Research On Spewing Mechanism And Migration Law Of Conditioned Soil In Water-rich Sandy Strata For Earth Pressure Balance Shiled

At present,the development speed of urban rail transit is increasing day by day,and it is inevitable to carry out construction in harsh terrain environment.Shield construction is the preferred method in the process of underground space development.As shield technology is widely used in the basic construction of subway tunnels and highway tunnels in major cities,the scope of application is expanded,and the tunnel will pass through various ground conditions.Among them,the water-rich sandy strata is characterized by poor particle gradation,large porosity,poor flow plasticity,large internal friction angle,low cohesion,and high permeability,when the earth pressure balance shield crosses the strata,it is easy to occur the phenomenon of"spraying" and the construction problems of poor slag discharge make it difficult to ensure the normal excavation of the shield machine,and even cause major disasters such as instability of the excavation surface and surface settlement.Therefore,carry out the analysis of the"spraying" mechanism of the earth pressure balance shield passing through the water-rich sand layer and the research on the migration law of the improved slag in the screw conveyor.For the analysis of the spraying and poor slag discharge when the shield passes through the water-rich sandy strata,etc.The cause of the problem,the guidance of on-site construction,and the ensuring of the stability of the tunnel are of very important engineering and social significance.In this paper,taking the Nanchang Rail Transit project through the water-rich sand layer as the background,in response to the "spraying" phenomenon,poor slag discharge and other engineering problems,the "spraying" mechanism of the earth pressure balance shield through the water-rich sand layer was developed Analyze and improve the migration law of the soil in the screw conveyor.The main research contents of this paper include:(1)Through the method of subsection analysis of soil tank and screw conveyor,finite element and analytical methods are used respectively to derive the head distribution equation of soil tank and screw conveyor,and the results are compared and verified with existing research.According to the calculation of typical shield parameters,the sensitivity analysis of shield mechanical parameters and soil parameters was carried out,and two major measures to prevent gushing were proposed,namely mechanical modification and adding modifiers.(2)Considering the influencing factors of sand permeability,through porous media seepage theory,gradation optimization and microstructure analysis methods,the impact of foaming agent,bentonite,and high polymer polymer on sand permeability is analyzed.The mechanism of improving sand permeability is analyzed from different angles,which provides a theoretical basis for the selection of adaptive modifiers for water-rich sand tunnel engineering.(3)Designed and carried out the conditioner optimization test,obtained the optimal foaming agent solution concentration and corresponding performance parameters,and used it in the permeability test and slump test to obtain the influence law of conditioner concentration,injection ratio,high molecular polymer content,etc.,on sandy permeability and fluidity.comprehensively consider the influence of sandy soil fluidity,permeability and economic benefits,obtained the optimal condition program that adapted to the formation.(4)From the theoretical point of view,derived the earth pressure gradient formula of the screw conveyor and the formula of the discharge soil flow rate.Analyzed the parameter sensitivity of the formula.The results show that the mechanical parameters of the screw conveyor and the property parameters of the slag are both important influencing factors of the slag movement of the earth pressure balance shield.Therefore,it is necessary to rationally design the mechanical size of the screw conveyor,and also to use technologies such as soil condition to adjust the properties of the muck,so as to ensure the smooth discharge of the shield and the efficiency and safety of the tunnel construction.(5)Through theoretical methods,analyzed the governing equation of the flow of the improved slag in the screw conveyor.Combined with numerical simulation,used combination of sliding grid and static grid,simulated the movement of the condition soil in the screw conveyor by Fluent.That verified the adaptability of the condition plan.At the same time,the engineering application shows that used the condition plan proposed in this paper,during the tunneling process of the shield machine in the water-rich sandy layer,various working parameters are stable and no spraying phenomenon occurs,indicating that the effect of soil condition is significant,which ensures the safety and efficiency of tunnel construction.The research content of this paper provides new research methods for the characteristics and prevention of "spraying",the improvement mechanism of soil conditioner,and the migration law of soil in screw conveyors.It has important reference significance for EPB shield tunneling through water-rich sandy layer.