Study On Mechanics Of Construction And Structure By Numerical Simulation For Xi Aokou Twin-bore Tunnel

With the background about Xi Aokou twin-born Tunnels in Zhejiang province, the paper studies systematically and fully on the construction mechanical behavior of four lanes multi-arch road tunnel with width about 25 meters, combining with theoretical analysis and finite elements method (FEM) simulation.The main contains and research methods are listed below:First, Load-Structure Model is applied as the simulation way, disregarded of the support effects of the first lining, in another words when the first lining becomes invalid, the secondary lining stress is analyzed. Concretely, two methods are in the progress. First one makes the vertical stress balanced, which means the dead load above the invert equal to the headquarter of arch pluses the load of the structure which is suitable to the deep buried tunnels. The other takes the elastic foundation beams calculations i.e. open cut tunnels which is suitable to the tunnel with shallow depth and tunnels at loosened fragmentized surrounding.Second, 2-D FEM analysis is applied to simulate to construction processes and the stability of the terrain and the stress status of the primary lining is centering on.The achievements are shown below:First, the secondary lining is content to the design strength in the terrain ranking from II to IV, but the calculation moments, value in the crown, the joint between invert and foots are more magnificent than usual. The solution must be carefully considered, such as the shape of the structure and steel ratio.Second, no matter in what kind of the terrain conditions, excessive strengthening must be done during construction processes to the terrain of the middle wall to keep the stability of the middle wall. In weaker kind of terrain, the terrain of the spring must be strengthened.Third, in order to maintain the safety during construction, the excavation of the second main hole must behind the accomplishment of the secondary lining in the first main hole. And the distance of the two faces in different hole must be more than twice of the holes' diameter. Forth, the primary support system is fundamentally safety, but the strength of the shotcete must be operative. The construction must under the design, so that the safety of primary support can be maintained.