| Most coal mines in Western China are Jurassic coal measure strata,and the water bearing sandstone of Zhiluo formation is argillaceous cementation,which has the characteristics of water Sandy and argillaceous,poor injectability and so on.There is little research on the grouting mechanism of this kind of rock stratum at home and abroad,and the theoretical results are difficult to guide the engineering practice.Safety accidents such as shaft water outflow and roadway surrounding rock instability often occur due to grouting failure.Therefore,taking the water bearing sandstone of Jurassic Zhiluo Formation in the western mining area as the research object,the research on the crack propagation characteristics and influencing factors of splitting grouting in this kind of sandstone has certain theoretical guiding significance and engineering application value for clarifying its grouting crack propagation and slurry diffusion mechanism and guiding grouting engineering practice.Using the research method of combining laboratory test and numerical simulation,this paper carried out the mechanical and permeability characteristics test of Jurassic sandstone,the hydraulic fracturing test of Jurassic sandstone under true triaxial condition,and numerically simulated and analyzed the fracture propagation characteristics and influencing factors of Jurassic sandstone splitting grouting.The main research contents and results are as follows:1.The cementation of Jurassic sandstone was observed by NMR and SEM,and its pore structure was analyzed;The stress seepage coupling test was carried out.The study shows that the main mineral compositions of Jurassic sandstone samples are quartz,feldspar,calcite and mica,which are mainly argillaceous pore cementation;Its permeability is positively and negatively correlated with osmotic pressure and confining pressure respectively,and finally tends to be a stable value with the increase of confining pressure.2.Six groups of hydraulic fracturing tests of Jurassic sandstone under true triaxial conditions were carried out.The results show that the crack initiation pressure decreases with the increase of horizontal stress difference,which is verified by theoretical calculation;The crack produced by hydraulic fracturing is basically a single main crack,and the crack is always perpendicular to the minimum principal stress surface.With the increase of horizontal stress difference,the crack produced by grouting splitting tends to be more straight and single;When the horizontal stress difference is larger,the difference between the crack initiation pressure test and the theoretical maximum value is smaller;During the whole test,the acoustic emission signal activity is strong,but the amplitude is small,and the acoustic emission activity signal decreases with the increase of confining pressure.3.Based on ABAQUS / soil module,through the prefabricated cohesive element to simulate crack expansion,several two-dimensional numerical simulation models of grouting in single fractured rock mass are established,and the crack initiation pressure,crack expansion law and its influencing factors are analyzed.The results show that the fracture initiation pressure is negatively correlated with the horizontal pressure difference and the rock permeability coefficient,and the slurry injection rate has a small effect on the fracture initiation pressure,and the effect of slurry viscosity on the fracture initiation pressure can be ignored;the fracture width is positively correlated with the injection rate and slurry viscosity and the curve growth rate is getting smaller,and the fracture width decreases linearly with the increase of the horizontal stress difference.Figure [48] Table [6] Reference [87]... |
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