| As one of the most common unfavorable geological bodies in the process of underground engineering construction,fractured rock mass is easy to cause geological disasters such as engineering instability and water inrush,and grouting reinforcement is the most common and effective prevention and control method at present.However,as the most important grouting material,ordinary cement grout is easy to show heterogeneity under the action of gravity,which affects the grouting construction effect.Therefore,it is necessary to conduct a deeper analysis of the internal and external performance of the physical and mechanical properties of cement grout.This paper takes tunnel grouting engineering as the background and combines theoretical analysis,laboratory test and numerical simulation.The heterogeneous development of cement grout under gravity segregation effect and its influence on grouting reinforcement effect of fractured rock mass are studied from both micro and macro aspects,which supplement the relevant theoretical system and provide a new test method and research idea.The main work and innovation achievements of this paper are as follows:(1)The gravity segregation process of cement grout is analyzed and summarized,and a normalized theoretical model of pore ratio of grout considering the influence of hydration is put forward.Then,the finite strain and small strain theoretical models of pore ratio of grout stone body in gravity segregation are established by assuming the limit condition of consolidation time.(2)The gravity segregation tests of cement grout with different water-cement ratios and different heights were carried out,and the gradient variation of pore size distribution and pore ratio in the direction of gravity was tested and analyzed by nuclear magnetic resonance technology,and the theoretical model of pore ratio was compared and verified by pore ratio test data.Finally,the formula for calculating the compressive strength of cement grout stone body is established by fitting the relation between the pore ratio of the stone body and the compressive strength.(3)A kind of observation and sampling device for gravity segregation of cement grout is designed,which solves the problem that it is difficult to extract samples from inside the grout.XRD phase analysis and scanning electron microscopy were used to compare the phase composition and microscopic pore structure of grout stone body,and the influence of selfgravity segregation on hydration products and degree of hydration was summarized(4)The influence of complex fracture flow network on grout gravity segregation process was studied by grout filling experiment.Nuclear magnetic resonance technology and uniaxial compression test were used to summarize the development law of the pore ratio and compressive strength of the added solid in the direction of gravity,and by controlling the variable roughness of the medium,it was concluded that the bond property of the slurry would also show a gradient change in the direction of gravity.Finally,the discrete element software PFC3D was used to analyze the failure mechanism of solid addition.(5)A fracture grouting filling test method was proposed to achieve the segmentalized acquisition of samples filled with slurry in gravity direction.The shear strength and failure modes of each specimen were compared by shear test,and the microscopic morphological characteristics of the interface between slurry and fracture plane were analyzed and evaluated by microscopic scanning electron microscopy.Finally,the heterogeneity of cement grout reinforcement effect on fractured rock mass under gravity segregation effect is summarized from both micro and macro aspects. |
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