Study On Stratum Subsidence Of Shallow-buried Tunnels Crossing Through Existing Utility Tunnels

Shallow-buried tunneling method is one of the main construction methods of urban underground tunnels in China.It is widely used in underground crossing projects.In view of the limited underground space in the city,the planning of underground projects often presents conflicts on the nodes,which leads to the problem of the adjacent construction of underground projects.The settlement and deformation of overlying strata and existing structures caused by cross-cutting construction of underground tunnels has been the focus of domestic and foreign scholars in recent years.With the rise of the construction of urban utility tunnels in China,the subsidence of strata and existing utility tunnels caused by undercrossing tunnel construction is worthy of attention.Based on the existing theory of adjacent construction,combined with practical engineering cases,through theoretical calculation analysis and numerical simulation,this paper studies the influence of cross underpass engineering of shallow-buried tunnels on the subsidence of strata and existing utility tunnel.The main research contents are as follows:(1)Based on the actual working condition data and related engineering experience,the law of ground subsidence caused by crossing the existing utility tunnel in shallowburied tunnels is simulated and analyzed by using geotechnical finite element analysis software MIDAS GTX/NX.Focusing on the excavation method,section size,distance of cross underpass,cross angle and double-track effect,the paper makes a deep analysis of the influence factors of multi-construction,which provides a reference for the settlement calculation model.(2)Based on stochastic medium theory,considering the cross-section form of fivecenter circular horseshoe-shaped tunnel,the excavation of double-track tunnel,the structure of overlying utility tunnel and the angle of oblique cross-over of new tunnel,the existing settlement calculation formula is revised,and a settlement calculation model of shallow-buried tunnels crossing through utility tunnels is established,which integrates multiple factors.(3)The basic parameters needed for calculation of settlement model of existing utility tunnels crossed by shallow-buried tunnels are defined.A back analysis method based on Powell method to determine tangent value tan of main influence angle of stratum and uniform convergence value ? of tunnel section is given.GaussLegendre quadrature formula is used to solve the problem of settlement calculation model,and the corresponding calculation program is compiled by MATLAB calculation software to realize the numerical simulation of settlement calculation model.Comparing the calculated results of the model with the measured data,the reliability of the settlement calculation model is preliminarily verified.Finally,combined with engineering practice,the settlement control measures of shallow-buried tunnels crossing through existing utility tunnels are summarized.