Study On Influencing Factors Of Curtaingrouting In Dolomite Sandifaction Zone

With the vigorous development of China transportation infrastructure,the proportion of tunnel construction in traffic construction is increasing and the importance is getting higher and higher.Nowadays,tunnels have become a control project for an engineering project.However,as more and more tunnels are built,the unfavorable geological conditions encountered during the construction process are also increasing.Relevant research on the application of bad geology and related technologies encountered in tunnel engineering in bad geology can provide corresponding guidance and reference for future construction and design,and provide guarantee for safe construction,so it is necessary.Based on the Jinyunshan tunnel of the suburban railway（orbital extension line）to the Bishan section of the Chongqing suburban railway（orbital extension line）,this paper studies the related problems of curtain grouting engineering in the sand-filled dolomite tunnel,and has carried out the following aspects.jobs:1)Two necessary preconditions for the dolomite sandification are analyzed:（1）there is water flowing through the rock mass;（2）the rock mass is soluble and has its own crack.The dolomite will have obvious stratification due to the different degrees of sandification.From top to bottom,it is the upper silty clay,the middle layer of dolomite sand and the lower layer of dolomite sand.In the process of sandification of dolomite,the content is the most.The CaO and MgO decreased gradually,and the SiO₂ content increased gradually.Al₂O₃ and Fe₂O₂ formed a secondary clay mineral by precipitation with SiO₂.The accumulation or dissolution process of various elements showed a certain correlation with the dolomite sanding and dissolution process.2)A comprehensive analysis of several major factors affecting curtain grouting is mainly analyzed from the aspects of grouting pressure,material selection,slurry ratio and grouting thickness.The calculation method and empirical formula of grouting pressure are given.The way of boosting during grouting is analyzed:one boost and one step boost,and the applicable conditions are respectively explained.Three different comparisons are analyzed.Grouting materials（single liquid cement slurry,double liquid slurry,superfine cement）applicable engineering conditions,and common material ratios;three different grouting reinforcement ring thickness calculation formulas are given,and theoretical formulas and experience are used.The formula calculates the thickness of the curtain grouting reinforcement ring of the Jinyunshan tunnel,and concludes that the optimum grouting ring thickness is 6m.3)Using the ansys modeling analysis,a three-dimensional model of surrounding rock reinforcement by three grouting materials was established.By analyzing the calculation results of the three models,it was concluded that the double liquid slurry is the most suitable for the curtain grouting project of the karst belt in the Jinyunshan tunnel.Slurry material;established a two-dimensional model that can change the thickness of the grouting reinforcement ring.By changing the thickness of the reinforcement ring to record the change of the force of the lining structure,it is found that the thickness of the reinforcement ring has a certain effect on improving the structural stress,but the effect is not large,combined In the previous conclusion,the relationship between the thickness of the reinforcing ring and the seepage prevention water can be concluded that the thickness of the grouting reinforcement ring has a greater effect on the seepage prevention water,and the effect of improving the structural stress is not obvious.4)The construction scheme and process of the advanced curtain grouting project in the geological section of the Jinyunshan tunnel are described.The material selection,parameter design,process and grouting results are introduced in detail,and the curtains of the Jinyunshan tunnel are summarized.It all comes down to this:（1）The key factors of curtain grouting are grouting pressure,grouting material and curtain thickness in sanded dolomite silt fine sand layer;（2）The high pressure splitting grouting should be used in the filling cavity of dolomite sanded section silt fine sand,and the final grouting pressure should be 3⁵ Mpa,which can be determined by experiment in practice.The superfine grouting material is used as far as possible to reinforce the tunnel to form a consolidated curtain with high strength,early strength,uniformity and good continuity,effectively blocking the underground water passage and squeezing the water in the tunnel excavation area as far as possible.Pore-forming technology is also the main problem that restricts the quality of grouting.Progressive grouting technology can better solve the problem of hole-forming quality,but the length of segments should be adjusted reasonably according to the site conditions.Progressive sectional grouting technology should be adopted for dolomite sanding section,and the length of segments should be 0.5¹m.（3）Because of the heterogeneity of strata,there are great differences in grouting capacity of strata.If superfine cement is used in strata with large grouting volume,it will inevitably increase investment and waste resources.Therefore,in grouting process,appropriate grouting materials should be selected according to specific conditions to ensure the social and economic benefits of construction.In specific projects,double grouting can be carried out first.Maintenance circle is formed by grouting,and local reinforcement of superfine cement is carried out.（4）The grouting thickness formula can be calculated by empirical formula,which is convenient and simple,and the excavation radius value can be obtained in general stratum.The experience and lessons of the pulp engineering,and suggestions on the quality assurance of the curtain grouting project.5)The research direction of the related problems of the future curtain grouting technology applied in the dolomite sandifaction zone is proposed,which provides a certain idea for the follow-up research.