查看更多>>摘要：Laser scanning can provide timely assessments of mine sites despite adverse challenges in the opera-tional environment.Although there are several published articles on laser scanning,there is a need to review them in the context of underground mining applications.To this end,a holistic review of laser scanning is presented including progress in 3D scanning systems,data capture/processing techniques and primary applications in underground mines.Laser scanning technology has advanced significantly in terms of mobility and mapping,but there are constraints in coherent and consistent data collection at certain mines due to feature deficiency,dynamics,and environmental influences such as dust and water.Studies suggest that laser scanning has matured over the years for change detection,clearance measurements and structure mapping applications.However,there is scope for improvements in lithol-ogy identification,surface parameter measurements,logistic tracking and autonomous navigation.Laser scanning has the potential to provide real-time solutions but the lack of infrastructure in underground mines for data transfer,geodetic networking and processing capacity remain limiting factors.Nevertheless,laser scanners are becoming an integral part of mine automation thanks to their affordabil-ity,accuracy and mobility,which should support their widespread usage in years to come.
查看更多>>摘要：Coal and gas outbursts are dynamic disasters in which a large mass of gas and coal suddenly emerges in a mining space within a split second.The interaction between the gas pressure and stress environment is one of the key factors that induce coal and gas outbursts.In this study,first,the coupling relationship between the gas pressure in the coal body ahead of the working face and the dynamic load was investi-gated using experimental observations,numerical simulations,and mine-site investigations.It was observed that the impact rate of the dynamic load on the gas-bearing coal can significantly change the gas pressure.The faster the impact rate,the speedier the increase in gas pressure.Moreover,the gas pres-sure rise was faster closer to the impact interface.Subsequently,based on engineering background,we proposed three models of stress and gas pressure distribution in the coal body ahead of the working face:static load,stress disturbance,and dynamic load conditions.Finally,the gas pressure distribution and outburst mechanism were investigated.The high concentration of gas pressure appearing at the coal body ahead of the working face was caused by the dynamic load.The gas pressure first increased grad-ually to a peak value and then decreased with increasing distance from the working face.The increase in gas pressure plays a major role in outburst initiation by resulting in the ability to more easily reach the critical points needed for outburst initiation.Moreover,the stronger the dynamic load,the greater the outburst initiation risk.The results of this study provide practical guidance for the early warning and pre-vention of coal and gas outbursts.
查看更多>>摘要：The paper proposes a three-scale binary medium-based constitutive model on the basis of the meso structures and micro components to describe the elasto-plastic mechanical behavior of mudstone sam-ples.Based on the breakage mechanism of geomaterials,mudstone samples are considered as two differ-ent materials(bonded and frictional elements)at mesoscales.From micro to meso scales,given the similar but different mineralogy composition and porosity of the bonded and frictional elements at microscale,as well as their separate mechanical characteristics,different homogenization methods are adopted to obtain their respective meso mechanical properties.At the mesoscale,in view of the unique meso structures and the continuous material transformation,the extended self-consistent scheme(SCS)is improved to be adaptable to elasto-plastic composites with varying meso components.With the con-sideration of the evolution form of the breakage ratio under the external loading being given based on the assumed strength distribution of the meso bonded elements,the mechanical relations between meso and macro scales are established.Finally,on the basis of the mean-field method and combined with the crit-ical mechanical connections between different scales,the micro-meso-macro constitutive model for mudstone samples are proposed.The model validation shows that,with a few model parameters,the pro-posed model can well reflect the stress and deformation features of mudstone samples with complex micro-components.
查看更多>>摘要：This article presents a novel approach to integrate a throughput prediction model for the ball mill into short-term stochastic production scheduling in mining complexes.The datasets for the throughput pre-diction model include penetration rates from blast hole drilling(measurement while drilling),geological domains,material types,rock density,and throughput rates of the operating mill,offering an accessible and cost-effective method compared to other geometallurgical programs.First,the comminution behav-ior of the orebody was geostatistically simulated by building additive hardness proportions from pene-tration rates.A regression model was constructed to predict throughput rates as a function of blended rock properties,which are informed by a material tracking approach in the mining complex.Finally,the throughput prediction model was integrated into a stochastic optimization model for short-term pro-duction scheduling.This way,common shortfalls of existing geometallurgical throughput prediction models,that typically ignore the non-additive nature of hardness and are not designed to interact with mine production scheduling,are overcome.A case study at the Tropicana Mining Complex shows that throughput can be predicted with an error less than 30 t/h and a correlation coefficient of up to 0.8.By integrating the prediction model and new stochastic components into optimization,the production schedule achieves weekly planned production reliably because scheduled materials match with the pre-dicted performance of the mill.Comparisons to optimization using conventional mill tonnage constraints reveal that expected production shortfalls of up to 7％per period can be mitigated this way.
