Study On Construction Mechanics Of Municipal-Metro Tunnel Stacked Co-Construction In Riverside Area

In recent years,with the continuous development of cities in riverside area,the demand for urban railway transportation has increased.In riverside area of cities,the stratum,where metro shield tunnels lie,is often soft stratum with poor physical and mechanical properties.Besides,with the continuous construction of urban railway tunnels,the construction of tunnel near rivers and offshore and the proximity construction of multiple adjacent tunnels often encounter,which brings great challenges to the tunnel construction and operation.There is little research on the overlapping tunnel built near rivers,so it is necessary to deeply study the construction mechanics of the overlapping tunnel built near rivers,so as to provide a basis for the design and construction of similar projects.Based on the underpass project of Fuzhou Port Road and the tunnel project from Majiandu station to Chuanzheng cultural station of Metro Line 2,the engineering characteristics of the muddy soil layer of riverside crossed by the shield tunnel is studied through the methods of literature investigation,indoor geotechnical test and numerical simulation,the deformation law of riverside municipal Metro overlapping tunnel is analyzed by using numerical software,and the proximity influence zoning of riverside overlapping tunnel,reasonable construction sequence and the law of tunnel construction mechanics and structural deformation under the condition of groundwater fluctuation affected by tide are put forward.The main conclusions are as follows:(1)Through field sampling and laboratory test,the basic physical property indexes of typical soft soil and sandy soil in riverside area are measured.The results show that the physical and mechanical parameters of muddy soil and muddy soil mixed sand stratum in riverside area are similar.For such stratum with uneven spatial distribution,it can be simplified to the stratum with the same parameter in calculation.(2)The calculation results show that the seepage characteristics of soft soil and silt in the same stratum can be simplified by the coupling calculation method of soft soil and silt in the same stratum.(3)The construction sequence of overlapping tunnels has different effects on the structural displacement.In the environment with high water level,it is better to start the upside first and then the downside.The first excavated shield tunnel is the main reason for the surface settlement and vertical displacement of the structure.In the order from top to bottom,the deformation of rectangular structure increases with the increase of vertical clear distance between double track shield tunnel and rectangular structure.With the increase of horizontal clear distance between double track shield tunnels,the deformation of rectangular structure decreases.(4)For the construction of overlapping tunnels along the river,when the groundwater decreases,the settlement of the surface,rectangular structure and shield segment increases,the tensile stress of the main structure of the rectangular tunnel gradually increases and the compressive stress gradually decreases.The tensile stress and compressive stress of the segment increase gradually.From the perspective of reducing structural settlement and structural tensile stress,high groundwater level is beneficial.The periodic fluctuation of groundwater affects the surface settlement,the displacement and internal force of the main structure of the rectangular tunnel and the displacement and internal force of the segment,resulting in the periodic increase or decrease of different amplitudes.The structure has fatigue effect under the cyclic action.