Deformation And Failure And Bolting Grouting Reinforcement Mechanism Of Coal Pillar Near The Goaf Under Unilateral Water With Low Pressure

The roadway driving along next goaf is widely used in coal mining.Generally,small coal pillar is left to isolate the roadway from the goaf,preventing water and harmful gases from the goaf from entering the roadway.However,under the condition of water accumulation in the goaf,although the water pressure is very low,the accumulated water will cause the bearing capacity of the coal pillar to decrease,the deformation to be intensified or even destroyed,and the accumulated water will easily penetrate into the roadway,causing floor heave of the roadway.In this thesis,coal pillar near the goaf under unilateral water with low pressure is the main research object.The combination of field measurement,rock mechanics experiment,similar material experiment and numerical simulation were used to construct different scale numerical simulation network models based on the statistical rules on field crack fissures,obtain the deformation and failure characteristics and permeability characteristics of coal pillar under unilateral water with low pressure,reveal the deformation and failure and bolting grouting reinforcement mechanism of coal pillar under unilateral water with low pressure.The main tasks as follows:(1)Numerical simulation model of small-scale coal samples with cracks based on the statistical law of cracks were established and verified.A small-scale numerical model with cracks reflecting the distribution of the crack was established by using the software UDEC based on crack distribution law obtained by the field drilling peep.The mechanical properties,failure characteristics and cracks development of the specimens in uniaxial compression,Brazilian splitting and variable angle shear experiments were simulated,and compared with laboratory experimental results,the correctness of the numerical model was verified.(2)Compressive deformation failure and permeability characteristics of coal sample under unilateral water with low pressure were researched.The unilateral water with low pressure permeation experiment of coal sample was carried out by using a one-sided hydraulic loading device designed and developed for cylindrical specimen seepage experiments,the compressive deformation and failure characteristics and permeability characteristics of coal samples under unilateral low water pressure were revealed.Based on the small-scale numerical model with cracks obtained in(1),the flow-solid coupling constitutive relation in UDEC was used to verify and further analyze the compressive deformation and failure characteristics and permeability characteristics of coal samples.(3)The ratio about "solid-liquid" coupling similar material ratio was analysed by experiment.A comprehensive experiment was carried out on the proportioning of similar materials with sand and barite powder as aggregate and paraffin as cement.The mechanical properties and failure morphology of the specimens were analyzed,and the relationship between physical mechanics parameters and different ratio was obtained.The material ratio that can be used in fluid-solid coupling similar simulation experiment was obtained.(4)The stability of coal pillar and roadway surrounding rock near the goaf under unilateral water with low pressure was researched by similar simulation.Designed and developed a fluid-solid coupling similar model experiment platform.Used the material ratio obtained by(3),asimilar model experiment on deformation and failure of coal pillar and roadway surrounding rock near the goaf under unilateral water was obtained.The deformation and failure laws and the permeability characteristics of coal pillar near the goaf were studied.(5)The crack grading on the width of the coal pillar was given based on the statistical law of cracks and combined with ultrasonic testing.A large-scale coal pillar crack network distribution model based on crack grading was obtained.Combined with UDEC soft,used flow-solid coupling constitutive relation,the deformation characteristics of coal pillar and roadway surrounding rock were simulated when the coal pillar width and unilateral water pressure changed.The limit coal pillar width,deformation characteristics of the coal pillar and roadway surrounding rock and the coal pillar permeability characteristics were obtained.(6)The deformation and failure mechanism of coal pillar near the goaf under unilateral low water pressure was researched.Combined deformation and failure characteristics and laws of coal sample and coal pillar under unilateral low water pressure,revealed the deformation and failure mechanism of the coal pillar near the goaf under unilateral low water pressure.(7)The bolting grouting reinforcement mechanism of coal pillar near the goaf under unilateral low water pressure was researched.Based on the analysis of the original roadway support effect,the bolting grouting reinforcement scheme on coal pillar near the goaf was proposed.Based on the large-scale coal pillar network model obtained in(6),used UDEC with the fluid-solid coupling constitutive relation,simulated and analyzed reinforcement effect and reinforcement mechanism of bolting grouting.