查看更多>>摘要：To investigate the attitude-switching mechanisms of existing jet slotters,which integrate drilling,punch-ing and slotting operations,and to improve its fracture ability,we used the power bond diagram theory to analyse the dynamic flow pressure,and force of slotters.A mathematical model was developed for the dynamic characteristics of slotter systems.Furthermore,to study the effect of the main characteristic parameters on the ability of the nozzle to erode sandstone,multi-orthogonal experiments were carried out.And the optimised slots were applied in later practical operations.The research results show that the inlet fluid passed through the time-varying orifice to generate pressure differential thrust,which overcame the spring force,pushed the valve core to open the side nozzle,and closed the rear cavity chan-nel thereby realising the switch of the slotter attitude.An optimal plan was established to balance the diameter,depth,and volume of punching,and a rock-breaking plan was developed for the slotter.Subsequently,the optimised water jet slotter was practically used in coal seam gas drainage.Compared with conventional dense drilling,waterjet slotting technology significantly improves the abil-ity,efficiency,and effect of increasing the permeability of the coal seam.
查看更多>>摘要：This study aims to make full use of the agricultural waste peanut shells to lower material costs and achieve cleaner production at the same time.Cellulose nanofibrils(CNF)extracted from peanut shells were mixed with acrylic acid(AA)and dimethyl diallyl ammonium chloride(DMDAAC)to prepare a new type of capsule core(dust suppressant).Then,the self-adaptive AA-DM-CNF/CA microcapsules were prepared under the action of calcium alginate.The infrared spectroscopy and X-ray diffraction analysis results suggest that AA,DMDAAC and CNF have experienced graft copolymerization which leads to the formation of an amorphous structure.The scanning electron microscopy analysis results demonstrate that the internal dust suppressant can expand and break the wall after absorbing water,featuring a self-adaptive function.Meanwhile,the laser particle size analysis results show that the microcapsules,inside which the encapsulated dust suppressant can be observed clearly,maintain a good shape.The pro-duct performance experimental results reveal that the capsule core and the capsule wall achieve syner-gistic dust suppression,thus lengthening the dust suppression time.The product boasts good dust suppression,weather resistance,degradation and synergistic combustion performances.Moreover,this study,as the first report on the development and analysis of dust-suppressing microcapsules,fills in the research gap on the reaction mechanism between dust-suppressing microcapsules and coal by MS simulation.The proposed AA-DM-CNF/CA dust-suppressing microcapsules can effectively lower the dust concentration in the space and protect the physical and mental health of coal workers.In general,this research provides a new insight into the structure control and performance enhancement of dust sup-pressants.Expanding the application range of microcapsules is of crucial economic and social benefits.
查看更多>>摘要：To reduce the cost of backfilling coal mining and utilize the underground space of coal mines,a new back-filling mining method with low backfilling rate called constructional backfilling coal mining(CBCM)is proposed.The"backfilling body-immediate roof'cooperative bearing structure of CBCM is analyzed by establishing the model of the medium thick plate on an elastic foundation.The influence of the backfilling rate on the stability of overlying strata is analyzed by the numerical simulation experiment.The control effect of CBCM is verified by a physic similar simulation test.The economic benefit of CBCM is analyzed.The conclusions are:the deformation characteristics of the immediate roof and critical backfilling spacing in CBCM can be analyzed based on the Hu Haichang's theory.Exerting the bearing capacity of the imme-diate roof is beneficial to the stability of the overlying strata.The CBCM has a good control effect on the overburden in Xinyang Mine when the backfilling rate is lower than 25％.The backfilling cost of per ton coal is 37.39 yuan/t when the backfilling rate is 13.7％,with a decrease rate of 56.63％than the full-filling.The research results can provide theoretical support for the application of CBCM in coal mining.
