Understanding the thermal conductivity of granite is critical for many geological and deep engineering applications.The heated granite was subjected to air-,water-,and liquid nitrogen(LN2-)coolings in this context.The...Understanding the thermal conductivity of granite is critical for many geological and deep engineering applications.The heated granite was subjected to air-,water-,and liquid nitrogen(LN2-)coolings in this context.The transient hot-wire technique was used to determine the equivalent thermal conductivity(ETC)of the granite before and after treatment.The deterioration mechanism of ETC is analyzed from the meso-perspective.Finally,the numerical model is used to quantitatively study the impact of cooling rate on the microcrack propagation and heat conduction characteristics of granite.The results show that the ETC of granite is not only related to the heating temperature,but also affected by the cooling rate.The ETC of granite decreases nonlinearly with increasing heating temperature.A faster cooling rate causes a greater decrease in ETC at the same heating temperature.The higher the heating temperature,the stronger the influence of cooling rate on ETC.The main explanation for the decrease in ETC of granite is the increase in porosity and microcrack density produced by the formation and propagation of pore structure and microcracks during heating and cooling.Further analysis displays that the damage of granite at the heating stage is induced by the difference in thermal expansion and elastic properties of mineral particles.At the cooling stage,the faster cooling rate causes a higher temperature gradient,which in turn produces greater thermal stress.As a result,it not only causes new cracks in the granite,but also aggravates the damage at the heating stage,which induces a further decrease in the heat conduction performance of granite,and this scenario is more obvious at higher temperatures.展开更多
High geo-temperature is one of the inevitable geological disasters in deep engineering such as resource extraction,space development,and energy utilization.One of the key issues is to understand the mechanical propert...High geo-temperature is one of the inevitable geological disasters in deep engineering such as resource extraction,space development,and energy utilization.One of the key issues is to understand the mechanical properties and failure mechanism of high-temperature rock disturbed by low-temperature airflow after excavation.Therefore,.the experimental and numerical investigation were carried out to study the impact of cooling rate on mechanical properties and failure mechanism of high temperature sandstone.First,uniaxial compression experiments of high temperature sandstone at different real-time cooling rates were carried out to study the mechanical properties and failure modes.The experimental results indicate that the cooling rate has a significant effect on the mechanical properties and failure modes of sandstone.The peak strain,peak stress,and elastic modulus decrease with an increase in cooling rate,and the fragmentation degree after failure increases gradually.Moreover,the equivalent numerical model of heterogeneous sandstone was established using particle flow code(PFC)to reveal the failure mechanism.The results indicate that the sandstone is dominated by intragrain failure in the cooling stage,the number of microcracks is exponentially related to the cooling rate,and the higher the cooling rate,the more cracks are concentrated in the exterior region.Under axial loading,the tensile stress is mostly distributed along the radial direction,and the damage in the cooling stage is mostly due to the fracture of the radial bond.In addition,axial loading,temperature gradient and thermal stress mismatch between adjacent minerals are the main reasons for the damage of sandstone in the cooling stage.Moreover,the excessive temperature gradient in the exterior region of the sandstone is the main reason for the damage concentration in this region.展开更多
With the increasing exploitation scope and intensity,the shallow resources would be exhausted in the future;and the deep mining will become an essential choice.In deep tunnel engineering,the heat-harm becomes one of t...With the increasing exploitation scope and intensity,the shallow resources would be exhausted in the future;and the deep mining will become an essential choice.In deep tunnel engineering,the heat-harm becomes one of the mainbariers.Investigations on high temperature coal mine have been done in Nothem China,with the construting of threemodels of high temperature mines suffering heat-harm,at the Jiahe mine,Sanhejian mine and Zhangshuanglou mine.Thedomestic and abroad cooling technologies of the mine respectively are also summarized after comparatively analyzing theadvantages and disadvantages of each technology.Finally,we find that the high temperature exchange machinery system(HEMS)technology that use mine discharge as the cold source,is excellent to heat-ham control in deep mines.Taking