Estimating shear strength of high-level pillars supported with cemented backfilling using the HoekeBrown strength criterion

Deep metal mines are often mined using the high-level pillars with subsequent cementation backfilling(HLSCB)mining method.At the design stage,it is therefore important to have a reasonable method for determining the shear strength of the high-level pillars(i.e.cohesion and internal friction angle)when they are supported by cemented backfilling.In this study,a formula was derived for the upper limit of the confining pressure σ3max on a high-level pillar supported by cemented backfilling in a deep metal mine.A new method of estimating the shear strength of such pillars was then proposed based on the Hoek eBrown failure criterion.Our analysis indicates that the horizontal stress σhh acting on the cemented backfill pillar can be simplified by expressing it as a constant value.A reasonable and effective value for σ3max can then be determined.The value of s3max predicted using the proposed method is generally less than 3 MPa.Within this range,the shear strength of the high-level pillar is accurately calculated using the equivalent MohreCoulomb theory.The proposed method can effectively avoid the calculation of inaccurate shear strength values for the high-level pillars when the original HoekeBrown criterion is used in the presence of large confining pressures,i.e.the situation in which the cohesion value is too large and the friction angle is too small can effectively be avoided.The proposed method is applied to a deep metal mine in China that is being excavated using the HLSCB method.The shear strength parameters of the high-level pillars obtained using the proposed method were input in the numerical simulations.The numerical results show that the recommended level heights and sizes of the high-level pillars and rooms in the mine are rational.

Investigation of stress-induced progressive failure of mine pillars using a Voronoi grain-based breakable block model

The Voronoi grain-based breakable block model(VGBBM)based on the combined finite-discrete element method(FDEM)was proposed to explicitly characterize the failure mechanism and predict the deformation behavior of hard-rock mine pillars.The influence of the microscopic parameters on the macroscopic mechanical behavior was investigated using laboratory-scale models.The field-scale pillar models(width-to-height,W/H=1,2 and 3)were calibrated based on the empirically predicted stress-strain curves of Creighton mine pillars.The results indicated that as the W/H ratios increased,the VGBBM effectively predicted the transition from strain-softening to pseudo-ductile behavior in pillars,and explicitly captured the separated rock slabs and the V-shaped damage zones on both sides of pillars and conjugate shear bands in core zones of pillars.The volumetric strain field revealed significant compressional deformation in core zones of pillars.While the peak strains of W/H=1 and 2 pillars were relatively consistent,there were significant differences in the strain energy storage and release mechanism.W/H was the primary factor influencing the deformation and strain energy in the pillar core.The friction coefficient of the structural plane was also an important factor affecting the pillar strength and the weakest discontinuity angle.The fracture surface was controlled by the discontinuity angle and the friction coefficient.This study demonstrated the capability of the VGBBM in predicting the strengths and deformation behavior of hard-rock pillars in deep mine design.

Pillar effect induced by ultrahigh phosphorous/nitrogen doping enables graphene/MXene film with excellent cycling stability for alkali metal ion storage

Graphene's large theoretical surface area and high conductivity make it an attractive anode material for potassium-ion batteries(PIBs).However,its practical application is hindered by small interlayer distance and long ion transfer distance.Herein,this paper aims to address the issue by introducing MXene through a simple and scalable method for assembling graphene and realizing ultrahigh P doping content.The findings reveal that MXene and P-C bonds have a "pillar effect" on the structure of graphene,and the P-C bond plays a primary role.In addition,N/P co-doping introduces abundant defects,providing more active sites for K^(+) storage and facilitating K^(+) adsorption.As expected,the developed ultrahigh phosphorous/nitrogen co-doped flexible reduced graphene oxide/MXene(NPrGM) electrode exhibits remarkable reversible discharge capacity(554 mA hg^(-1) at 0.05 A g^(-1)),impressive rate capability(178 mA h g^(-1) at 2 A g^(-1)),and robust cyclic stability(0.0005% decay per cycle after 10,000 cycles at 2 A g^(-1)).Furthermore,the assembled activated carbon‖NPrGM potassium-ion hybrid capacitor(PIHC) can deliver an impressive energy density of 131 W h kg^(-1) and stable cycling performance with 98.1% capacitance retention after5000 cycles at 1 A g^(-1).Such a new strategy will effectively promote the practical application of graphene materials in PIBs/PIHCs and open new avenues for the scalable development of flexible films based on two-dimensional materials for potential applications in energy storage,thermal interface,and electromagnetic shielding.

