Study On Drainage And Depressurization Technology Of Tunnel In Water-rich And Strongly Sandified Dolomite Stratum

Dolomite sandification is a long-term homogeneous dissolution of geological processes.The solubility of dolomite is lower than that of limestone,and it is difficult to form large-scale karst cavities or karst pipelines.Therefore,engineering research often ignores its hazards.After strong sanding,the dolomite becomes loose and porous,and the tunnel construction is prone to collapse of the vault and sudden surge of the face.Burst is a difficult problem in tunnel construction,and the current research on tunnel burst is mostly the treatment after burst.Although the tunnel drainage and pressure reduction is an effective surge prevention method,there are few research results on its specific prevention and control effect.Based on the Jixin Tunnel of Chengdu-Kunming Railway,this paper studies the engineering characteristics of dolomite before and after sanding by literature analysis and laboratory test.According to the on-site burst situation,the burst mechanism of tunnel in water-rich and strongly sandified dolomite stratum was analyzed.Various methods such as theoretical derivation,model test and numerical simulation are used to study the key technologies of advanced drainage pipe and radial drainage hole of water-rich sandy dolomite tunnel.The research results are expected to provide new ideas for the design and theoretical research of tunnel construction dewatering in water-rich broken and loose surrounding rock.The main contents of this paper are as follows:(1)Starting from the nature of sandified dolomite,the characteristics of sandified dolomite are analyzed.Considering the factors such as the sanding ratio of the tunnel face,the seepage of the tunnel face,the stability of the tunnel face and the deformation of the tunnel,the sandified dolomite is reclassified.The physical and mechanical properties of dolomite and strongly sanded dolomite were measured,including the uniaxial and triaxial compressive strength of dolomite,the density,water content,gradation,permeability,cohesion,internal friction angle and elastic modulus of strong sandified dolomite.(2)It reveals the multiple water and sand inrush and disposal methods of No.1 horizontal tunnel,No.2 horizontal tunnel and main tunnel of Jixin tunnel,and summarizes its inrush characteristics.The dynamic analysis of the water inrush process of Jixin tunnel is carried out,the disaster-pregnancy mode of the inrush in the strong sandification section is analyzed,the development mechanism of the disaster source and the inrush channel inrush process are described,and the inrush mechanism of the sandy dolomite tunnel is summarized.(3)Through the similar model test of fluid-solid coupling,it is intuitive to explore whether the advanced drainage pipe plays a role in drainage and pressure relief and maintaining the stability of the tunnel face.Then through numerical simulation combined with formula derivation,the applicability of the advanced drainage pipe is analyzed with the groundwater level and the length of the advanced drainage pipe as variables.This process takes into account the deformation of the surrounding rock ahead of the face,the longitudinal section shape of the pressure arch ahead of the face,the stability of the face(virtual support force)and the pore water pressure of the formation after drainage.(4)Using numerical simulation method,the length of drainage hole,radial drilling position,transverse inclination angle,circumferential spacing,longitudinal spacing and longitudinal inclination angle are calculated variables.The influence of various factors on lining water pressure,lining deformation and shotcrete stress is studied by control variable method.Finally,the construction parameters of radial drain hole around the tunnel suitable for water-rich and strongly sandified dolomite tunnel are proposed.