theJiahe coal mine as an example,we systematically introduce this teclnology by disposing three main workstations.HEMStechnology with its operations and functions in different exploitation levels are accomplished,including the extraction ofrefrigerating output,the transportation of chilled water by closed circulation line,the decompression of circulation linesand equipment by pressure transformation machine,and the heat exchange and cooling of workplace by heat exchangebetween wind stream and the chilled water.The exchanged heat source from the workplace is taken to ground heating bythe circulating water which acts as a carrier.It shows that the HEMS-technology benefit in environment protection andemission reduction.Results of this project illustrate that it is efficient in heat-ham control with the temperature decrease ofthe workplace down to 26-29℃,and being 4-6℃ lower than the original,and the relative humidity 5%-15%lowerthan before.It greatly improves the working environment of underground workplace suffering heat-ham of high tem-perature and high humidity.In addition,by the extracting of deep geothermal enery,ground fired boiler for heating hasbeen replaced,reducing environmental pollution.This technology is worth generalization in deep mines and related fields.展开更多
The understanding of the weakening mechanism of tensile strength of rock subjected to cyclic wetting-drying is critical for rock engineering.Tensile strength tests were conducted on a total of 35 sandstone specimens w...The understanding of the weakening mechanism of tensile strength of rock subjected to cyclic wetting-drying is critical for rock engineering.Tensile strength tests were conducted on a total of 35 sandstone specimens with different wetting-drying cycles.The crack propagation process and acoustic emission characteristics of the tested samples were obtained through a high-speed camera and acoustic emission system.The results indicate that the tensile strength is observably reduced after cyclic wetting-drying,and the extent of the reduction is not only related to the number of wettingdrying cycle,but also closely related to the clay mineral content of the sample.In addition,as the cycles of wetting-drying increase,the effect of each single cycle on tensile strength get reduced until it becomes constant.Moreover,the crack initiation and penetration time is prolonged as the number of wetting-drying cycle increases,which indicates that cyclic wetting-drying weakens the rock stiffness and enhances the ductility of sandstone.Meanwhile,the acoustic emission characteristics of the tested samples further confirmed the ductile behaviour of the sandstone samples with increasing wetting-drying cycle.Furthermore,through the analysis of the microstructure and mineral composition of the samples with different wetting-drying cycles,it is concluded that the main weakening mechanisms of sandstones containing clay minerals are frictional reduction,chemical and corrosive deterioration.展开更多
A large number of mines are closed or abandoned every year in China.Geothermal utilization is one of the important ways to efficiently reuse underground resources in abandoned mines.How to calculate the volume and dis...A large number of mines are closed or abandoned every year in China.Geothermal utilization is one of the important ways to efficiently reuse underground resources in abandoned mines.How to calculate the volume and distribution of underground water storage space is the key to accurately evaluate the sustainable geothermal production in abandoned mines.In this paper,according to the multi-scale characteristics of the underground space in abandoned mine,the flow and heat transfer equations in the multi-scale space are sorted out systematically,and the calculation methods of different secondary space volumes are derived in detail.Taking Jiahe abandoned mine as the background,the volume and distribution of underground secondary space are calculated,and three heat storage evaluation models considering different water storage spaces are established by using COMSOL.The simulation results show that there are great differences among different models,and the results of the equivalent porous media model considering the multi-scale space are most consistent with the reality.Sensitivity analyses of key parameters model results indicated that the heat production is closely related to not only the recharge flow rate but also the recharge temperature and operating time.Furthermore,the energy saving and emission reduction benefits of geothermal utilization in abandoned mines are calculated,the results show that geothermal utilization of abandoned mines can effectively reduce energy consumption and CO_(2)emissions,and it has great economic benefits.展开更多
基金the Natural Science Foundation of China(Grant No.42241145)supported by the Natural Science Foundation of China(Grant No.41941018)General Projects for Scientific and Technological Innovation of China Coal Science and Industry Group(Grant No.2022-MS001).
