Reinforcement Mechanism Of Gypsum Pillar Confined By External FRP And Its Application

The room-and-pillar mining method is currently used to extract gypsum in China.This method leads to large number of goaf areas which highly affect the safety of gypsum mining in China.The strain and acoustic emission characteristics of gypsum specimens were reinforced by Fiber Reinforced Polymer(FRP)which were monitored by donghua DH5944 dynamic strain gauge and PAC physical acoustic emission equipment.The effect ratio of high to diameter and different thickness of FRP reinforced gypsum specimen were studied experimentally.The characteristics of non-uniform distribution of the binding force along the height of specimen are analyzed by theoretical,experimental and numerical simulation methods.An optimized wrapping method is proposed due to the non-uniform distribution of binding force along the height and a constitutive model is constructed.A rock damage statistical constitutive model based on the theory of rock strain energy density and rock elastic modulus distribution,are satisfied Weibull distribution criterion.The theory of damage mechanics which can fully reflect the relationship between stress-strain and acoustic emission is used in the rock statistical constitutive model.The model was used to simulate with the characteristics of GRP-reinforced gypsum for different heights,different thickness of FRP and optimized wrap-reinforced specimens.The mining situation and lithology of No.8 mine in Dahan Gypsum Mine to analyze the stress deformation and plastic zone of the stope under,unwrapped and optimized reinforcement are based on the model.The main conclusions are as follows:(1)FRP reinforcement can significantly improve the uniaxial compressive strength and corresponding strain value of the gypsum specimens.If the height to diameter ratio is smaller,the reinforcement effect of FRP is much higher on the specimens.Different package thicknesses have smaller effect on the first stage of the stress-strain curve of FRP-reinforced gypsum specimens and there is a significant improvement in the second stage.The optimized wrapping method is proposed by considering the characteristics of the FRP-reinforced gypsum specimens with non-uniform constraining along the height direction which is better for the reinforced plaster specimens.(2)After the FRP material is reinforced,the first peak of the acoustic emission energy appears at the junction between the first stage and the second stage of the stress-strain curve.Then the acoustic emission energy curve is relatively flat,and the peak energy of the acoustic emission increases before the damage.The acoustic emission signal of the FRP-reinforced plaster specimen can reflect the accumulation and dissipation of energy.So,the damage of the specimen could be predicted by using that.(3)The FRP-reinforced gypsum test piece has non-uniformly distributed reinforcement force along the height direction.An optimized package method which has enhanced constraints at both ends,is proposed to establish the characteristics based on non-uniformly distributed reinforcement force along the height direction.According to the experimental results,the constitutive model can be simplified to a double-fold curve model.The optimized wrapping constitutive model considering the influence of diferent ratio of height to diameter is constructed.(4)The rock damage constitutive model was established based on the assumption of the elastic modulus which approximately conforms the Weibull distribution.The strain energy density theory was also used to establish the rock damage constitutive model.Based on the theory of damage mechanics,the parameters of the model are determined by the AE event energy and the velocity of the rock longitudinal wave.The statistical constitutive model of rock damage mechanics which can fully reflected the relationship between stress-strain and acoustic emission is established.(5)The statistical constitutive model of rock damage mechanics based on elastic strain energy was established by FISH language in FLAC3D which was used to simulate the reinforced gypsum specimens with different ratio of height to diameter,different thicknesses and optimized packages.The accuracy and reliability of the simulation are validated by comparing the experimental results with the simulation results.(6)Based on the model,the lithology of No.8 mine in Dahan Gypsum Mine and the mining situation are taken as the research background to analyze the stress,deformation and plastic zone of the stope under unwrapped and optimized reinforcement.The numerical simulation model was built based on the statistical constitutive model of rock damage.The stress,deformation and plastic zone range are analyzed under the room-and-pillar mining method.Then,the comparison between unwrapped condition and optimized reinforcement condition were made.The bearing capacity of pillar is remarkably enhanced under the optimized wrapping reinforcement condition.The maximum pillar displacement decreased by 33%,the maximum vertical stress of pillar decreased by 3.2%and the volume of plastic zone decreased by 39.87%.