In order to study the failure mechanism of backfill and the reasonable matches between backfill and rock mass, and to achieve the object of safe and efficient mining in metal mine, four types of backfills were tested ...In order to study the failure mechanism of backfill and the reasonable matches between backfill and rock mass, and to achieve the object of safe and efficient mining in metal mine, four types of backfills were tested under uniaxial compression loading, with cement?tailing ratios of 0.250:1, 0.125:1, 0.100:1 and 0.083:1, respectively. With the help of the stress?strain curves, the deformation and failure characteristics of different backfills with differing cement?tailing ratios were analyzed. Based on the experimental results, the damage constitutive equations of cemented backfills with four cement?tailing ratios were proposed on the basis of damage mechanics. Moreover, comparative analysis of constitutive model and experimental results were made to verify the reliability of the damage model. In addition, an energy model using catastrophe theory to obtain the instability criteria of system was established to study the interaction between backfill and rock mass, and then the system instability criterion was deduced. The results show that there are different damage characteristics for different backfills, backfills with lower cement?tailing ratio tend to have a lower damage value when stress reaches peak value, and damage more rapidly and more obviously in failure process after peak value of stress; the stiffness and elastic modulus of rock mass with lower strength are more likely to lead to system instability. The results of this work provide a scientific basis for the rational strength design of backfill mine.展开更多
Cemented tailings backfill(CTB) have increasingly been used in recent years to improve the stability of mining stopes in deep underground mines. Deep mining processes are often associated with rock bursting and high-s...Cemented tailings backfill(CTB) have increasingly been used in recent years to improve the stability of mining stopes in deep underground mines. Deep mining processes are often associated with rock bursting and high-speed dynamic loading conditions. Therefore, it is important to investigate the characteristics and dynamic mechanical behavior of CTB. This paper presents the results of dynamic tests on CTB specimens with different cement and solid contents using a split Hopkinson pressure bar(SHPB). The results showed that some CTB specimens exhibited one to two lower stress peaks after reaching dynamic peak stress before they completely failed. The greater the cement-to-tailings ratio is, the more obvious the strain reaction. This property mainly manifested as follows. First,the dynamic peak stress increased with the increase of the cement-to-tailings ratio when the impact velocity was fixed. Second, the dynamic peak stress had a quadratic relationship with the average stress rate. Third, the cement-to-tailings ratio could enhance the increase rate of dynamic peak stress with strain rate. In addition, the dynamic strength enhancement factor K increased with the increase of strain rate, and its value was larger than that of the rock samples. The failure modes of CTB specimens under low-speed impact were tensile failure and X conjugate shear failure, where were nearly the same as those under static uniaxial and triaxial compression. The CTB specimens were crushed and broken under critical strain, a failure mode similar to that of low-strength concrete. The results of the experimental research can improve the understanding of the dynamic mechanical properties of CTB and guide the strength design of deep mining backfills.展开更多
In this study, a pressure cell apparatus is developed to investigate the early age evolution of the strength and deformation behaviour of cemented paste backfill(CPB) when subjected to various loading conditions under...In this study, a pressure cell apparatus is developed to investigate the early age evolution of the strength and deformation behaviour of cemented paste backfill(CPB) when subjected to various loading conditions under different curing scenarios. The different curing scenarios that are simulated include:(1)drained and undrained conditions,(2) different filling rates,(3) different filling sequences, and(4) different curing stresses. The findings show that drainage, curing stress, curing time and filling rate influence the mechanical and deformation behaviours of CPB materials. The coupled effects of consolidation, drainage and suction contribute to the strength development of drained CPB subjected to curing stress. On the other hand, particle rearrangement caused by the applied pressure and suction development due to self-desiccation plays a significant role in the strength gain of undrained CPB cured under stress.Furthermore, curing stress induces slightly faster rate of cement hydration, which can contribute to strength acquisition.展开更多