文摘Understanding the thermal conductivity of granite is critical for many geological and deep engineering applications.The heated granite was subjected to air-,water-,and liquid nitrogen(LN2-)coolings in this context.The transient hot-wire technique was used to determine the equivalent thermal conductivity(ETC)of the granite before and after treatment.The deterioration mechanism of ETC is analyzed from the meso-perspective.Finally,the numerical model is used to quantitatively study the impact of cooling rate on the microcrack propagation and heat conduction characteristics of granite.The results show that the ETC of granite is not only related to the heating temperature,but also affected by the cooling rate.The ETC of granite decreases nonlinearly with increasing heating temperature.A faster cooling rate causes a greater decrease in ETC at the same heating temperature.The higher the heating temperature,the stronger the influence of cooling rate on ETC.The main explanation for the decrease in ETC of granite is the increase in porosity and microcrack density produced by the formation and propagation of pore structure and microcracks during heating and cooling.Further analysis displays that the damage of granite at the heating stage is induced by the difference in thermal expansion and elastic properties of mineral particles.At the cooling stage,the faster cooling rate causes a higher temperature gradient,which in turn produces greater thermal stress.As a result,it not only causes new cracks in the granite,but also aggravates the damage at the heating stage,which induces a further decrease in the heat conduction performance of granite,and this scenario is more obvious at higher temperatures.
基金supported by the National Natural Science Foundation of China (41941018)supported by Beijing Natural Science Foundation (8212033)+1 种基金supported by the Fundamental Research Funds for the Central Universities (2021YJSLI13,2021JCCXLJ05)supported by Innovation Fund Research Project (SKLGDUEK202221).
文摘High geo-temperature is one of the inevitable geological disasters in deep engineering such as resource extraction,space development,and energy utilization.One of the key issues is to understand the mechanical properties and failure mechanism of high-temperature rock disturbed by low-temperature airflow after excavation.Therefore,.the experimental and numerical investigation were carried out to study the impact of cooling rate on mechanical properties and failure mechanism of high temperature sandstone.First,uniaxial compression experiments of high temperature sandstone at different real-time cooling rates were carried out to study the mechanical properties and failure modes.The experimental results indicate that the cooling rate has a significant effect on the mechanical properties and failure modes of sandstone.The peak strain,peak stress,and elastic modulus decrease with an increase in cooling rate,and the fragmentation degree after failure increases gradually.Moreover,the equivalent numerical model of heterogeneous sandstone was established using particle flow code(PFC)to reveal the failure mechanism.The results indicate that the sandstone is dominated by intragrain failure in the cooling stage,the number of microcracks is exponentially related to the cooling rate,and the higher the cooling rate,the more cracks are concentrated in the exterior region.Under axial loading,the tensile stress is mostly distributed along the radial direction,and the damage in the cooling stage is mostly due to the fracture of the radial bond.In addition,axial loading,temperature gradient and thermal stress mismatch between adjacent minerals are the main reasons for the damage of sandstone in the cooling stage.Moreover,the excessive temperature gradient in the exterior region of the sandstone is the main reason for the damage concentration in this region.
基金support by the Key Program of National Natural Science Foundation of China(51134005)Doctoral Scientific Fund Project of the Ministry of Education of China(20120023120004)is gratefully acknowledged.
