Ventilation is one of the radon control measures in an underground working environment.However,the dynamics related to the cave mining methods particularly in block/panel cave mines,complicate the design of effective ...Ventilation is one of the radon control measures in an underground working environment.However,the dynamics related to the cave mining methods particularly in block/panel cave mines,complicate the design of effective ventilation system,and implementation.Events such as hang ups(in the drawbells),leakage from old workings,and changes in cave porosity lead to differing response of an existing ventilation designs.However,it is difficult to investigate these conditions at the mine or with a laboratory scale study.Therefore,this study develops a discrete model to investigate the impact of different radon control measures in cave mines using computational fluid dynamics techniques.We considered two ventilation conditions for a fully developed cave:with and without the undercut ventilation.For each of the two conditions,we studied four parameters:airflow distribution through the production drifts,radon distribution through the production drifts,the effect of increasing airflow on radon concentration,and the effect of a cave top negative pressure on radon distribution.The results show that:the undercut ventilation significantly increases the radon concentration in the production drift;the growth of radon concentration through the production drift is nonlinear(oscillating pattern);maintaining a negative pressure on top of the cave is more effective at mitigating radon exposure,when the undercut ventilation is active;and increase in air volume flow rate decreases radon concentration in most regions,however,there might be regions with significant radon accumulation due to pressure variation across the drifts.These findings provide vital information for designing an effective ventilation system and for proactive implementation of radon control measures in cave mines.展开更多
The configuration of an airway(or production drift)in panel cave mines is different from the typical(straight)mine airway designs.The drawpoints are connected to the airway(cross-cuts),which allows airflow from the ca...The configuration of an airway(or production drift)in panel cave mines is different from the typical(straight)mine airway designs.The drawpoints are connected to the airway(cross-cuts),which allows airflow from the cave into the airway or air loss from the airway into the cave due to the ventilation approach and cave porosity.These affect airflow in the production drifts,but it is difficult to investigate these conditions from field or laboratory scaled studies.Therefore,this study develops discrete and continuum computational fluid dynamics(CFD)models to study the effects of the ventilation approach and cave porosity on the airway resistance.Our findings show that:with active undercut ventilation,a unique resistance model is required for the airway in panel cave mines;and an increase in cave porosity decreases the drift’s resistance.These findings provide essential tools for a panel cave ventilation design.展开更多
为了从宏观-细观角度探究不同形状矿石颗粒的破碎强度、破碎模式、碎块尺寸分布及断口表面形貌等破碎特性,首先,基于三维扫描技术重构矿石颗粒图像,获取颗粒形状参数;其次,定量表征矿石颗粒外部宏观层次轮廓形态及细观层次凹凸度;最后,...为了从宏观-细观角度探究不同形状矿石颗粒的破碎强度、破碎模式、碎块尺寸分布及断口表面形貌等破碎特性,首先,基于三维扫描技术重构矿石颗粒图像,获取颗粒形状参数;其次,定量表征矿石颗粒外部宏观层次轮廓形态及细观层次凹凸度;最后,对扫描后的几何平均粒径范围为20~45 mm的不规则磁铁矿矿石颗粒进行单颗粒压缩破碎试验,并重构颗粒断口表面以定量探究断面粗糙度的影响因素。研究结果表明:矿石颗粒的破碎强度分布可用Weibull函数模型拟合,其中Weibull参数m为2.17,特征强度F0为7.20 k N;矿石颗粒破碎模式分为边部磨损、中部破碎、贯通缝破坏、随机开裂4种类型;中部破碎为主要破碎模式,占比为0.433,“第一尺寸碎块”及“第二尺寸碎块”质量分数分布均符合正态分布,均值分别在0.65和0.30左右;但当颗粒3个主维度长度接近时,颗粒不容易发生中部破碎。以分形维数D定量表征颗粒破碎断口表面粗糙度,当截面面积大于36 mm^(2)时,分形维数D更稳定。球度显著影响颗粒破碎断口表面平均分形维数D,扁平度、能量、棱角度及等效粒径4种因素影响程度次之且相近,延伸率的影响不存在统计学差异。展开更多
