Study On Influence Mechanism Of Grouting Pressure On Existing Shield Tunnel Structure

As an important form of urban rail transit,subway can not be ignored for its own safety and stability while greatly facilitating people’s travel.Especially in the subway tunnel with relatively developed underground water system,the water rich surrounding rock will pose a potential threat to its safety,which is easy to cause water leakage,water inrush and even water inrush accidents in subway tunnel.At present,grouting is commonly used to solve such problems to reduce the permeability of the rock and soil near the tunnel lining,blocking the water passage between groundwater and the tunnel chamber.At this time,the control of grouting pressure is crucial:excessive grouting pressure can damage the tunnel structure and even cause safety accidents,and too small pressure can make the slurry unable to effectively fill the gaps,failing to achieve the expected water blocking effect.This article is based on the ground grouting project at the Lashan Station of Jinan Metro Line 2.Through theoretical research,laboratory tests,numerical analysis,and on-site tests and applications,the influencing factors of grouting pressure transmission and the mechanism of action on the existing tunnel structure are studied.The main research content and achievements are as follows:(1)According to the stress state of soil around the tunnel,a generalized model of tunnel stress under grouting pressure is established.Based on the viscosity time-varying characteristics of Bingham fluid and the tortuosity theory of diffusion path,the pressure distribution formula of slurry seepage diffusion mechanical model is derived,and the calculation method of segment load under grouting pressure is obtained.The influence of viscosity time-varying and diffusion tortuosity on seepage effect is analyzed according to the project case.(2)A shield tunnel model test system was independently developed based on the study of sand layer grouting reinforcement of tunnels.Mechanical response model tests of shield tunnels under grouting pressure were conducted to study the stress,strain,and displacement responses of shield tunnels under different grouting pressures.By analyzing the mechanical response monitoring data of the tunnel model,the influence of grouting pressure on the existing shield tunnel structure was obtained.(3)Based on the relevant equations of solid mechanics and the physical field of Darcy’s law,the finite element software COMSOL Multiphysics was used to simulate the seepage and diffusion process of grout in the sand layer under the tunnel environment.The influence process of grouting pressure conduction on the strain and displacement of the tunnel wall was restored,and the mechanical response law of grouting pressure on the existing shield tunnel segments was obtained.Through mutual verification with model tests,its rationality and accuracy were proved.(4)Based on the ground grouting project at the Lashan Station of Jinan Metro Line 2,onsite engineering experiments were conducted to determine the range of grouting pressure based on relevant theoretical experimental research,deepening the application of theoretical research to practical engineering projects.Through real-time monitoring of the on-site tunnel,the changes in tunnel stress,strain,and displacement under the influence of parameters such as grouting pressure,grouting distance,grouting time,and grouting frequency during the actual construction process were analyzed,Further optimize and adjust the grouting plan based on information technology.(5)The above research content has been successfully applied to the subsequent ground grouting project at Lashan Station of Jinan Metro Line 2.During the treatment process,the grouting pressure was scientifically and reasonably controlled.After testing,good grouting effect was achieved,ensuring the stability of the tunnel and surrounding soil,and the pump room and water tank inside the tunnel were restored in a safe and waterless state,providing strong guarantees for the long-term safe operation of the Lashan section of Metro Line 2,It has important guidance and reference significance for similar projects.