文摘With the increasing exploitation scope and intensity,the shallow resources would be exhausted in the future;and the deep mining will become an essential choice.In deep tunnel engineering,the heat-harm becomes one of the mainbariers.Investigations on high temperature coal mine have been done in Nothem China,with the construting of threemodels of high temperature mines suffering heat-harm,at the Jiahe mine,Sanhejian mine and Zhangshuanglou mine.Thedomestic and abroad cooling technologies of the mine respectively are also summarized after comparatively analyzing theadvantages and disadvantages of each technology.Finally,we find that the high temperature exchange machinery system(HEMS)technology that use mine discharge as the cold source,is excellent to heat-ham control in deep mines.Taking theJiahe coal mine as an example,we systematically introduce this teclnology by disposing three main workstations.HEMStechnology with its operations and functions in different exploitation levels are accomplished,including the extraction ofrefrigerating output,the transportation of chilled water by closed circulation line,the decompression of circulation linesand equipment by pressure transformation machine,and the heat exchange and cooling of workplace by heat exchangebetween wind stream and the chilled water.The exchanged heat source from the workplace is taken to ground heating bythe circulating water which acts as a carrier.It shows that the HEMS-technology benefit in environment protection andemission reduction.Results of this project illustrate that it is efficient in heat-ham control with the temperature decrease ofthe workplace down to 26-29℃,and being 4-6℃ lower than the original,and the relative humidity 5%-15%lowerthan before.It greatly improves the working environment of underground workplace suffering heat-ham of high tem-perature and high humidity.In addition,by the extracting of deep geothermal enery,ground fired boiler for heating hasbeen replaced,reducing environmental pollution.This technology is worth generalization in deep mines and related fields.
基金Funding for this work was provided by Natural Science Foundation of China(41941018,41402273),the Yue Qi Scholar Program of China University of Mining and Technology.The authors wish to thank the reviewers for careful and constructive suggestions.
文摘The understanding of the weakening mechanism of tensile strength of rock subjected to cyclic wetting-drying is critical for rock engineering.Tensile strength tests were conducted on a total of 35 sandstone specimens with different wetting-drying cycles.The crack propagation process and acoustic emission characteristics of the tested samples were obtained through a high-speed camera and acoustic emission system.The results indicate that the tensile strength is observably reduced after cyclic wetting-drying,and the extent of the reduction is not only related to the number of wettingdrying cycle,but also closely related to the clay mineral content of the sample.In addition,as the cycles of wetting-drying increase,the effect of each single cycle on tensile strength get reduced until it becomes constant.Moreover,the crack initiation and penetration time is prolonged as the number of wetting-drying cycle increases,which indicates that cyclic wetting-drying weakens the rock stiffness and enhances the ductility of sandstone.Meanwhile,the acoustic emission characteristics of the tested samples further confirmed the ductile behaviour of the sandstone samples with increasing wetting-drying cycle.Furthermore,through the analysis of the microstructure and mineral composition of the samples with different wetting-drying cycles,it is concluded that the main weakening mechanisms of sandstones containing clay minerals are frictional reduction,chemical and corrosive deterioration.
基金supported by the Beijing Natural Science Foundation(8212033)the Fundamental Research Funds for the Central Universities(2021JCCXLJ05)innovation fund research project(SKLGDUEK202221).
文摘A large number of mines are closed or abandoned every year in China.Geothermal utilization is one of the important ways to efficiently reuse underground resources in abandoned mines.How to calculate the volume and distribution of underground water storage space is the key to accurately evaluate the sustainable geothermal production in abandoned mines.In this paper,according to the multi-scale characteristics of the underground space in abandoned mine,the flow and heat transfer equations in the multi-scale space are sorted out systematically,and the calculation methods of different secondary space volumes are derived in detail.Taking Jiahe abandoned mine as the background,the volume and distribution of underground secondary space are calculated,and three heat storage evaluation models considering different water storage spaces are established by using COMSOL.The simulation results show that there are great differences among different models,and the results of the equivalent porous media model considering the multi-scale space are most consistent with the reality.Sensitivity analyses of key parameters model results indicated that the heat production is closely related to not only the recharge flow rate but also the recharge temperature and operating time.Furthermore,the energy saving and emission reduction benefits of geothermal utilization in abandoned mines are calculated,the results show that geothermal utilization of abandoned mines can effectively reduce energy consumption and CO_(2)emissions,and it has great economic benefits.
