| In the construction of large-scale urban rail transit in recent years,urban subways have been widely loved for their large carrying capacity,punctuality,and lack of space on the ground.According to statistics,in 2018,the number of new subways has exceeded 1,000 kilometers.With the ensuing difficulties in the construction of subways,such as deep burial,large sections,and complicated geological conditions,it has become a major concern of experts and scholars.Therefore,under the influence of continuous blasting construction and excavation unloading,it is studied how to reduce surface settlement to ensure construction safety and speed up construction progress,which not only has high value in academic field,but also in actual urban subway.Construction has important engineering significance.This paper takes the super-large section shallow buried tunnel of the wrong section of Qingdao Metro Line 4 as the research object.The tunnel is constructed by double-layer initial arch method,and the tunnel model is used for three-dimensional display using BIM technology.In the theoretical analysis,the linear regression analysis based on the measured data is used to derive the settlement coefficient width i and the formation loss rate Vi suitable for the special geology of the faulty station,and then the Peck modification formula that can be used in the Qingdao area is obtained.The factors causing the surface settlement are analyzed one by one,and the settlement of the arch settlement with the greatest influence is deduced.The rationality of the formula is verified by the measured data.The MIDAS/GTS/NX finite element analysis software was used to simulate the whole process of construction,and the surface settlement,internal displacement of the tunnel and surrounding rock mechanics were analyzed at each step of the tunnel excavation.Compare the simulation results with the measured data,find the weakest link in the construction process through simulation,and carry out corresponding reinforcement measures.By designing three sets of numerical simulations for comparison,the methods of controlling surface settlement and speeding up the construction progress were found from the perspective of construction technology,and the feasibility andapplicability of the improved method were described.The main conclusions of this paper are as follows:(1)Through reading and analyzing a large number of domestic and foreign literatures on surface subsidence,the causes of surface settlement caused by large-section shallow buried tunnels and the difficulties that may be encountered during construction are summarized.The application of BIM technology to establish a three-dimensional model of the tunnel for display,and the advanced geological prediction as an important means to study the effects of underground cavities and fissures on surface subsidence.(2)Combining the measured data to theoretically analyze the ground settlement,and derive the Peck modification formula suitable for Qingdao Geology,in which the settlement groove width coefficient i=6.57 and the formation loss rate Vi=0.54%.In the prediction analysis of arch settlement,the settlement prediction formula is derived based on the measured data.In the difference analysis of surface and vault settlement,the vault settlement is regarded as one of the factors of surface settlement.In addition,factors such as precipitation consolidation,stratum loss and underground drainage have caused surface subsidence to varying degrees,and comparative analysis Reasons for differences in surface settlement and building settlement.(3)This paper selects the section with perfect monitoring data of tunnels with shallow depth,large tunnel section and surrounding buildings in Qingdao Metro Line4 as the target area of ??the study.It is established by using MADIS/GTS /NX finite element analysis software.A three-digit numerical model with a width of 120 m,a height of 100 m and an excavation length of 60 m.The three-dimensional dynamic simulation of the double-layer initial arched tunnel is carried out according to the construction procedure.The variation of the displacement,stress and plastic zone size and distribution during the excavation of each tunnel and its influence on the ground settlement are obtained.The stage of maximum settlement during construction is the excavation period of the upper guide tunnel.The maximum surface settlement and the settlement of the vault are 16 mm and 19 mm respectively.The simulation data and themeasured data are compared and analyzed,and the same settlement trend and similar are obtained.Settling size.(4)Three numerical analysis models of different working conditions are constructed,which are: three steps of initial support lag construction,different tunnel excavation sequences,double-layer double-side guide pit method and actual scheme.The results show that the initial settlement of the construction will greatly affect the surface settlement during the excavation of the upper section,which will increase the settlement data by 20%,but the impact on the whole construction period is small;Shorten the construction period,but increase the settlement and excavate the core soil will cause stress concentration on both sides of the soil;the double-layer double-side guide pit method is the best choice for settlement control,but it will greatly increase the construction period,which is not conducive to the subway.Rapid advancement on a large scale. |
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