Model Tests And Mechanism Study Of Blasting Enhanced Permeability In Low-Permeability Sandstone-Type Uranium Deposit

In order to solve the low permeability of the ores in in-situ leach uranium mining from low-permeability sandstone-type uranium deposits, the method of blasting enhanced permeability of no free surface deep rock mass(abbreviated to BEPDR) is proposed in this thesis to increase the permeability of the ores with low permeability. A coupled damage-permeability dynamic constitutive model of rock under explosive load is developed. Based on studying the influence of different charge configurations on deep rock mass blasting effect, combined with a low-permeability sandstone-type uranium deposits in Inner Mongolia, China, the model tests of BEPDR and seepage characteristics test of the models are carried out, respectively. Then the feasibility, enhanced effect and mechanism of BEPDR are investigated. Some available conclusions are obtained and summarized as follows:1,Based on the evolved damage models, a coupled damage-permeability dynamic constitutive model of rock under explosive load is developed in this thesis. In this model it is assumed that the damage is initiated and controlled by the sum of all the principal tensile strains in place of volumetric strain at a point. The later was used in the evolved damage models to control the damage. This model doesn't distinguish whether the material is in tension state or in compression state and simulates the damage induced by differential stress. Moreover, in this model it is also assumed that the permeability of rock is isotropy and the relational expression between of damage growth and permeability variation in brittle rocks is proposed.2,Based on the succession conditions at the interface on both sides of which the pressures and velocities must be equal,the initial shock-wave parameters of the medium surrounding a charge are given by calculating the equations valid for the reflected wave in the detonation products and the equations valid for the shock wave in the medium. Damping equation of stress waves, which is damped with increased distance of wave front from the vibration source, is extended from spherical charges to cylindrical charges based on the propagation theory of wave. Then the shock-wave parameters of the rock having the same distance from the detonation source are worked out in the case of decoupled charges and coupled charges. The conclusions obtained as follows:(1) the shock-wave pressure is tens or hundreds of times larger than compressive ultimate strength of rock,then the crush zone comes into being in the rock surrounding a charge. So blasting energy are vastly dissipated;(2) in contrast with couple charge blasting,decouple charge blasting could decrease the initial shock-wave pressure of bore wall's rock. If the reasonable coefficient of decouple charge is adopted, the crush zone will disappear and the dissipation of energy will decrease;(3) water, between detonation products and rock, is indicated as an elastic buffer which protracts action time of shock wave, enlarges the action region of shock wave and increases the propagation of energy.3,Combined with a low-permeability sandstone-type uranium deposits in Inner Mongolia, China, based on the similarity theory of the model test, the preliminary model tests of BEPDR and the optimized model tests of BEPDR are designed and implemented. According to the results of the model tests, the conclusions obtain as follows: (1) blasting with coupling charging is not appropriate for BEPDR and the decoupling charging is recommended, moreover, elastic buffering effect of the decoupling medium(water) on the explosion wave is verified; (2) characteristic of homemade PVDF pressure transducer is proved, the damping relationships between blasting stress waves amplitude and distance of the wave front from the blasting source in the case of different decouple coefficients are fitting according to experimental results and this formulas could be applied in the rocks that their lithology is similar to the model; (3) the mechanism of the permeability increase of the BEPDR is preliminary revealed.4,Small-scale in situ transient pulse test system that could measure the permeability of the blasted models is developed. According to the results of the permeability of the blasted models, the conclusions obtain as follows: (1) the effect of the proposed method BEPDR on the increase of the permeability is remarkable, and compared with the permeability of original models, the permeability of blasted models is increased two or three orders of magnitude; (2) the reasonable decoupling coefficient should be within the range of 1.5~3 for the decoupling charging blast and the incidence of increasing permeability is about 70 times of the radius of charge; (3) the influence of the explosive gases and short delay blasting on the permeability is considerable.5,According to model tests of BEPDR and permeability tests of the models, the mechanism of the permeability increase of the BEPDR is revealed as follows: (1) blasting shock wave created cracks and short delay blasting action mechanism; (2) decouple charge blasting action mechanism; (3) space compensating action mechanism; (4) blasting gases driving action mechanism.At last, the research work are generalized, and the problems which need further study in the future are discussed.