查看更多>>摘要：Isolated pillars in underground mines are subjected to uniaxial stress,and the load bearing cross-section of pillars is commonly rectangularly shaped.In addition,the uniaxial compression test(UCT)is widely used for determining the basic mechanical properties of rocks and revealing the mechanism of isolated pillar disasters under unidimensional stress.The shape effects of rock mechanical properties under uni-axial compression are mainly quantitatively reflected in the specific shape ratios of rocks.Therefore,it is necessary to study the detailed shape ratio effects on the mechanical properties of rectangular prism rock specimens and isolated pillars under uniaxial compressive stress.In this study,granite,marble and sand-stone rectangular prism specimens with various height to width ratios(r)and width to thickness ratios(u)were prepared and tested.The study results show that r and u have a great influence on the bearing ability of rocks,and thin or high rocks have lower uniaxial compressive strength.Reducing the level of r can enhance the u effect on the strength of rocks,and increasing the level of u can enhance the r effect on the strength of rocks.The lateral strain on the thickness side of the rock specimen is larger than that on the width side,which implies that crack growth occurs easily on the thickness side.Considering r and u,a novel strength prediction model of isolated pillars was proposed based on the testing results,and the pre-diction model was used for the safety assessment of 179 isolated pillars in the Xianglu Mountain Tungsten Mine.
查看更多>>摘要：Rapid advances in deep-sea mining engineering have created an urgent need for the accurate evaluation of the undrained strength of marine soils,especially surface soils.Significant achievements have been made using full-flow penetration penetrometers to evaluate marine soil strength in the deep penetration;however,a method considering the effect of ambient water on the surface penetration needs to be estab-lished urgently.In this study,penetrometers with multiple probes were developed and used to conduct centrifuge experiments on South China Sea soil and kaolin clay.First,the forces on the probes throughout the penetration process were systematically analyzed and quantified.Second,the spatial influence zone was determined by capturing the resistance changes and sample crack development,and the penetration depth for a sample to reach a stable failure mode was given.Third,the vane shear strength was used to invert the penetration resistance factor of the ball and determine the range of the penetration resistance factor values.Furthermore,a methodology to determine the penetration resistance factors for surface marine soils was established.Finally,the effect of the water cavity above various probes in the surface penetration was used to formulate an internal mechanism for variations in the penetration resistance factor.
查看更多>>摘要：The long-term stability of the roof is particularly important in designing underground rock structures.To estimate the durability of roof strata in underground excavation,a computation scheme of subcritical crack growth is proposed in this study.By adopting the proposed method,the potential collapse location of strata is derivable in accordance with a static model,the durability of roof strata can be estimated,a dynamic time step control strategy is achieved to balance the accuracy and speed of computing,and the initial crack size of rock can be estimated.In addition to the above,a mechanical model of underground excavation with non-uniformly distributed loads and partially yielded foundation is presented as the pro-totypical case.A set of case studies is carried out that showcase a power correlation between applied stress and roof durability.The allowable applied tensile stress for a 100-year life cycle is about 76％of the tensile strength.By using the proposed subcritical crack growth computation scheme,the roof stabil-ity in an underground excavation can be identified not only from the spatial view but also from the tem-poral perspective.
查看更多>>摘要：To improve the efficiency of coal seam water injection,the influence of nanofluids on coal surface wet-tability was studied based on the nano drag reduction and injection enhancement technology in the field of tertiary oil recovery.The composition optimization and performance evaluation of nanofluids with nano-silica and sodium lauryl sulfate as the main components were carried out,and the effects of the nanofluid with the optimal ratio on coal wettability were studied through spontaneous upward imbibi-tion experiments.The results show that the composite nanofluid has a lower surface tension,and the lowest value of the interfacial tension is 15.79 mN/m.Therefore,the composite nanofluid can enhance the wettability of coal.However,its effects on coal samples with different metamorphic degrees is differ-ent,that is,low rank coal is the largest,middle rank coal is the second,and high rank coal is the least.In addition,a functional relationship between time and imbibition height is found for pulverized coal with different particle sizes.When the particle size of pulverized coal is 60-80 mesh,the wettability of nano-fluid to coal is best.The findings in this paper provide a new perspective for improving the water injection efficiency for coal seams with low permeability.
