Study On Construction Deformation And Stability Technology Of Space Intersection Structure Of Underground Tunnels Group In Extra-long Highway Tunnel

In recent years,as the economy continues to rise,the highway network continues to expand,and the number of mountain tunnels increases unceasingly,including a mass of extra-long tunnels.In order to ensure the unhindered ventilation of the extra-long mountain tunnel,it is indispensable to construct a ventilator room to deliver fresh air through the air supply duct and emit vehicle exhaust through air exhaust duct,which will inevitably result in the cross structure of underground space with the air connecting duct crossing the main tunnel.Funiu Mountain extra-long highway tunnel project which this paper relies on is complex,the number of underground tunnels is large,the distance between the bottom of the upper-span air duct and the vault of the main tunnel is small(<2m),so the excavation of upper-span air duct will cause disturbance to the nether tunnel.Based on this background,this paper conducts a systematic study on the deformation and force characteristics and influence range of the main tunnel during the construction of the upper-span air duct by carrying out field monitoring tests and finite element analysis,and the following conclusions are obtained:(1)The consequences of field monitoring test and numerical simulation indicate that the initial support in the cross section of the existing main tunnel rebounds and heaves after the excavation of the upper cross air connecting duct,which resulting in the phenomenon of floating up,and the vertical deformation forms a "reverse settlement trough" along the tunnel axis,and the heave value of the same section gradually decreases along the vault downward.The horizontal convergence value of both sides of the wall is tiny,which changes with the excavation process,and the influence is tiny.The surrounding rock pressure and the endogenous force of supporting structure decline with excavation,while the side walls increase significantly.(2)Compared with the full-section excavation,the two-step method,two steps plus reserved core soil method and three-step method can effectively reduce the deformation of the main tunnel,but the difference between the latter three method is not large.The plastic deformation area of surrounding rock of the two-step method is larger than the latter two steps method,and the construction safety is low.So the two steps plus reserved core soil method is adopted as the most safe,efficient and economical method after the comprehensive consideration.(3)The influence of the construction of the upper-span duct on the initial support of the existing tunnel is mainly within ±5m from the centerline of the passage along the axial direction;the arch foot on both sides of the tunnel cross-section structure is more stressed.Due to the small spacing,the surrounding rock at the location of tunnel arch has poor stability,and should focus on strengthening the vault and the arch feet on both sides within 5m from the center line of the passage.