| Since the 20 th century,China’s urban construction has entered a high-speed development stage,but due to the limited urban land resources,the development of underground space has become an inevitable trend of future urban development.As a fast passage of the city,subway has been operated in developed countries as early as last century.With the increasing pursuit of living standards in China,subway construction has become an important guarantee for the development of domestic cities.In Urumqi Metro Line 1 project,a large number of pebble stratum formed by accumulation of riverbed is distributed along the line.Due to the characteristics of small cohesion and large dispersion of pebble stratum,many technical difficulties are brought to the construction of the project.In this paper,combined with the needs of the project construction,the mechanical response of the excavation of pebble stratum tunnel is studied,and the adaptability of the excavation method of pebble stratum tunnel is discussed.The specific research contents as follows:(1)Combined with the physical properties of pebble stratum,the reasons for choosing discrete element method are described.Then,the numerical triaxial model is established by PFC3 D particle flow software,and the triaxial test results under different micro parameters are obtained by servo mechanism control.Then,the micro parameters such as density,porosity,indirect contact stiffness of particles,friction coefficient and so on are studied respectively The influence law of sex;(2)Through PFC2 D particle flow software,the excavation model of pebble stratum under self weight stress is established,and the deformation law of deep tunnel and shallow tunnel and the stress development law of surrounding rock are studied respectively.Then,through the establishment of a variety of working conditions simulation,the influencing factors of deformation law are analyzed;(3)Through the discrete element numerical model,three construction methods are used to simulate the excavation of pebble stratum,and the dynamic mechanical response process is analyzed;(4)According to the principle of similarity ratio and the actual geological conditions,the similarity ratio of the model is 1:20,and the similarity relationship between the model parameters and the prototype is deduced by combining the dimensional analysis method,and the mixture ratio of similar materials is determined by direct shear test according to the orthogonal test scheme.(5)Through the establishment of pebble stratum excavation model test platform,the model excavation test of pebble stratum under multiple working conditions is carried out,and the development law of stress and deformation of pebble stratum in numerical simulation is verified. |
