Analysis Of Positive And Negative Problems Of Water Gushing And Protection During Tunnel Excavation

With the continuous development of China 's economy,the people 's demand for transportation has become more and more intense.Compared with socio-economic development,transportation development has achieved a historic change from “bottle-back constraints” to “basic adaptation” in economic development.The transportation powerhouse has laid a solid foundation.Tunnel engineering is an indispensable item in the transportation industry.Up to now,the total length of tunnels in China has reached 15,285 kilometers,and the total number of tunnels has reached 16,229.China has the largest number of tunnels in the world.However,in the process of tunnel construction,tunnel seepage and water gushing have always been recognized as problems that plague tunnel design,construction,operation and management.Tunnel seepage or water gushing problems account for more than 80% of common tunnel diseases.The use of appropriate and diversified design methods to solve the problems of tunnel support and tunnel gushing can not only maintain the coordination between people and the natural environment,but also ensure the personal safety of tunnel users,maintain social stability,and promote harmonious social development.The purpose of this paper is to take the topic of gushing water and protection during tunnel excavation,take the boundary element method parameter inversion technology as an example,take the Jigongshan Tunnel as an example,and combine the local tensile fracture based on the M-C criterion to destroy surrounding rocks The safety factor is the strength reduction method of the criterion,and the forward and reverse analysis and optimization methods of the surrounding rock supporting structure of the gushing tunnel are established.(1)Based on the problem of small holes in an infinite plane,a boundary element inversion method for the surrounding rock parameters of a tunnel is established by the imaginary stress method in the boundary element.Based on the analytical solution of the displacement of a circular tunnel with uniform isotropy,the parameter identification condition is introduced to verify the uniqueness of the inversion parameter,and the parameters to be inverted in this paper are the elastic modulus and side pressure coefficient;(2)According to the principle of maximum displacement,the optimal measurement content of the tunnel is determined as the amount of sinking of the vault and the amount of convergence of the headroom.By analyzing the displacement monitoring data of Jigongshan Tunnel,the elastic modulus of section YK133 + 270 of Jigongshan Tunnel is 10.37 GPa and the side pressure coefficient is 0.48.The cross section YK133 + 290 with similar geological conditions in YK133 + 270 section was selected for simulation.The degree of coincidence between the calculated displacement and the measured value at the same survey line of the section was compared.The relative error between the two was 6.75%,indicating that Rock displacement back analysis results are reliable;(3)The excavation model of Jigongshan Tunnel was established to simulate and analyze the phenomenon of water inflow during tunnel excavation.Perturbed by tunnel excavation,the water storage characteristics and seepage characteristics of fractured rock masses are changed,and it is concluded that fracture penetration is a sufficient condition for tunnel seepage to be transformed into tunnel gushing water.Combined with water supply conditions such as atmospheric precipitation in the Jigongshan Tunnel,determine the waterproof method of grouting and laying waterproof layer and "Drainage Ditch under the Yanggong" to prevent water inrush in the Jigongshan Tunnel;(4)Based on the M——C criterion,the safety factor of the local rock fracture in the surrounding rock is used as a criterion to design and simulate 6 tunnel supporting structure schemes,and calculate the strength reduction method.Considering the four factors of the safety factor of the tunnel supporting structure,the settlement of the tunnel vault,the amount of bulge at the bottom of the tunnel,and economic factors,the optimal supporting scheme for the Jigongshan Tunnel is determined as follows: 6 bolts at the waist,vault There are 12 anchors,the bottom lining thickness is 60 cm,and the waist and vault lining thickness is 45 cm.