Field Test And Numerical Analysis Of Mechanical Behavior Of Advanced Small Pipe In Sandy Soil Area

With the rapid development of the city,to alleviate the urban traffic pressure on the ground,the city subway come application,and the shallow depth in the urban subway excavation method of step-by-step excavation is a more commonly used method,the preliminary support of the excavation of the method is particularly important,advanced small pipe grouting support with the preliminary support of the safety performance is high,the effect is obvious,and the advantages of simple transfigure and sensitive operation is widely used.The excavation of the tunnel with a small distance in urban subway will have a negative impact on the existing pipeline and the surface.Through literature and actual investigation,relying on the project of zhengzhou subway line 4,the finite element software simulation and theoretical analysis,field test and indoor parameters determination test,the method of combining the sandy region of urban subway shallow tunnel excavation method of step-by-step excavation of leading ductule pre-reinforcement mechanism were studied.By referring to the literatures,it is found that the role and effect of pre-reinforcement of strata leading small ducts are also different in different areas.By combining the research thought of this paper with practical engineering,some theoretical and practical research results have been obtained.The main research content of this paper is as follows:(1)Literature review was conducted to summarize the advantages and disadvantages of several advanced tunnel precast support methods,and the domestic and foreign researches were summarized from the aspects of tunnel deformation and stability studies,field engineering examples,model tests and numerical simulation.(2)Using the project of shangdu road station of zhengzhou metro line 4 for half a year,the response law of strata,the essential characteristics of strata response and the distribution law of surrounding rock pressure under the three conditions of tunnel face passing before,during and after excavation are obtained.(3)This paper introduces the advance in the process of tunnel excavation pre-reinforcement mechanism of small tube,the catheter after grouting reinforcement stress characteristics of surrounding rock,in the process of predecessors' research on the excavation of tunnel stability evaluation method is put forward on the basis of a new idea of evaluation method,and the advanced small duct grouting of surrounding rock after theory analysis,it is concluded that the excavation surrounding rock elastic-plastic change rule,in the process of surrounding rock stress and displacement after reinforcement is given the formula of quantitative analysis.(4)Based on Winkler foundation model,the settlement of ground surface in office a bit and that point is directly proportional to the pressure of the per unit area,to establish the model of the stability of the overlying soil tunnel,and according to the model structure of overlying soil Ren Yiwei unit in mechanical equilibrium analysis,to maintain the stability of the tunnel in overlying soil is deduced the calculation formula of horizontal thrust.Based on this theory,the mechanical model of the pipe in the excavation process is established,and the force of the model is analyzed to obtain the deflection,bending moment and turning Angle of any point of the pipe.(5)By establishing the verification of mechanical behavior model of strata pre-reinforcement and the numerical simulation of Abaqus finite element software,the effect of pre-support of small lead pipe was obtained,and the parameters and support mode of small lead pipe were optimized.