Study On Construction Stability Of The Underground Tunnel Hidden-digging Region In Shenyang

With the improvement of China's overall national strength, many big cities will be a member of the international metropolis, they will also accelerate the speed of the modernize construction, and subway construction which can ease the pressure on urban traffic will be the top priority. It is expected that the 21st century will be China's peak period of urban subway construction.Shallow undercutting was a method of tunnel excavation methods which appeared in order to adapt to urban's underground engineering which be lack of the conditions of Open-cut tunnel construction,and for its practicality and the superiority of certain aspects,its application became more and more widely. Because it mainly applicated in the urban's underground projects, the study on stability of shallow tunnel construction and its impact on the environment had a very important practical significance.Based on the examples of Shenyang subway engineering, for the purpose of protecting the self-stability of surrounding rock and guiding constructions, with the method that combined site monitoring with numerical simulation,the tunnel construction ability was systematically analysed in the aspects such as the deformation of surrounding rock, the settlement of the ground-surface, the stress of surrounding rock and the supporting structure,the plastic domain, this paper has concluded the settlement law of sandy soil layer of Shenyang region with construction,and maken the recommendations involved. In addition, for the geological conditions of Shenyang region, the paper has studied the impacts to tunnel with different construction methods, different size of excavation,the stagger distance between the double tunnels using numerical simulation methods,and optimized the construction plan.The main conclusions could be gained from what studied above:In Shenyang region, for the Co-double Tunnels in which the average thickness of the coveraged soil was 9.5 meters, the size was 6.28×6.5 meters,the distancce between two axises was 13 meters,it was feasible and reasonable to built city metro with the Bench method, the size of excavation was 1 meter, the length of bench was 3 to 5 meters, the stagger distance between the left-right tunnels was about 10 meters, as long as the construction method and measures were proper, the dynamic stability of the tunnel in the construction could be guaranteed; Reducing each excavation footage in construction of the tunnel can significantly reduce ground settlement and the level displacement of the soil; The affected area of the ground settlement of the water-rich sandy lawyer in Shenyang region was about five times of the hole's diameter,ground settlement caused by construction disturbance was in the value of roughly 30-40 mm, the proposed early warning value of ground settlement in Shenyang region should be 40 mm and above.The convergence displacement u is advised to be 1.36-14.20mm and the convergence ratio is advised to be 0.22-2.26‰.