查看更多>>摘要：Cemented paste backfill(CPB)and rock interface interaction causes the formation of an interfacial load-ing and affects the thermal,hydraulic,mechanical,and chemical processes in bulk CPB and thus its in-situ behavior.In this study,a new meter-sized column model is developed to systematically investigate the multiphysics processes in CPB under interfacial loading.The obtained results discover that for the mechanical process,the interfacial loading leads to a reduced settlement and a weakened stress level in CPB.For the hydraulic process,lower matric suction and smaller moisture content coexist in CPB under interfacial loading.For the thermal process,the interfacial loading weakens the porosity-dependent ther-mal conduction and causes retardation in temperature variation relative to the ambient temperature.For the chemical process,weakened cement hydration with smaller electrical conductivity was observed in CPB under interfacial loading.Therefore,the obtained results reveal the linkage between the interfacial loading and multiphysics processes in CPB and thus contribute to an in-depth understanding of the mul-tiphysics behavior of CPB in underground mines.
查看更多>>摘要：This paper proposes a digital image processing-based detection algorithm for cross joint traces of coal roadway heading face.Initially,the acquired images were preprocessed,i.e.,adaptive correction was con-ducted for non-uniform illumination images based on the 2D gamma function.The edge detection algo-rithm was then applied to extract the edges of the structural plane,followed by the filtration of the non-structural plane noises.Moreover,the Hough transform algorithm was applied to extract the linear edges;finally,the edges were locally connected in accordance with the angle and distance criteria.The experimental results show that this algorithm can be used to reduce the noise caused by non-uniform illumination and avoid the mutual interference of multi-scale edges,so as to effectively extract the traces of the cross joint.Furthermore,Q-system and rock mass rating(RMR),were applied to conduct a quan-titative evaluation on the stand-up time of unsupported roof in the four test images.The Q-system qual-ity scores are 26.7,43.3,3.1,and 6.7,and the RMR quality scores are 56.84,58.73,48.42,and 51.42,respectively.The stand-up time of unsupported roofs with a span of 4.6 m are 30,36,7.7 and 14 d,respectively.
查看更多>>摘要：Although the slippage effect has been extensively studied,most of the previous studies focused on the impact of the slippage effect on apparent permeability within a low pore pressure range,resulting in the inability of matching the evolution of permeability in the remaining pressure range.In this paper,a new apparent permeability model that reveals the evolution of permeability under the combined action of effective stress and slippage in the full pore pressure range was proposed.In this model,both intrinsic permeability and slippage coefficient are stress dependent.Three experimental tests with pore pressure lower than 2 MPa and a test with pore pressure at about 10 MPa using cores from the same origin under constant confining stress and constant effective stress are conducted.By comparing experimental data and another apparent permeability model,we proved the fidelity of our newly developed model.Furthermore,the contribution factor of the slippage effect Rslip is used to determine the low pore pressure limit with significant slippage effect.Our results show that both narrow initial pore size and high effec-tive stress increase the critical pore pressure.Finally,the evolutions of the slippage coefficient and the intrinsic permeability under different boundary conditions were analyzed.
查看更多>>摘要：Ultrasonic fracturing(UF)can be used to form crack networks for oil or gas in the mining industry and hard rock excavation.In this paper,the three-dimensional internal laser-engraved crack method(3D-ILC)is introduced to make penny-shaped internal crack within the samples without any damage to the surfaces.Physical experiments were performed on the transparent samples with internal cracks at different depths.The macro-and micro-fracture fractography characteristics were focused on and ana-lyzed in details.Based on fractography,the mechanisms of the UF were revealed.The propagation paths of cracks of different depths were simulated based on the Paris fatigue model and compared with exper-imental results.The results show that the 3D-ILC method is a powerful tool for the experimental research on the internal crack propagation in the UF.Under the action of ultrasonic field,fractography shows the characteristics of beach marks,lance-like pattern,rime-like pattern and glass powder.It can be judged that the mechanisms of UF include high cycle fatigue fracture,shear fracture,and friction.The results of the numerical simulation using the Paris fatigue model are consistent with the experimental results.
