method in the planning of the projects were as follows. First, continuous tunnel sections constructed by shield method were only a few; second, the efficiency of shield machine was low; third, the time used for non-driving tasks in shield tunneling was too long; fourth, the construction period using shield tunneling could not be guaranteed; and finally, the additional cost of shield tunneling was high. Detailed analysis indicates that the major cause for the problems was the contradiction of construction time between shield tunnel sections and adjoining stations, with the additional cause being that construction organization of shield tunneling was not well planned, that is the problem of shield machine passing the station was not well solved. A solution to the problems was put forward: let the shield machine pass a series of stations in the line first, and then construct the stations by cut-and-cover method or mining method at proper times. Such scheme shows great advantages in improving the quality, increasing the speed and reducing the cost of metro construction.