Study On Penetration And Reinforcement Mechanism Of Grouting In Sand Layer Disclosed By Subway Tunnel And Its Application

With the development of China's subway entering large-scale construction period,controlling of disaster due to bad geological condition has become an important research topic.Subway tunnel often pass through the grade IV water-rich sand layer,which is one of the major sources of geological hazards affecting the safety of the subway construction.The characteristics of this stratum is of rich water,low bonding strength,and poor self-stabilizing ability,thus tunnel collapse,inrush of water and sand,and other engineering disasters could be caused by construction disturbance and groundwater pressure.Grouting is the most common method used to control the geological disasters related to water-rich sand layer.Under the influence of pore structure and in-situ stress of sand layer,the sand grouting tends to present different modes of diffusion and reinforcement.In the present thesis.two most common modes of sand grouting in engineering project were considered,including penetration grouting and fracturing-compaction.Aiming at quantitatively describing the process of grout penetration and grouting effect,and investigating the mechanism of grout penetration and reinforcement in depth,a quantitative method was established to calculate the penetration range of grout and the effect of grouting reinforcement,based on theoretical analysis,lab test,and simulation experiment.Finally,a method aiming at sand grouting designing was developed and used in engineering application.The main content and breakthrough of the present thesis are as follows:(1)The diffusion and reinforcement of sand grouting is subject to the penetrability of sand layer and the level of grouting pressure.Based on the penetrability test on grouting of sand layer,the criterion was developed for determining the penetrability based on the corresponding sand layer structure and the slurry size of cement grout used.Based on the radial grout penetration,the criterion was established for determining the initiation of fracture grouting.Therefore,the occurrence condition of penetration grouting and fracture-compaction grouting were presented,respectively.(2)Considering the influence of different grouting methods on the spatial distribution of slurry viscosity,the theoretical model of sand penetration grouting considering the inhomogeneous spatial distribution of viscosity was established,and a one-dimensional visible simulation experiment was conducted.Comparison between grouting theory and experimental results lead to the quantitative relationship between the range of grout penetration and grouting parameter,rheological properties of cement grout(3)Lab experiment on the reinforcement effect sand grouting was carried out,to study the influence of of slurry properties,sand layer characteristics and grouting pressure on the grouting effect.It was found that the water-cement ratio was the governing factor affecting the grouting effect,and the grouted samples corresponding to different water-cement ratio present different failure mode.The quantitative relationship between the effect of the grouting reinforcement and the relevant water-cement ratio and the curing time was obtained by fitting the test data.(4)The compaction properties of sandy clay under different soil content and water content were studied based on lateral compression test,and a mathematical model was developed to describe the nonlinear compaction process of sand layer.Moreover,a theoretical model for considering the coupling of grout flow field and the relevant stress field of sand layer was established,and an algorithm is proposed to the dynamic development of fracture channel,thus,making it possible to describe the whole process of fracture-compaction grouting,and time and spatial distribution of channel aperture during the corresponding process of grout penetration.(5)The quantitative relationship between the grouting effect of compacted sand layer and the relevant pressure applied was obtained through a series of mechanical tests,and the quantitative relationship between the performance of grouted sand and the water-cement ratio and curing period was obtained.A simplified physical model was built to describe the overall performance of the grouted sand layer,and the quantitative estimation of the reinforcement effect of fracture and compaction grouting,with comprehensive consideration of the contribution of the grout skeleton formed during grout penetration and the compacted sand layer to the overall performance of the grouted sand layer.Thus,the anisotropy and spatial distribution of grouted sand layer were obtained,and the influence of grouting pressure,the grout take of single hole,the spacing of grouting hole,and compaction characteristics of sand layer on the grouting reinforcement effect of fracture-compaction grouting were systematically analyzed.(6)Visible grouting simulation test system was designed and developed,making it possible for visible simulation of the fracture-compaction grouting process.The characteristics of the dynamic evolution of the stress and displacement field of sand layer,and the propagation of fracture channel were derived.Through comparison with the relevant reinforcement theory,the inner mechanism was further revealed.(7)Based on the research results of the grout penetration and reinforcement mechanism of sand grouting,a grouting design method for sand layer was put proposed.The research results were successfully applied to the grouting reinforcement project for Qingdao Metro Line 2 within Bai-Miao water rich sand layer,and the grouting effect was fairly good.Therefore,the current method proposed is of a broad application prospects.