查看更多>>摘要：Rolled static cracking agent(RSCA)can solve the intractable problem of traditional bulk static cracking agent(BSCA)in engineering applications.This paper innovatively studies the rational water-cement ratio of BSCA and the immersion soaking time of RSCA under the condition of controlling temperature.Through the expansion and cracking performance experiments,the development characteristics of expansion pressure,the cracking effect of the single-hole specimen and the performance of hole spraying prevention under the action of BSCA and RSCA were compared and analyzed.The results show that:(1)The volume growth rate of static cracking agent decreases with the increase of water-cement ratio,and the fluidity increases with the increase of water-cement ratio.The rational water-cement ratio for BSCA application is 0.3,and the rational immersion time of RSCA is 2-2.5 min;(2)Under the bore diameters of 30,35,40 and 45 mm,the expansion pressure of BSCA with a water-cement ratio of 0.3 is 38.2,52.3,61.5 and 68 MPa,and the expansion pressure of RSCA immersed in water for 2.5 min is 43.5,58.8,69.5 and 75.1 MPa,respectively.Among them,the development speed of expansion pressure of BSCA is higher than that of RSCA,and the arrival time of the peak expansion pressure of RSCA is 1.7 times that of BSCA;(3)The crack initiation speed of single-hole specimen under the action of RSCA is 10.3％lower than that under the action of BSCA,but the cracking speed of the former is 72.6％higher than that of the latter;(4)The hole spraying occurs in BSCA under the bore diameter of 50,55 and 60 mm,while the hole spray-ing occurs in RSCA under the bore diameter of 60 mm.In terms of bore diameter,the hole spraying pre-vention of the RSCA is better than that of BSCA.The research results enrich the static blasting technology and provide data support and theoretical reference for field application.
查看更多>>摘要：As main part of underground rock mass,the three-dimensional(3D)morphology of natural fractures plays an important role in rock mass stability.Based on previous studies on 3D morphology,this study probes into the law and mechanism regarding the influence of the confining pressure constraints on 3D morphological features of natural fractures.First,fracture surfaces were obtained by true triaxial com-pression test and 3D laser scanning.Then 3D morphological parameters of fractures were calculated by using Grasselli's model.The results show that the failure mode of granites developed by true triaxial stress can be categorized into tension failure and shear failure.Based on the spatial position of fractures,they can be divided into tension fracture surface,S-1 shear fracture surface,and S-2 shear fracture sur-face.Micro-failure of the tension fracture surface is dominated by mainly intergranular fracture;the maximum height of asperities on the fracture surface and the 3D roughness of fracture surfaces are influ-enced by σ3 only and they are greater than those of shear fracture surfaces,a lower overall uniformity than tension fracture surface.S-1 shear fracture surface and S-2 shear fracture surface are dominated by intragranular and intergranular coupling fracture.The maximum height of asperities on the fracture surface and 3D roughness of fracture surface are affected by σ1,σ2,and σ3.With the increase of σ2 orσ3,the cutting off of asperities on the fracture surface becomes more common,the maximum height of asperities and 3D roughness of fracture surface further decrease,and the overall uniformity gets fur-ther improved.The experimental results are favorable for selecting technical parameters of enhanced geothermal development and the safety of underground mine engineering.
查看更多>>摘要：To define the diffusion behavior of harmful exhaust substances from diesel vehicles and support safety risk assessments of underground coal mines,we performed a multi-species coupling calculation of the emission and diffusion of harmful substances from a trackless rubber-wheel diesel vehicle.A computa-tional fluid dynamics(CFD)model of the diffusion of harmful emissions was hence established and ver-ified.From the perspective of risk analysis,the diffusion behavior and distribution of hazardous substances emitted by the diesel vehicle were studied under 4 different conditions;moreover,we iden-tified areas characterized by hazardous levels of emissions.When the vehicle idled upwind in the road-way,high-risk areas formed behind and to the right of the vehicle:particularly high concentrations of pollutants were measured near the rear floor of the vehicle and within 5 m behind the vehicle.When the vehicle idled downwind,high-risk areas formed in front of it:particularly high concentrations of pol-lutants were measured near the floor and within 5 m from the front of the vehicle.In the above cases,the driver would not breathe highly polluted air and would be relatively safe.When the vehicle idled into the chamber,however,high-risk areas formed on both sides of the vehicle and near the upper roof.Forward entry of the vehicle caused a greater increase in the concentration of pollutants in the chamber and in the driver's breathing zone compared with reverse entry.
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