微波处理玄武岩强度的SPH-FEM耦合算法模拟

微波预处理弱化岩体强度,进而降低机械破岩过程中的钻头/刀具磨损、提升凿岩效率已经成为一项极具前景的技术。为探究数值模拟参数对岩石静强度模拟结果的影响,并为后续钻凿或岩石切割模拟确定合理的微波处理玄武岩数值力学参数,采用光滑粒子流体动力学与有限元耦合算法(SPH-FEM)构建岩石单轴压缩与巴西拉伸数值模型。为减小微波损伤对岩石强度测试误差的影响,采用线性莫尔-库仑理论对相同微波参数下微波处理玄武岩试样的黏聚力和内摩擦角进行标定。在单轴抗压与巴西拉伸模拟过程中开展SPH关键控制参数的敏感性分析,并根据同一组校核后的黏聚力和内摩擦角数据,在数值实验中同时捕获目标抗压强度与巴西拉伸强度,单轴抗压强度数值模拟结果与试验结果吻合较好。此外,结合数值模拟结果评估微波辐照参数对玄武岩力学行为的影响。

Drill bit wear monitoring and failure prediction for mining automation

This article introduces a novel approach for tricone bit wear condition monitoring and failure prediction for surface mining applications.A successful bit health monitoring system is essential to achieve fully autonomous blasthole drilling.In this research in-situ vibration signals were analyzed in timefrequency domain and signals trend during tricone bit life span were investigated and introduced to support the development of artificial intelligence(AI)models.In addition to the signal statistical features,wavelet packet energy distribution proved to be a powerful indicator for bit wear assessment.Backpropagation artificial neural network(ANN)models were designed,trained and evaluated for bit state classification.Finally,an ANN architecture and feature vector were introduced to classify the bit condition and predict the bit failure.

Numerical and experimental analyses of rock failure mechanisms due to microwave treatment

Despite the extensive studies conducted on the effectiveness of microwave treatment as a novel rock preconditioning method,there is yet to find reliable data on the rock failure mechanisms due to microwave heating.In addition,there is no significant discussion on the energy efficiency of the method as one of the important factors among the mining and geotechnical engineers in the industry.This study presents a novel experimental method to evaluate two main rock failure mechanisms due to microwave treatment without applying any mechanical forces,i.e.distributed and concentrated heating.The result shows that the existence of a small and concentrated fraction of a strong microwave absorbing mineral will change the failure mechanism from the distributed heating to the concentrated heating,which can increase the weakening over microwave efficiency(WOME)by more than 10 folds.This observation is further investigated using the developed coupled numerical model.It is shown that at the same input energy,the existence of microwave absorbing minerals can cause major heat concentration inside the rock and increase the maximum temperature by up to three times.

The influence of microwave irradiation on rocks for microwaveassisted underground excavation

Demand is growing for explosive-free rock breakage systems for civil and mining engineering, and spaceindustry applications. This paper highlights the work being undertaken in the Geomechanics Laboratoryof McGill University to make a real application of microwave-assisted mechanical rock breakage to fullfacetunneling machines and drilling. Comprehensive laboratory tests investigated the effect of microwaveradiation on temperature profiles and strength reduction in hard rocks （norite, granite, and basalt）for a range of exposure times and microwave power levels. The heating rate on the surface of the rockspecimens linearly decreased with distance between the sample and the microwave antenna, regardlessof microwave power level and exposure time. Tensile and uniaxial compressive strengths were reducedwith increasing exposure time and power level. Scanning electron micrographs （SEMs） highlightedfracture development in treated basalt. It was concluded that the microwave power level has a strongpositive influence on the amount of heat damage induced to the rock surface. Numerical simulations ofelectric field intensity and wave propagation conducted with COMSOL Multiphysics
software generatedtemperature profiles that were in close agreement with experimental results.

Experimental investigation on the effects of microwave irradiation on kimberlite and granite rocks

This study is a part of an overall research project on the effects of microwave(MW)irradiation on rocks for assisted rock breaking systems as well as mineral processing at McGill University.For the first time,this paper highlights a comprehensive investigation on the effects of microwave irradiation on Canadian kimberlites.Potential contribution to the continuous rock excavation and rock weakening effect prior to implementation of mechanical techniques was explored.Two different kimberlite rocks,i.e.volcaniclastic kimberlite(VK)and hypabyssal kimberlite(HK),and granite samples were studied.Some important physical properties of the rock samples were measured including rock quality designation(RQD),specific gravity,porosity,and specific heat capacity.Rock samples were treated for various exposure times using a multi-mode MWunit at different power levels ranging from 2 kW to 15 kW.The effect of MW irradiation on rock samples was investigated.The results indicate that the mechanical properties including unconfined compressive strength(UCS)and Brazilian tensile strength(BTS)were significantly dropped as a result of MWirradiation.Finally,the effect on rock abrasivity using the Cerchar abrasivity index(CAI)has also been discussed.

Drilling signals analysis for tricone bit condition monitoring

This paper presents a novel approach to investigate the relations between drilling signals and bit wear condition in real world full-scale mining operations.This research addresses the increasing demand for automation in mining to increase the efficiency,safety,and ability to work in harsh environments.A crucial issue in fully autonomous unmanned drilling is to have a system to detect the bit wear condition through the drilling signals analysis in real time.In this work,based on extensive field studies,a novel qualitative method for tricone bit wear state classification is developed and introduced.The relations between drilling vibration as well as electric motor current signals and bit wear are investigated and bit failure vibration frequencies,regardless of the geological conditions,are introduced.Bit failure frequencies are experimentally investigated and analytically calculated.Finally,the effect of bit design parameters on the failure frequencies is presented for the application of bit wear condition monitoring and bit failure prediction.

Guest editorial-special issue on advances in mine ventilation in 2019

Ventilation has always been an integral part of underground mining operations.As surface and shallow deposits are depleting,extracting ores from deeper underground levels is becoming more and more common,and is expected to grow in the future[1].Rising environmental awareness,energy cost and implementation of carbon tax in some countries have led the mining industry to look for cleaner alternatives[2].

Stability analysis of slopes with planar failure using variational calculus and numerical methods

This study investigates the technique of variational calculus applied to estimate the slope stability considering the mechanism of planar failure.The critical plane failure surface should be determined because it theoretically indicates the most unfavorable plane to be considered when stabilizing a slope to rectify the instability generated by several statistically possible planes.This generates integrals that can be solved by numerical methods,such as the Newton Cotes and the finite differences methods.Additionally,a system of nonlinear equations is obtained and solved.The surface of the critical planar failure is determined by applying the condition of transversality in mobile boundaries,for which various examples are provided.The number of slices is varied in one of the examples,while the surface of the critical planar failure is determined in the others.Results are compared using analytical methods through axis rotations.All the results obtained by considering normal stress,safety factors,and critical planar failure are nearly the same;however,in this research,a study is carried out for“n”number of slices using programming methods.Sub-routines are important because they can be applied in slopes with different geometry,surcharge,interstitial pressure,and pseudo-static load.