In recent years,field trials of non-pillar longwall mining using complete backfill have been implemented successively in the Chinese coal mining industry.The objective of this paper is to get a scientific understandin...In recent years,field trials of non-pillar longwall mining using complete backfill have been implemented successively in the Chinese coal mining industry.The objective of this paper is to get a scientific understanding of surface subsidence control effect using such techniques.It begins with a brief overview on complete backfill methods primarily used in China,followed by an analysis of collected subsidence factors under mining with complete backfill.It is concluded that non-pillar longwall panel layout cannot protect surface structures against damages at a relatively large mining height,even though complete backfill is conducted.In such cases,separated longwall panel layout should be applied,i.e.,panel width should be subcritical and stable coal pillars should be left between the adjacent panels.The proposed method takes the principles of subcritical extraction and partial extraction;in conjunction with gob backfilling,surface subsidence can be effectively mitigated,thus protecting surface buildings against mining-induced damage.A general design principle and method of separated panel layout have also been proposed.展开更多
Along with slurry concentration and particle density,particle size distribution(PSD)of tailings also exerts a significant influence on the yield stress of cemented paste,a non-Newtonian fluid.In this work,a paste stab...Along with slurry concentration and particle density,particle size distribution(PSD)of tailings also exerts a significant influence on the yield stress of cemented paste,a non-Newtonian fluid.In this work,a paste stability coefficient(PSC)was proposed to characterize paste gradation and better reveal its connection to yield stress.This coefficient was proved beneficial to the construction of a unified rheological model,applicable to different materials in different mines,so as to promote the application of rheology in the pipeline transportation of paste.From the results,yield stress showed an exponential growth with increasing PSC,which reflected the proportion of solid particle concentration to the packing density of granular media in a unit volume of slurry,and could represent the properties of both slurry and granular media.It was found that slurry of low PSC contained extensive pores,generally around 20μm,encouraging free flow of water,constituting a relatively low yield stress.In contrast,slurry of high PSC had a compact and quite stable honeycomb structure,with pore sizes generally<5μm,causing the paste to overcome a higher yield stress to flow.展开更多
基金Projects(2013BAB02B05,2012BAB08B01)supported by the National Science and Technology Support Program of ChinaProject(2013JSJJ029)supported by the Teacher Foundation of Central South University,ChinaProject(51074177)supported by the Joint Funding of National Natural Science Foundation and Shanghai Baosteel Group Corporation,China
文摘In order to study the failure mechanism of backfill and the reasonable matches between backfill and rock mass, and to achieve the object of safe and efficient mining in metal mine, four types of backfills were tested under uniaxial compression loading, with cement?tailing ratios of 0.250:1, 0.125:1, 0.100:1 and 0.083:1, respectively. With the help of the stress?strain curves, the deformation and failure characteristics of different backfills with differing cement?tailing ratios were analyzed. Based on the experimental results, the damage constitutive equations of cemented backfills with four cement?tailing ratios were proposed on the basis of damage mechanics. Moreover, comparative analysis of constitutive model and experimental results were made to verify the reliability of the damage model. In addition, an energy model using catastrophe theory to obtain the instability criteria of system was established to study the interaction between backfill and rock mass, and then the system instability criterion was deduced. The results show that there are different damage characteristics for different backfills, backfills with lower cement?tailing ratio tend to have a lower damage value when stress reaches peak value, and damage more rapidly and more obviously in failure process after peak value of stress; the stiffness and elastic modulus of rock mass with lower strength are more likely to lead to system instability. The results of this work provide a scientific basis for the rational strength design of backfill mine.
