Studies On The Mechanism And Engineering Application For The Remediation Of Existing Shield Tunnel Using Grouting Technique

In recent years,underground construction near existing shield tunnel has become an important factor affecting the tunnel structural safety.For the shield tunnels affected by the surrounding construction works,a series of structural diseases can be caused by large tunnel displacement,such as joint opening,lining cracks,seepage and track bed defects.The"Double-liquid Micro-perturbation Grouting Method" is an effective way for correcting the excessive tunnel displacement.This method uses sleeve pipe grouting technique and grout mixed by cement and sodium silicate.In this paper,systematic research was carried out to study the mechanism of remediation for displaced shield tunnel using grouting technique.The main achievements are as follows:(1)Based on the smeared crack model and Volume of Fluid method,the diffusion mechanism of cement grout in completely weathered granite was studied by finite elment analysis.The results show that the main types of grout veins are "linear shape","T shape" and"trigeminal shape".With the increase of grout viscosity and injection rate,the width of grout veins and the final grouting pressure increase gradually.The depth of soil sample and the permeability of model boundary also have important effects on the shape of grout veins and final grouting pressure.(2)On the basis of the theory in the previous chapter and Bingham fluid constitutive equation,the fracture mechanism of cement-sodium silicate grout in completely weathered granite was studied by finite element analysis.The results show that the fracture patterns are"linear shape","trigeminal shape" and "dispersive shape".When the water cement ratio is large,"Dispersive shape" occurs,and the main flow direction of the grout transits from the main grout vein to the secondary grout vein.Forks can be found in the secondary grout vein.Water cement ratio,grouting flow rate and soil depth are main factors affecting the fracturing process of grout mixed by cement and sodium silicate.(3)Model test on the remediation of shield tunnels using grouting technique was carried out by self-developed equipment.Combined with finite element analysis,the development of stress and deformation of tunnel structure under different grouting parameters was studied.The results show that grouting under the side of the tunnel can could both horizontal and vertical displacements of the existing tunnel.The horizontal diameter of the central section decreased while the vertical diameter increased.With the increase of grouting pressure,height and buried depth of grouting zones,also with the decrease of soil modulus,the horizontal and vertical displacements at the tunnel axis gradually increase,and the deformation degree of section increases.(4)Based on the remediation project of a displaced shield tunnel in Shenzhen,field measurement research was carried out.The safety of tunnel structure during the grouting process was evaluated by different serviceability indexes.The results show that"Double-liquid Micro-perturbation Grouting Method" was effective in reducing the excessive displacement of shield tunnel.The deformation of typical tunnel section was composed of translation and shape change.After grouting,the horizontal displacement,settlement,horizontal convergence and ellipticity of the shield tunnel decreased.The serviceability of the shield tunnel was improved and remained stable.(5)A finite element analysis method considering the grouting construction sequence was proposed.The whole grouting process was divided into several stages.At each stage,the grouting process in different soil layers was simulated by applying expansion force and controlling volume expansion rate in the reinforcement area.The soil parameters of the grouting zones were enhanced after the grouting process.According to the remediation project in Shenzhen,a three-dimensional finite element model was established.The rationality of the finite element method was proved by comparing the simulated tunnel displacement with the measured tunnel displacement.This method can be applied in the design of similar remediation projects to help improve the grouting efficiency and ensure the structural safety of shield tunnel.