Study On Impact Of Big Gradient And Curve In Small Radius On The Stability Of Shield Tunneling Excavation Face And The Stress Of Segment

ABSTRACT:To better meet the needs of network planning, project construction and operation, the liner motor traction transportation system is first adopted in Guangzhou City of China. Compared with the traditional traction transportation system, the linear motor-driven subway system has an excellent dynamic performance and grade ability, which means the greatest gradient of line can reach 80‰and the minimum radius can be reduced to 80m. Although the linear motor-driven subway system has a lot of advantages such as flexible election of line, reducing depth of tunnel, lowering project cost.etc, it also brought some new challenges and problems for its running tunnel construction, such as the stability of excavation face, the increasing gap of shield tail, and so on.This paper has a study and discussion on problems related with the Impact of Big gradient and curve in small radius on the stability of shield tunneling excavation face and the stress of segment through theoretical analysis, numerical calculation, on-site measure and comparative analysis, and so on, which takes Guangzhou Metro Line 4 and 5 with large gradient and curve in small radius shield tunnel project as background, aiming at distinct features of the linear motor-driven tunnel with large gradient and curve in small radius.(1) Based on the limit equilibrium theory, longitudinal gradient,and introducing the lagrange multipliers, the problem of soil pressure is described as calculus of variations view, which converts the functional extreme value problem of passive and active earth pressure into the extreme issues of general function through the limit equilibrium variation law and the geometric relations of solving problem. It makes a study of the calculation problems of the limit active earth pressure and limit passive earth pressure on the soil of the shield tunneling excavation face, analyzes the impact of soil parameters surrounding tunnels on the support pressure of the excavation face, discusses the position change of action point of support pressure under different conditions, and further explores the impact of the prop-setting grade construction method against to limit support pressure on excavation face.(2) By means of numerical simulation method, and in light of the actual on-site construction, the variation laws of stress and displacement of excavation face and surrounding stratums in shield tunneling under the condition of large gradient are studied in this paper, which analyzes the impact of the size of longitudinal slope on the displacement of surrounding stratums in different direction, convergence displacement, principle stress around excavation face, plastic zone,etc, and further explores the impact of pressure of the soil chamber and grouting effect in shield tail on the situation of stratums deformation and stress.(3) By ANSYS and FLAC3D joint modeling and calculating, this paper is to study the variation laws of stress and deformation of surrounding stratums induced by shield tunneling construction under the condition of curve in small radius, and to analyzes the impact of curve radius, asymmetrical thrust, grouting effect in shield tail on the construction of shield tunneling with small radius. At the same time, how to calculate the gap of shield tail in curve tunnel is discussed and the reliability of its result can be ensured by the asymmetrical thrust which is accordance with the construction site statistics.(4) By the stratum--structural calculation mode, the mechanic characteristics of shield tunneling segment lining under the condition of curve in small radius are studied in this paper, as well as the impact of curve radius, grouting method, size of longitudinal slope,etc. on the stress state of segment.(5) Based on the components of shield tunneling machine used in curved segment and the characteristics of tunneling construction, this paper is to discuss the axis controlling technologies under the conditions of small radius and overall lateral tilt during tunnel construction, and it points out that the reasonable thrust and driving speed are important elements to guarantee construction safety in shield tunneling. Finally,it is tested and verified through case study that it is safe to carry on shield tunneling under the conditions of small radius.