基金financial support from the National Institute for Occupational Safety and Health (NIOSH) (No. 200-2014-59613) for conducting this research
文摘Ventilation is one of the radon control measures in an underground working environment.However,the dynamics related to the cave mining methods particularly in block/panel cave mines,complicate the design of effective ventilation system,and implementation.Events such as hang ups(in the drawbells),leakage from old workings,and changes in cave porosity lead to differing response of an existing ventilation designs.However,it is difficult to investigate these conditions at the mine or with a laboratory scale study.Therefore,this study develops a discrete model to investigate the impact of different radon control measures in cave mines using computational fluid dynamics techniques.We considered two ventilation conditions for a fully developed cave:with and without the undercut ventilation.For each of the two conditions,we studied four parameters:airflow distribution through the production drifts,radon distribution through the production drifts,the effect of increasing airflow on radon concentration,and the effect of a cave top negative pressure on radon distribution.The results show that:the undercut ventilation significantly increases the radon concentration in the production drift;the growth of radon concentration through the production drift is nonlinear(oscillating pattern);maintaining a negative pressure on top of the cave is more effective at mitigating radon exposure,when the undercut ventilation is active;and increase in air volume flow rate decreases radon concentration in most regions,however,there might be regions with significant radon accumulation due to pressure variation across the drifts.These findings provide vital information for designing an effective ventilation system and for proactive implementation of radon control measures in cave mines.
基金support from the National Institute for Occupational Safety and Health(NIOSH)(No.200-2014-59613)for conducting this research.
文摘The configuration of an airway(or production drift)in panel cave mines is different from the typical(straight)mine airway designs.The drawpoints are connected to the airway(cross-cuts),which allows airflow from the cave into the airway or air loss from the airway into the cave due to the ventilation approach and cave porosity.These affect airflow in the production drifts,but it is difficult to investigate these conditions from field or laboratory scaled studies.Therefore,this study develops discrete and continuum computational fluid dynamics(CFD)models to study the effects of the ventilation approach and cave porosity on the airway resistance.Our findings show that:with active undercut ventilation,a unique resistance model is required for the airway in panel cave mines;and an increase in cave porosity decreases the drift’s resistance.These findings provide essential tools for a panel cave ventilation design.
文摘为了从宏观-细观角度探究不同形状矿石颗粒的破碎强度、破碎模式、碎块尺寸分布及断口表面形貌等破碎特性,首先,基于三维扫描技术重构矿石颗粒图像,获取颗粒形状参数;其次,定量表征矿石颗粒外部宏观层次轮廓形态及细观层次凹凸度;最后,对扫描后的几何平均粒径范围为20~45 mm的不规则磁铁矿矿石颗粒进行单颗粒压缩破碎试验,并重构颗粒断口表面以定量探究断面粗糙度的影响因素。研究结果表明:矿石颗粒的破碎强度分布可用Weibull函数模型拟合,其中Weibull参数m为2.17,特征强度F0为7.20 k N;矿石颗粒破碎模式分为边部磨损、中部破碎、贯通缝破坏、随机开裂4种类型;中部破碎为主要破碎模式,占比为0.433,“第一尺寸碎块”及“第二尺寸碎块”质量分数分布均符合正态分布,均值分别在0.65和0.30左右;但当颗粒3个主维度长度接近时,颗粒不容易发生中部破碎。以分形维数D定量表征颗粒破碎断口表面粗糙度,当截面面积大于36 mm^(2)时,分形维数D更稳定。球度显著影响颗粒破碎断口表面平均分形维数D,扁平度、能量、棱角度及等效粒径4种因素影响程度次之且相近,延伸率的影响不存在统计学差异。