基金financially supported by the National Key R&D Program of China (No. 2018YFC0604602)the Fundamental Research Funds for the Central Universities of China (No. FRF-TP-17-029A2)the Open fund of Key Laboratory of High-Efficient Mining and Safety of Metal Mines, Ministry of Education of China (No. ustbmslab201803)
文摘Cemented tailings backfill(CTB) have increasingly been used in recent years to improve the stability of mining stopes in deep underground mines. Deep mining processes are often associated with rock bursting and high-speed dynamic loading conditions. Therefore, it is important to investigate the characteristics and dynamic mechanical behavior of CTB. This paper presents the results of dynamic tests on CTB specimens with different cement and solid contents using a split Hopkinson pressure bar(SHPB). The results showed that some CTB specimens exhibited one to two lower stress peaks after reaching dynamic peak stress before they completely failed. The greater the cement-to-tailings ratio is, the more obvious the strain reaction. This property mainly manifested as follows. First,the dynamic peak stress increased with the increase of the cement-to-tailings ratio when the impact velocity was fixed. Second, the dynamic peak stress had a quadratic relationship with the average stress rate. Third, the cement-to-tailings ratio could enhance the increase rate of dynamic peak stress with strain rate. In addition, the dynamic strength enhancement factor K increased with the increase of strain rate, and its value was larger than that of the rock samples. The failure modes of CTB specimens under low-speed impact were tensile failure and X conjugate shear failure, where were nearly the same as those under static uniaxial and triaxial compression. The CTB specimens were crushed and broken under critical strain, a failure mode similar to that of low-strength concrete. The results of the experimental research can improve the understanding of the dynamic mechanical properties of CTB and guide the strength design of deep mining backfills.
基金the Natural Sciences and Engineering Research Council of Canada (NSERC)the University of Ottawa
文摘In this study, a pressure cell apparatus is developed to investigate the early age evolution of the strength and deformation behaviour of cemented paste backfill(CPB) when subjected to various loading conditions under different curing scenarios. The different curing scenarios that are simulated include:(1)drained and undrained conditions,(2) different filling rates,(3) different filling sequences, and(4) different curing stresses. The findings show that drainage, curing stress, curing time and filling rate influence the mechanical and deformation behaviours of CPB materials. The coupled effects of consolidation, drainage and suction contribute to the strength development of drained CPB subjected to curing stress. On the other hand, particle rearrangement caused by the applied pressure and suction development due to self-desiccation plays a significant role in the strength gain of undrained CPB cured under stress.Furthermore, curing stress induces slightly faster rate of cement hydration, which can contribute to strength acquisition.
文摘In recent years,field trials of non-pillar longwall mining using complete backfill have been implemented successively in the Chinese coal mining industry.The objective of this paper is to get a scientific understanding of surface subsidence control effect using such techniques.It begins with a brief overview on complete backfill methods primarily used in China,followed by an analysis of collected subsidence factors under mining with complete backfill.It is concluded that non-pillar longwall panel layout cannot protect surface structures against damages at a relatively large mining height,even though complete backfill is conducted.In such cases,separated longwall panel layout should be applied,i.e.,panel width should be subcritical and stable coal pillars should be left between the adjacent panels.The proposed method takes the principles of subcritical extraction and partial extraction;in conjunction with gob backfilling,surface subsidence can be effectively mitigated,thus protecting surface buildings against mining-induced damage.A general design principle and method of separated panel layout have also been proposed.
基金financially supported by China Postdoctoral Science Foundation (No. 2019M663576)the National Natural Science Foundation of China (No. 51774020)+2 种基金the Key Laboratory of Ministry of Education of China for Efficient Mining and Safety of Metal Mines (No. ustbmslab201801)the Program for Innovative Research Team (in Science and Technology) in University of Yunnan Provincethe Research Start-up Fund for Introduced Talent of Kunming University of Science and Technology (No. KKSY201821024)
文摘Along with slurry concentration and particle density,particle size distribution(PSD)of tailings also exerts a significant influence on the yield stress of cemented paste,a non-Newtonian fluid.In this work,a paste stability coefficient(PSC)was proposed to characterize paste gradation and better reveal its connection to yield stress.This coefficient was proved beneficial to the construction of a unified rheological model,applicable to different materials in different mines,so as to promote the application of rheology in the pipeline transportation of paste.From the results,yield stress showed an exponential growth with increasing PSC,which reflected the proportion of solid particle concentration to the packing density of granular media in a unit volume of slurry,and could represent the properties of both slurry and granular media.It was found that slurry of low PSC contained extensive pores,generally around 20μm,encouraging free flow of water,constituting a relatively low yield stress.In contrast,slurry of high PSC had a compact and quite stable honeycomb structure,with pore sizes generally<5μm,causing the paste to overcome a higher yield stress to flow.
