Research On The Division Method And Tunneling Parameter Control Of Shield Tunnel Construction In Composite Strata

In recent years,the scale of China's transportation engineering construction has shown a trend of rapid growth,especially in the urban transportation construction has gradually formed a city traffic system with underground railway traffic as the main traffic,and multiple rail transit coexist.Shield tunneling method has been widely used in subway construction in China due to its advantages of low noise and fast speed.However,in the process of building complex of shield tunnel construction environment,excavation face and rear most of the space occupied by a large shield,lead to some efficient,fast advance geological prediction technologies(such as the transient electromagnetic method,TSP,etc.)it is difficult to carry out in the shield tunnel,the geological exploration of unclear tend to induce shield machinesuch as landslides,gushing water sand construction accident,in addition,there are part of the construction accident is due to the construction of shield construction parameter Settings,error,etc.Not only caused casualties and equipment damage and other major accidents,but also to the country caused huge economic losses.Therefore,it is of great significance for the safety and efficiency of shield tunneling construction to seek a method that can not only include the physical and mechanical properties of surrounding rocks,but also consider the construction environmental risks.On this basis,the corresponding relationship between tunneling parameters and construction sections is established.This study takes Chengdu metro line 18 as the engineering background,and adopts the method of combining theoretical analysis,numerical simulation and field application to analyze and study shield tunneling under the condition of composi te strata.The main conclusions are as follows:1.On the basis of the existing stability coefficient method,the value range of the stability coefficient of shield tunneling face under the condition of composite strata is proposed and verified by the finite element method.The research results show that:(1)under different burial depths,the value range of excavation surface stability coefficient is roughly the same.When 2?N<6,the excavation surface is in the elastic deformation stage.When 6?N<8,the excavation surface is in the plastic deformation stage;When N?8,the excavation face becomes unstable and fails;(2)Under the condition of composite stratum,the stability coefficient should be controlled within the range of less than 6 and no more than 8.The construction sections are divided into 4 categories and 12 subcategories;2.To achieve the refinement of the construction group section division method operation,improve the understanding of GPR image characteristics,improve the interpretation precision of ground penetrating radar(GPR),using the finite difference time domain method(FDTD)elaborating on underground pipeline detection,including the geological interface,pipeline buried depth,filling material,the line,the numerical simulation of the influence factors,such as pipeline disease synthesis gallery forward modeling based on this,instruct the practical detection of ground penetrating radar(GPR)images of interpretation work.The results show that:(1)with the increase of the buried depth of the target body,the electromagnetic energy is gradually absorbed by the surrounding rock-soil body,and the reflected signal of the target body is weakened;(2)the greater the difference in the relative dielectric constant between the target and surrounding rock and soil,the stronger the reflected signal will be;Conversely,the weaker the reflection signal;(3)water has a great influence on the propagation of electromagnetic wave,and the presence of water will cause multiple waves to form below the target body;3.Group division method,based on the construction by establishing the mathematical physics models,unearthed pressure balanced shield tunneling is derived the mechanical equilibrium equation and equilibrium equation of continuity,get the earth pressure balance shield owe propulsion,earth pressure balance and advance three kinds of condition of total balance equation,reveals the essential between the parameters of mathematical physics,and with the background of Chengdu metro line 18,puts forward the value range of each parameter and to guide the construction.