Numerical Study On Interaction Between Subway Tunnels And Piles

With the rapid development of urban rail transit construction in China, it has become more popular that the construction of shallow buried in the city subway tunnel, road tunnel and the underground tunnel. Subway tunnel often have to go through the near pile foundation of existing structure, stratum stress redistribution happens because of the joint action of the pile load and the tunnel excavation, then tunnel excavation inevitably produces the surface subsidence and subsidence roof. It not only will cause deformation of the tunnel structure, but also cause the declining ability of the tunnel structure work. At the same time,it will also form plastic zone in the bottom of the pile and cave surrounding rock damage under pile load leading to affect the normal use.In this paper, we use FALC3D software simulation to study the effect of different factors on the subsidence and damage caused in the process of tunnel excavation under the pile road, It simulate and study the settlement of tunnel roof,ground and pile bottom cuased by different pile loads,then conclude the resulting settlement rule;Comparing which kind of way is more advantage after simulation the settlement of tunnel roof,surface and pile bottom due to three different excavation methods including the whole section method, three steps method and CD method;Simulation and analysis plastic range caused by tunnel excavation under different pile positions and concluding rules.The simulation results are as follows:(1) When the tunnel is located on the bottom of the pile, the farther distance of pile away from the tunnel center line, the smaller surface subsidence and the bigger roof settlement and the smaller pile-bottom settlement on the condition of the same distance from pile-bottom to tunnel roof under different pile positions; but when keeping the distance from the center line of the tunnel to the pile as constant,with the decreasing of the distance from tunnel roof to pile-bottom, the ground settlement is decreased, the settlement of the roof is decreased, the pile-bottom settlement is increased. When the tunnel is located on the side of the pile, the farther the distance of pile away from the tunnel center line, the bigger surface subsidence and the bigger roof settlement the smaller pile-bottom settlement on the condition of the same distance from pile-bottom to tunnel roof under different pile positions; but when keeping the distance from the center line of the tunnel to the pile as constant,with the decreasing of the distance from tunnel roof to pile-bottom, the ground settlement is increased, the settlement of the roof is increased, the pile-bottom settlement is increased.(2)In the two cases that tunnel is located in the bottom of the pile and pile side, the surface subsidence and roof subsidence and pile-bottom settlement caused by the whole section excavation is the most largest, the subsidence caused by three steps excavation is moderate,and the subsidence caused by CD excavation is the smallest.(3) When the tunnel is located on the bottom of the pile, the farther distance of pile away from the tunnel center line, the smaller pile-bottom plastic zone and the smaller tunnel cave plastic zone on the condition of the same distance from pile-bottom to tunnel roof under different pile positions; but when keeping the distance from the center line of the tunnel to the pile as constant,with the decreasing of the distance from tunnel roof to pile-bottom, the pile-bottom plastic zone is decreased, the tunnel cave plastic zone is decreased. When the tunnel is located on the side of the pile, the farther the distance of pile away from the tunnel center line, the smaller pile-bottom plastic zone but the tunnel cave plastic zone remain none on the condition of the same distance from pile-bottom to tunnel roof under different pile positions; but when keeping the distance from the center line of the tunnel to the pile as constant,with the decreasing of the distance from tunnel roof to pile-bottom, the pile-bottom plastic zone is increased, the tunnel cave plastic zone is decreased.