Study On The Influence And Control Of Grouting Vein Shape On Grouting Effect

Fracture grouting is a process in which grout is injected into soil with an applied pressure to improve the engineering properties of the soil.Fracture grouting has been successfully applied in engineering practice to raise the bearing capacity,to reduce the permeability,and to compensate for the surface settlements induced by tunneling.The fracture grouting in soft clay ground will form a branched cement frame and compressed clay mass around,leading to a significant increase in compression modulus and decrease in permeability of the resulted composite mass.Up to now,fracture grouting is predominantly an empirical procedure.Most of the existing research focused on the fracturing mechanism and the pressure determination of hydraulic fracturing,while few studies have been conducted on the process of fracturing propagation,the direction and shape of fractures,the reinforcement effects.Especially for the study of hydraulic fracturing in soil,there is no calculation method to describe the shape and propagation of fractures in soil.The main reason is that the research methods of hydraulic fracturing are insufficient.Because hydraulic fracturing occurs in the interior of rock and soil,and involves the effect of fluid-solid coupling,it is not easy to be observed and measured.Due to the lack of systematic experiments and research,a perfect method system has not been formed,which brings difficulties to design and construction.In view of the shortcomings of the existing research results,this paper focuses on the influence of grouting vein shape on grouting reinforcement.The main research contents and results are as follows:(1)Full-scale test was used to observe the initiation and propagation process of grouting veins.The strength,permeability coefficient,compressive modulus and dry density of clay around grouting veins were measured at different water cement ratios,and compared with those of non-grouting clay.The compressive modulus and permeability coefficient of composite composed of clay and grouting body were measured.The test results show that in fracture grouting,the grouting effect is not only affected by the proportion of grouting materials,but also by the shape of grouting veins.(2)By establishing the theoretical calculation formulas of compression modulus and permeability coefficient of composite,the influence of grouting vein shape on grouting reinforcement effect is studied quantitatively,and the influence of grouting vein shape on reinforcement and seepage prevention effect is analyzed.The effects of grouting vein angle,length,length-width ratio and soil compression are calculated.The results show that the shape of grouting vein has a significant effect on grouting reinforcement and seepage prevention.(3)It is difficult to observe the process of hydraulic fracturing directly.The propagation of fractures in soils is usually inferred from indirect measurements.In recent years,with the development of numerical simulation,the finite element method provides a new idea for the research of fracture grouting.The finite element method(FEM)and fluid volume function(VOF)are proposed to simulate the fracture grouting process in soil.The numerical model adopts fluid,stress and damage coupling analysis method to simulate the fracture propagation process.The hydration process of slurry is described by the change of slurry elastic modulus and viscosity with time.The numerical simulation shows the process of fracture initiation,secondary fracturing and propagation in homogeneous and heterogeneous soils.The proposed numerical method can not only simulate fracture grouting,but also present the whole process of compaction grouting and seepage grouting.The numerical simulation results are in good agreement with the field and test results,which further proves the applicability and accuracy of the method.(4)At present,the researches mostly focus on the initiation pressure in rock strata,but few studies have been done on the factors affecting the effect of grouting reinforcement,especially on the propagation of grouting veins after initiation and the shape of grouting veins,and how to control the shape of grouting veins to achieve the optimal reinforcement and anti-seepage effect.Aiming at the shape of slurry vein formed by fracturing,the influence of fracture grouting parameters and technology is analyzed by using the proposed simulation method,and the relevant laws and parameters and technology for controlling the shape of slurry vein are studied.(5)The research results are applied to a practical project.In view of the unsatisfactory grouting effect in practical engineering,a new grouting scheme is put forward through simulation analysis,which optimizes the grouting process,improves the grouting effect,ensures the safe construction of the project,and verifies the correctness of the research conclusions in this paper.