Research On Metro Rapid Construction By Mining Under Shallow Cover Method And Analysis Of Soil Stability

The urban development is restricted by land and the environment with the growth ofsocial economy and the increase of population. Traffic congestion is a big trouble for a citywith millions of or even billions of population. People live in metropolis will have such afeeling that although with the well developed transportation networks, the traffic condition isnot satisfied because of the high population density. To solve the problem of traffic congestion,the city has to adopt multiple developing trends and explore underground spaces.In2005, a city began to build subways. Metro Line1has been open to traffic. It isexpected the mileage of the City Metro will reach137.9km by the end of2013whichincluding inter-city rail traffic17km. The construction of tunnels in the crowded cities willinevitably disturb the soil which may cause strata deformation. If the deformation is too large,it will affect the ground buildings and structures. When the strata deformation reaches acertain extent, it will threaten the safety of the buildings and traffic transportation. Thereforethe subsidence caused by the construction and excavation of the tunnels, especially the stressfield and displacement field of the rock caused by the rapid construction of the tunnels underthe city main roads have become a big concern.Quick excavating footage and tunnel stability are investigated by numerical analysis.Adopting shallow underground excavation method in sandy soil layer is to ensure the safetyof the project and the rationality of economy. The construction speed can be improvedthrough the auxiliary measures. Excavation footage has become the key point in constructionprocess. Quick excavation has practical significance to shorten the work time and lower theproject cost. A reasonable evaluation index was lack of in subway tunnel stability evaluationof the, while the traditional finite element method can’t work out of the tunnel engineeringsafety coefficient and surrounding rock failure face. It was difficult to determine the safetyfactor of the tunnel of failure face rely on stress, displacement and the plastic of the area size. Tunnel stability analysis provide security theory basis for other routes of tunnel quicklyexcavation.Modeling of rapid construction was set up using finite element software. Thedisplacement, stress and plastic zone was contrast analysis. Feasibility of fast construction insandy soil layer footage was confirmed.Numerical analysis on the double tunnel fast excavation was carried out.Tunnelexcavation of the actual construction process was simulated, analysised two aspects whichincluded displacement and stress. Adaptabilityof quick excavation in sandy layer was validated through the comparison with the data measured displacements.The stability of process of tunnel excavation was judgement through the measurementdata analysis. To strength reduction principle as the foundation, safety coefficient of reservesof tunnel excavation was calculated, and concludes the development regularity of surroundingrock of plastic zone.This paper is based on the project of the city north line Metro, using numericalsimulation and measured data to analysis the quick excavation and the stability of the tunnels,study the deformation rules of the tunnels built in sandy soil layers during the process of therapid construction and obtain the safety reserve coefficient.