查看更多>>摘要：Understanding the size effect exhibited by the fracture mechanism of anisotropic geomaterials is impor-tant for engineering practice.In this study,the anisotropic features of the nominal strength,apparent fracture toughness,effective fracture energy and fracture process zone(FPZ)size of geomaterials were first analyzed by systematic size effect fracture experiments.The results showed that the nominal strength and the apparent fracture toughness decreased with increasing bedding plane inclination angle.The larger the specimen size was,the smaller the nominal strength and the larger the apparent fracture toughness was.When the bedding inclination angle increased from 0° to 90°,the effective fracture energy and the effective FPZ size both first decreased and then increased within two complex variation stages that were bounded by the 45° bedding angle.Regardless of the inherent anisotropy of geomaterials,the nominal strength and apparent fracture toughness can be predicted by the energy-based size effect law,which demonstrates that geomaterials have obvious quasi-brittle characteristics.Theoretical analy-sis indicated that the true fracture toughness and energy dissipation can be calculated by linear elastic fracture mechanics only when the brittleness number is higher than 10;otherwise,size effect tests should be adopted to determine the fracture parameters.
查看更多>>摘要：Energy-absorbing rockbolts have been widely adopted in burst-prone excavation support,and their ser-viceability is closely related to the frequency and magnitude of seismic events.In this research,the split-tube drop test with varying impact energy was conducted to reproduce the dynamic performance of MP1 rockbolts under a wide range of seismic event magnitudes.The test results showed that the impact pro-cess could be subdivided into four distinct stages,i.e.mobilization,strain hardening,plastic flow(duc-tile),and rebound stage,of which strain hardening and plastic flow are the primary energy absorbing stages.As the impact energy per drop increases from 8.1 to 46.7 kJ,the strain rate of the shank varies between 1.20 and 2.70 s-1,and the average impact load is between 240 and 270 kN,which may be con-sidered as constant.The MP1 rockbolt has a cumulative maximum energy absorption(CMEA)of 31.9-40.0 kJ/m,with an average of 35.0 kJ/m,and the elongation rate is 11.4％-14.7％,with an average of 12.7％,both of which are negatively correlated with the impact energy per drop.Regression analysis shows that energy absorption and shank elongation,as well as momentum input and impact duration,conform to the linear relationship.The complete dynamic capacity envelope of MP1 rockbolts is pro-posed,which reflects the dynamic bearing capacity,elongation,and distinct stages.This study is helpful to better understand the dynamic characteristics of energy-absorbing rockbolts and assist design engi-neers in robust reinforcement systems design to mitigate rockburst damage in seismically active under-ground excavations.
查看更多>>摘要：The rock bridges sandwiched in incipiently jointed rock mass were considered as barriers that block the fluid seepage,and provide certain shear strength reservation.For better revealing the influence of hydraulic pressure on the failure behaviour of rock bridges,direct shear tests were carried out through a newly proposed method on rock samples that contain two parallel incipient joints.By developing the gypsum-silicone pad coupling samples,a conventional triaxial test system was qualified to imple-ment direct shear tests with satisfied sealing capability.The results showed that the rock bridges could be failed through the tensile failure,shear failure and mixed failure mechanism.The hydraulic pressure would facilitate the tensile failure mechanism and induce rougher fracture surfaces;while the normal stress would facilitate the shear failure mechanism and induce less rough fracture.The hydraulic pres-sure reduced the global shear strength of the rock block through reducing the efficient normal stress applied on the rock bridge area,which was highly dependent on the joint persistence,k.Moreover,because of the iterating occurrence of the hydraulic pressure lag with the fracture propagation,the rock bridge failure stage in the shear stress-shear displacement curves displayed a fluctuation trend.
查看更多>>摘要：The study of pressure stimulated current(PSC)changes of rocks is significant to monitor dynamic disas-ters in mines and rock masses.The existing studies focus on change laws and mechanism of currents gen-erated under the loading of rocks.An electrical and mechanics test system was established in this paper to explore the impacts of loading rates on PSCs.The results indicated that PSC curves of different rocks had different change laws under low/high loading rates.When the loading rate was relatively low,PSC curves firstly changed gently and then increased exponentially.Under high loading rates,PSC curves experienced the rapid increase stage,gentle increase stage and sudden change stage.The compressive strength could greatly affect the peak PSC in case of rock failure.The loading rate was a key factor in aver-age PSC.Under low loading rates,the variations of PSCs conformed to the damage charge model of frac-ture mechanics,while they did not at the fracture moment.Under high loading rates,the PSCs at low stress didn't fit the model due to the stress impact effects.The experimental results could provide theo-retical basis for the influence of loading rates on PSCs.
查看更多>>摘要：The Euler-Euler model is less effective in capturing the free surface of flow film in the spiral separator,and thus a Eulerian multi-fluid volume of fluid(VOF)model was first proposed to describe the particulate flow in spiral separators.In order to improve the applicability of the model in the high solid concentration system,the Bagnold effect was incorporated into the modelling framework.The capability of the pro-posed model in terms of predicting the flow film shape in a LD9 spiral separator was evaluated via com-parison with measured flow film thicknesses reported in literature.Results showed that sharp air-water and air-pulp interfaces can be obtained using the proposed model,and the shapes of the predicted flow films before and after particle addition were reasonably consistent with the observations reported in lit-erature.Furthermore,the experimental and numerical simulation of the separation of quartz and hema-tite were performed in a laboratory-scale spiral separator.When the Bagnold lift force model was considered,predictions of the grade of iron and solid concentration by mass for different trough lengths were more consistent with experimental data.In the initial development stage,the quartz particles at the bottom of the flow layer were more possible to be lifted due to the Bagnold force.Thus,a better predicted vertical stratification between quartz and hematite particles was obtained,which provided favorable conditions for subsequent radial segregation.
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