Supporting Design And Research Of Mine Metro Tunnel By Passing River In Wuhan Metro Line 3 Engineering

Tunnel excavation by mine tunneling method could cause rock-mass fracture and a relaxed state at the surrounding areas of the tunnel due to blasting. Hence, it is necessary to have support ready simultaneously when tunneling is carried out for the tunnel excavation by mine tunneling method. However, there are plenty of approaches to achieve support purpose and lots of factors to impact support scheme. Thus, construction scheme shall be adopted differently for various projects, so that a rational design for support scheme could be obtained according to project’s particularity.This paper, combining previous related research with Wuhan metro No.3 project as a real case study, make an analysis of the issues for support design at one of the intervals of crossing Han River.Firstly, construction method will be confirmed. Usually, mine tunneling method or shield tunneling method is adopted for tunnel excavation and different method is implemented to specific case with different formation conditions. It is discovered from the observation of the geological survey results at crossing river Section that the engineering section of the tunnel passes through a more rigid stratum and the geological formation at the back of the construction section is soft though. Therefore, shield tunneling method is adopted to conduct direct driving. In this project, mine tunneling method is adopted primarily for driving and shield machine is used afterwards by conducting empty push and segment assembly approach for construction purpose.Secondly, tunnel excavation by mine tunneling method could cause damages to wall rock instability. Thus, support should be properly arranged in a timely manner to avoid collapse from wall rock instability inside the tunnel. The initial common support approach used for tunnel excavation through mine tunneling method is always included advanced small pipe, suspension roof support, steel mesh, steel grille, sprayed concrete, etc. Then, the extent of geological conditions inside the tunnel could be determined through the data of the geological conditions of tunnel where it locates; besides, comparison could be carried out with the previous project examples to help select the appropriate support approach. By understanding these support schemes’ applications and referring to this project’s characteristics, the engineering analogy method could be adopted to acquire the final support scheme as the combined supporting for bolting and sprayed concrete. After support scheme is confirmed, numerical analysis will be conducted to work out supporting parameters, which are usually confirmed according to the engineering experiences.Lastly, mechanical calculation model can be established through ANSYS software for support scheme, proposed supporting parameters and other factors, so as to elaborate the influences that support scheme brings to earth’s surface and tunnel’s subsidence and analyze the impacts that the designed support scheme causes to wall rock; additionally, the credibility of the support scheme could also be confirmed through the analysis on the state of stress and deformation for bolting and sprayed concrete.