| The control of hard stratum(coal seam) has long been the emphasis and difficulty of the stratum control in coal mining. The hard coal rock exists in most mines of China. The reasonable and efficient control on the mine pressure caused by the hard stratum is a significant safeguard in the safe mining of coal. And therefore test observation, theoretical analysis and rock blasting tests on shallow surface were carried out to investigate the confined blasting(directional blasting) control mechanism, wave propagation rules, the carrying characteristics of the confined medium and the rock breaking effect of the confined blasting. The research results enjoy great theoretical and guiding significance in engineering.Study on the dynamic mechanical property under dynamic loading. The uniaxial dynamic compression tests on the rock blocks with different lithologic characters indicate that the dynamic stress-strain curves at various strain rates are similar and segmented. With the load strength changing, the rock breaking strength was distinctly related to the strain rate and was exponentially correlated with the load strength. At higher load strength, the rock block fracture was more closely related to the strain rate, the rock fragment size was smaller and the blocks increased in quantity. The hard rock at high strain rate even became powder.Study on the mechanism of wave propagation and efficient medium carrying in confined blasting. Based on the blasting, shock dynamics and fluid dynamics, the wave impedance matching among “explosive-confined medium-drilling surrounding rock” in the coal rock bore was analyzed and its effect on the wave propagation rules and the carrying characteristics of the medium were investigated. The model of shock wave propagation and confined medium stress under confined blasting was developed. The mechanism of the rock breaking orientation by the shock wave and the efficient carrying of confined medium in the confined blasting of coal rock with high safety and efficiency were revealed.Study on the rock breaking mechanism by confined(directional) blasting. The failure areas of drilling surrounding rock after confined blasting were divided according to fluid dynamics. The shock wave and stress wave oriented mechanical model of rock breaking was developed. And the fracture mechanics was used to analyze the "water wedging" action of the explosion products in drilling holes and the confined medium. The space-time action among “shock wave-stress wave-explosion products-confined medium” was revealed. Accordingly, the direction technology of the confined blasting oriented hole and the slotted pipe was put forward and also the corresponding oriented rock breaking mechanism was explained.Observation on the confined(directional) blasting and the rock breaking effect. The confined medium in the hole was proved to be efficient and even carrying by the confined blasting and hollow hole blasting tests on the cement blocks and the limestone on shallow surface. Meanwhile, the wetness, cooling and dilution of the confined medium helped control the hazardous substance produced in the confined blasting. And therefore the safe and static rock breaking by efficient explosive blasting was realized and also the super blasting dynamic load was unified with the static load of the static confined medium. The test equipment for the purpose of the confined blasting tests of coal rock and the equipment and system used in site(directional) blasting were developed. And finally the pre-fracture control theory and technology of “orientating by shock wave-rock breaking by stress wave-augmenting fracture by confined medium” under confined blasting were established preliminarily.Study on the mine pressure behaviors on the hard roof of the super thick coal seam and the implementation programs of confined(directional) blasting control on site. According to the analysis on the mine pressure behaviors of carboniferous thick coal seam in Tongxin Coal Mine of Datong Mine, the effect of bidirectional high-stress superposition on the mine pressure behaviors was revealed. Also the stress distribution characteristics of coal seam under bidirectional high stress were fitted and analyzed by the three-parameter Weibull Function. The program, i.e. transferring the high stress of the surrounding rock through implementing the pressure relief by the roof pressure-bearing directional blasting in the working face and the gob-side roadway, was put forward and the concrete technique and implementation parameters were provided.The confined blasting, as an efficient technological approach in coal rock control, has found significant application in mine pressure control, roof treatment, coal rock fracture augment, permeability improvement, the structure reconstruction, oil and gas exploitation, etc.. It is a safe, efficient, environment-friendly and energy-saving technology to guarantee the mine operation.This thesis includes 77 Figures, 13 Tables and 128 References. |
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