Numerical Simulation Measured Analysis Of Freezing Reinforcement For Cross Passage Of Shield Metro Tunnel

As one of the subway construction methods,freezing method is widely used in the construction of shield subway tunnel cross passage because it can effectively isolate the groundwater and strengthen the soil.The previous freezing design experience mainly comes from the mine,which basically adopts the way of vertical or horizontal freezing.And shield the freezing method construction of cross passage in metro tunnel,due to the influence of the tunnel space,frozen pipe usually in radial arrangement,but the current subway connecting passage on analysis of the temperature field of the frozen wall are simplified as frozen pipe horizontal layout,frozen wall equivalent body heat source instead of freezing pipe heat source and plane problem,difficult to real representation of the arbitrary point and the temperature in the actual engineering situation.At the same time,the research on the stability of frozen soil curtain excavation is usually carried out with a plane problem or a simplified three-dimensional model,which will also lead to differences with the actual situation.Based on the above problems,this paper analyzes the measured data during the active freezing period and the excavation construction stage of the freezing reinforcement of the cross passage,taking the freezing method construction of the cross passage between XIAOMAZHUANG Station and GAOLOUJIN Station of the east extension of Beijing Metro Line 7 as the background.And according to the construction site in geotechnical engineering exploration report,the freezing wall design,the measured data of construction materials,FLAC 3D numerical simulation software was used to study the influence of temperature field variation,mechanical properties of freezing wall and soil parameters on freezing reinforcement behavior of cross passage.It is expected to provide reference for the design and construction of the freezing method of contact passage in the future.The main research contents and conclusions of this paper are as follows:(1)Case analysis of freezing reinforcement of cross passageAccording to the freezing reinforcement example of the connection channel,the measured data of frozen salt water temperature,frozen soil temperature and pressure relief hole are analyzed,and their respective variation rules are obtained.Based on the monitoring data,it is determined that the frozen wall had met the excavation requirements when the active freezing lasted for 35 days.According to the feedback of the frozen wall information during the excavation stage,the accuracy of the results obtained from the monitoring data analysis during the active freezing period is confirmed,and the rationality of the freezing design parameters is also reflected.(2)Numerical simulation and analysis of three-dimensional freezing temperature field of cross passage.Using the FLAC 3D thermal analysis module,according to the geotechnical engineering survey report of the construction site and the measured temperature of the saline water in the freezing pipe during the active freezing period,the three-dimensional freezing temperature field model of the contact channel is established,and the variation rule of the freezing temperature field and the time point when the cross ring and thickness of the freezing wall reached the designed value are obtained.The numerical results show that the time required for the frozen wall to reach the design value is 30 days,while the time determined by the measured data is 35 days,which is basically close to the two.At the same time,the temperature data calculated by numerical method is compared with the measured data,and the two are basically consistent,which verifies the accuracy of the model.It shows that the numerical simulation results of freezing temperature field can provide reference for practical engineering.(3)Numerical simulation analysis of excavation stability of frozen wall of cross passageIn order to better reflect the stress and displacement of the frozen wall,when using FLAC3 D calculation to take the most unfavorable conditions,namely,do not use any supporting the whole construction process simulation.Based on the bearing capacity of the frozen wall itself,the stress field and displacement field of the frozen wall in the three different construction stages of segment breaking,tunnel excavation and pump house excavation are comprehensively analyzed,and the distribution characteristics of the stress and displacement field are obtained,and relevant suggestions are put forward to ensure the construction safety.(4)Analysis of influence of soil parameters on freezing reinforcement behaviorUnder the condition of ensuring the accuracy of the model,the influence of different soil parameters on freezing reinforcement behavior was studied.The first is to study the influence of soil parameters on the temperature field model,and obtain the influence law of thermal conductivity coefficient,specific heat capacity,density,minimum brine temperature and formation temperature on the temperature field.2 it is to study the effect of soil parameters on the mechanical model,it is concluded that freezing wall elastic modulus,thickness of frozen wall,fluid-structure interaction effect on the influence law of stress field,displacement field,the fluid-structure coupling effect is the most significant influence on the stress field,displacement field,in the underwater tunnel frozen wall design,water seepage effects cannot be ignored.