Analysis And Grout Control Measures For Settlement Induced By Shield Tunneling In Soft And Hard Composite Strata

With the advantages of saving space,carrying capacity,punctual and fast,urban subway has become a big weapon to relieve the pressure of urban traffic.Shield construction technology is mature,the construction speed is fast,the economy is high,the influence on the surrounding environment is small,and it is not easy to be interfered by external factors,so it has been widely used in the construction of urban subway.Soft and hard composite stratum is a kind of complex stratum encountered during construction.There are both soft soil and hard rock in this stratum,and the soil properties of the soft and hard strata are greatly different.Compared with the homogeneous stratum,the factors and rules of ground subsidence induced by shield construction in soft and hard composite stratum are more complex.Therefore,it is of great significance to study the influencing factors and settlement rules of ground subsidence induced by shield tunneling in soft and hard composite strata,the influence of sideway through adjacent buildings under such geological conditions,and to put forward effective measures to control ground subsidence and building deformation.The main research work of this paper is as follows:Relying on a soft hard compound formation metro shield tunneling engineering,according to the exploration data and construction materials,finite element analysis software ABAQUS is adopted to establish the double shield tunneling three-dimensional model,this paper introduces the numerical simulation of the basic assumptions,the size of the model,the basic step to set up and the construction sequence information,such as analysis of the numerical simulation of displacement and stress results,By comparing the simulation results with the actual monitoring data,the correctness and reliability of the finite element model are verified.In order to analyze the main factors of ground subsidence induced by shield tunneling in soft and hard composite stratum,the construction technology of earth pressure balance shield tunneling is introduced and the characteristics of ground subsidence in each stage of shield tunneling in soft and hard composite stratum are analyzed.It is concluded that the surface subsidence is mainly affected by such factors as the distribution form of soft and hard layers,mechanical properties of soft soil of surrounding strata,supporting force of tunnel surface,grouting pressure of shield tail,mechanical properties of equivalent layers,tunnel burial depth and spacing.Then,the action law and action degree of each influencing factor are obtained by numerical simulation results.The three-dimensional numerical model of shield tunnel side through frame structure in soft and hard composite stratum is established.The influence of two factors,the horizontal distance L from the building axis to the center line of the double-line tunnel and the buried depth H,on the surface settlement,foundation settlement,foundation settlement difference and inclination of the building are analyzed and revealed.In ABAQUS,two settlement control measures of grouting reinforcement in the soft soil layer above the tunnel and the soft soil layer around the tunnel are simulated.The effects of these two control measures on surface settlement and building deformation are compared.The reasons for different effects are analyzed from the perspectives of vertical stress and vertical displacement.It is concluded that the shield tunneling in the soft soil of tunnel surrounding rock is a more effective measure to control the ground subsidence.