Study On The Mechanical Behavior Of Large-section CRD Method Of Sand-viscosity Composite Formation

In recent years,the scale of subway construction in major cities in China has been expanding,and at the same time,the design and construction of large-section tunnels such as subway crossing lines and parking lines under complex geological conditions have also increased,bringing new challenges to design and construction.Moreover,due to the influence of many factors such as geological conditions and construction conditions,the stress state of the tunnel support structure obtained only by numerical simulation and theoretical analysis is difficult to reflect the actual situation,and it is impossible to provide a sufficient basis for the design and construction of tunnels under complex geological conditions.However,with the rapid development and wide application of on-site real-time monitoring equipment and technology,on-site monitoring has become an important means to analyze and evaluate the rationality and safety of support structures.Especially in the special section with poor surrounding rock conditions,the comprehensive on-site measurement data analysis of the mechanical properties of the tunnel in the early stage is of great significance for the design and construction of the tunnel.The excavation of water-rich sand-stick composite strata can easily induce complex problems such as excessive deformation of the surface and supporting structures.In this paper,based on the tunnel project of the underground excavation section between Panjiayuan Station and Guangqumenwai Station of Beijing Metro Line 17,comprehensively using the analysis methods of on-site monitoring and numerical simulation,an in-depth analysis of the underground excavation of the subway under the water-rich sand-stick composite stratum is carried out.The main research work and research results of the mechanical behavior of tunnel construction are as follows:(1)During the construction process,the surface subsidence,vault subsidence,pore water pressure,surrounding rock pressure,initial support internal force,etc.were monitored on site,and the change law and overall distribution of each monitoring object were summarized and obtained.It provides monitoring data support for the initial support design and construction of large-section underground tunnels under this type of water-rich sand-stick composite stratum.(2)The whole construction process is analyzed in detail through the numerical model after checking the field measured data,and the influence of different construction methods and dismantling lengths on the deformation in the subsequent secondary lining construction stage is studied.Reasonable suggestions are put forward for the dismantling plan and the length of single dismantling during the subsequent secondary lining construction.(3)The key influencing parameters in the construction process of the undercut tunnel are selected,the influence of different parameter values on the deformation and stress of the undercut tunnel is analyzed,and relevant suggestions are put forward.The analysis shows that the grouting effect of the 3 sides of the pilot tunnel is very important to control the settlement and deformation of the tunnel construction,so the grouting effect of the 3 sides of the pilot tunnel should be strictly guaranteed during the grouting process;When the clear distance between two parallel tunnels is greater than 2 times the diameter of the larger section,the mutual influence between the tunnels may not be considered;Before design and construction,the constraints in the construction process should be fully considered,and a reasonable construction organization plan should be arranged according to the actual situation on the site to ensure that the misalignment of each pilot hole is basically kept within a small range during construction.