Study On Residuum Improvement And Shield Tunneling Parameters In Typical Strata Of Land-sea Interaction

The shield method has become the main construction method of modern city subway by virtue of its advantages of safety and speed.In shield construction,the soil is improved to achieve "plastic flow state",so as to meet the requirements of construction.Shield construction will damage the soil mass,cause surface settlement,and affect the safety of the surface and surrounding buildings.Therefore,it is an important link in the process of shield excavation to improve the residue according to the actual construction environment and control the parameters of shield tunneling.This thesis takes Tianjin Metro Line 11 as the engineering background,samples the typical strata of sea-land interaction(i.e.,water-rich soft soil layer,saturated liquefied soil layer and double-layer confined water layer),and carries out physical and mechanical tests on the soil samples taken out.Then,residual soil improvement tests are carried out on silty clay and silty clay in the tunnel section respectively,and appropriate improvement schemes are selected.A typical shield tunneling model was established to study the surface settlement law under different silo pressure and grouting pressure,and then the reasonable shield tunneling parameters were obtained.The main research conclusions are as follows:(1)Sample the typical strata of sea-land interaction,conduct physical and mechanical experiments on the soil samples taken out,and obtain the natural density,water content,pore ratio,liquid-plastic limit,permeability coefficient,mineral composition,particle size characteristics,pore structure and other parameters of the soil samples as well as formation characteristics.Considering soil parameters,stratum characteristics and environmental protection problems in the construction process,the active articulated earth pressure balancing shield is selected for construction.(2)Foam agent and bentonite in common residue improvers were selected to improve different soil samples in typical strata of the tunnel crossing the sea-land intersection.Relevant tests were used to determine the concentration of foam agent and bentonite mud,and the collapse degree was taken as the evaluation standard of the residue improvement effect.It was concluded that the modified agent combining foam agent and bentonite was selected for the clay silt.Foaming agent is selected as the amendment agent for silty clay.(3)Finite element analysis software MIDASGTS was used to conduct numerical simulation on three typical strata of land-sea interaction.In the simulation process,appropriate constitutive models were selected according to the relevant characteristics of different strata,and the soil bin pressure and grouting pressure in the process of shield tunneling were changed to study the influence of the two on the surface settlement and the difference of the settlement of different strata.The simulation results show that the silo pressure and grouting pressure are negatively correlated with the surface settlement.(4)In the construction of shield tunneling parameters proposed by numerical simulation,the field monitoring data are collated.The surface settlement curves drawn by the field monitoring data and the simulated data are similar,and the settlement values of the two data are consistent.The numerical simulation is credible and the shield tunneling parameters proposed by numerical simulation are feasible.