查看更多>>摘要：Temperature affects the flotation of quartz in the calcium/sodium oleate(NaOL)system,while there is a lack of understanding of its potential mechanism.Therefore,in this work,the flotation response of quartz to temperature was investigated via micro-flotation experiments,interface property analyses,and theo-retical calculations.Flotation results demonstrated that increasing temperature contributed to higher flotation recovery of quartz,which enhanced the removal of quartz from hematite.Surface tension results revealed that higher temperatures lowered the critical micelle concentration(CMC)and surface tension of the NaOL solution,and thus enhanced its surface activity.Solution chemistry calculations and X-ray photoelectron spectroscopy(XPS)measurements confirmed that the increased content of Ca(OH)+achieved by increasing temperatures enhanced the adsorption amounts of calcium species(acting as acti-vation sites)on the quartz surface.Dynamic light scattering(DLS)measurements verified that the asso-ciation degree of RCOO-to form(RCOO)22-was strengthened.Furthermore,adsorption density measurements and molecular dynamics(MD)simulations confirmed that increasing the temperature facilitated NaOL adsorption toward the surface of the quartz,which was attributed to the stronger inter-action between NaOL and the calcium-activated quartz surface at higher temperatures.As a result,quartz flotation was improved by increasing temperatures.Accordingly,a possible adsorption model was proposed.
查看更多>>摘要：Pore network structure of ore body is a diffusion channel of leaching agent solution that exerts a signif-icant influence on seepage.The ore body structure,pore distribution,pore and throat size,and pore net-work characteristics of topsoil,weathered,and semiweathered layers of ionic rare earth ore in southern Jiangxi Province were explored in this study.The effect of leaching operation on the pore structure was investigated,and main factors affecting the seepage were analyzed.Results showed that the semiweath-ered layer presents a dense structure and a small number of unconnected pores.Pores of topsoil and weathered layers are mainly long and narrow column openings with some planar fractures.Even pore distribution and large size span were observed.Compared with the weathered layer,the topsoil layer demonstrates larger voids,smaller average pore volume and equivalent radius,and fewer coordination throats;however,the average equivalent radius of the throat in the topsoil layer is larger and large-scale channels exist through ore body vertically.Hence,permeability of the topsoil layer is significantly higher than that of the weathered layer.Colloidal clay minerals migrate easily and the occurrence of silt-ing in the small porosity blocks the throat and significantly decreases the permeability of the ore body in the leaching process.The equivalent radius of the throat is the key to the seepage.Reducing the migration of fine particles is an effective measure to protect the throat and shorten the leaching period.
查看更多>>摘要：With the gradual depletion of shallow coal resources,the Yanzhou mine in China will enter the lower coal seam mining phase.However,as mining depth increases,lower coal seam mining in Yanzhou is threat-ened by water inrush in the Benxi Formation limestone and Ordovician limestone.The existing prediction models for the water burst at the bottom of the coal seam are less accurate than expected owing to var-ious controlling factors and their intrinsic links.By analyzing the hydrogeological exploration data of the Baodian lower seam and combining the results of the water inrush coefficient method and the Yanzhou mine pressure seepage test,an evaluation model of the seepage barrier capacity of the fault was estab-lished.The evaluation results show the water of the underlying limestone aquifer in the Baodian mine area mainly threatens the lower coal mining through the fault fracture zone.The security of mining above confined aquifer in the Baodian mine area gradually decreases from southwest to northeast.By compar-ing the water inrush coefficient method and the evaluation model of fault impermeability,the results show the evaluation model based on seepage barrier conditions is closer to the actual situation when analyzing the water breakout situation at the working face.
查看更多>>摘要：The characterization of micro-surface mechanical and electrical properties of the natural rock materials remains inadequate,and their macroscopic performance can be better comprehended by investigating the surface properties.With this purpose,the present research focuses on characterizing the micro-surface morphology,Derjaguin-Muller-Toporov(DMT)modulus,adhesion,and potential of granite,shale,and limestone by employing the atomic force microscope(AFM)as a pioneer attempt.The results show that the micro-surface morphology of the rock fluctuates within hundreds of nanometers,among which the granite micro-surface is comparatively the smoothest,followed by limestone.The morphology of the shale is the roughest,indicating that the regional difference of shale micro-surface is dominant.The dis-tribution of the adhesion on rock micro-surface is uneven;the average adhesion of eight measuring areas for shale is 23.93 nN,accounting for three times of granite and limestone,while the surface DMT modulus of shale is relatively lower than granite and limestone.It is inferred from the obtained results that higher surface adhesion is helpful to the gas adsorption of shale,and the lower surface DMT(elastic)modulus is useful to the formation of fractures and pores.Thus,these two are the micromechanical basis of shale gas adsorption.Additionally,introducing a method to reduce the surface adhesion will benefit the explo-ration of unconventional resources such as shale gas.The micro-surface of the three types of rocks all shows electricity,with average potential ranging from tens of millivolts to hundreds of millivolts.Besides,the micro-surface potential of the rocks are heterogeneous,and both positive and negative points can be found.The existence and uneven distribution of micro-surface potential provide a robust physical basis for the electromagnetic radiation generated by rock fracture under loading.This study offers a new method for revealing the adsorption characteristics of unconventional gas reservoir rocks and the electro-magnetic radiation mechanism of the rock fracture.
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