Numerical and theoretical study of load transfer behavior during cascading pillar failure

To further study the load transfer mechanism of roofemulti-pillarefloor system during cascading pillar failure(CPF),numerical simulation and theoretical analysis were carried out to study the three CPF modes according to the previous experimental study on treble-pillar specimens,e.g.successive failure mode(SFM),domino failure mode(DFM)and compound failure mode(CFM).Based on the finite element code rock failure process analysis(RFPA^(2D)),numerical models of treble-pillar specimen with different mechanical properties were established to reproduce and verify the experimental results of the three CPF modes.Numerical results show that the elastic rebound of roofefloor system induced by pillar instability causes dynamic disturbance to adjacent pillars,resulting in sudden load increases and sudden jump displacement of adjacent pillars.The phenomena of load transfer in the roofemulti-pillarefloor system,as well as the induced accelerated damage behavior in adjacent pillars,were discovered and studied.In addition,based on the catastrophe theory and the proposed mechanical model of treble-pillar specimen edisc spring group system,a potential function that characterizes the evolution characteristics of roof emulti-pillarefloor system was established.The analytical expressions of sudden jump and energy release of treble-pillar specimenedisc spring group system of the three CPF modes were derived according to the potential function.The numerical and theoretical results show good agreement with the experimental results.This study further reveals the physical essence of load transfer during CPF of roof emulti-pillarefloor system,which provides references for mine design,construction and disaster prevention.

Stability prediction of hard rock pillar using support vector machine optimized by three metaheuristic algorithms

Hard rock pillar is one of the important structures in engineering design and excavation in underground mines.Accurate and convenient prediction of pillar stability is of great significance for underground space safety.This paper aims to develop hybrid support vector machine(SVM)models improved by three metaheuristic algorithms known as grey wolf optimizer(GWO),whale optimization algorithm(WOA)and sparrow search algorithm(SSA)for predicting the hard rock pillar stability.An integrated dataset containing 306 hard rock pillars was established to generate hybrid SVM models.Five parameters including pillar height,pillar width,ratio of pillar width to height,uniaxial compressive strength and pillar stress were set as input parameters.Two global indices,three local indices and the receiver operating characteristic(ROC)curve with the area under the ROC curve(AUC)were utilized to evaluate all hybrid models’performance.The results confirmed that the SSA-SVM model is the best prediction model with the highest values of all global indices and local indices.Nevertheless,the performance of the SSASVM model for predicting the unstable pillar(AUC:0.899)is not as good as those for stable(AUC:0.975)and failed pillars(AUC:0.990).To verify the effectiveness of the proposed models,5 field cases were investigated in a metal mine and other 5 cases were collected from several published works.The validation results indicated that the SSA-SVM model obtained a considerable accuracy,which means that the combination of SVM and metaheuristic algorithms is a feasible approach to predict the pillar stability.

Lateral abutment pressure distribution and evolution in wide pillars under the first mining effect

The wide pillars are generally popular due to the high productivity and efficiency in Northwest China.The distribution of lateral abutment pressure in coal pillars is important for mining safety.To reveal the effect of the first mining on the lateral abutment pressure distribution and evolution in wide pillars,an in-situ experiment,theoretical analysis and numerical simulation were performed.First,the field monitoring of lateral abutment pressure was conducted from the perspective of time and space in the Chahasu Coal Mine,Huangling No.2 Coal Mine and Lingdong Coal Mine during the first mining.Based on the field monitoring stress,a theoretical model was proposed to reveal the lateral abutment pressure distribution.The methodology was demonstrated through a case study.Aiming at the distribution mechanism,a numerical experiment was conducted through the finite-discrete element method(FDEM).Last,field observations of borehole fractures were performed to further study the damage distribution.In addition,two types of lateral abutment pressure evolution with mining advance were discussed.Suggestions on the stress monitoring layout were proposed as well.The results could provide foundations for strata control and disaster prevention in wide pillars in underground coal mines.

Mechanical behaviors of deep pillar sandwiched between strong and weak layers

A variety of coal room and pillar mining methods have been efficiently practiced at depths of up to 500 m with least strata mechanics issues.However,for the first time,this method was trialled at depths of 850 e900 m in CSM mine of Czech Republic.The rhomboid-shaped coal pillars with acute corners of 70,surrounded with 5.2 m wide and 3.5e4.5 m high mine roadways,were used.Pillars were developed in a staggered manner with their size variation in the Panel II from 83 m×25 m to 24 m×20 m(corner to corner)and Panel V from 35 m×30 m to 26 m×16 m.Coal seam inclined at 12was affected by the unusual slippery slickenside roof bands and sometimes in the floor levels with high vertical stress below strong and massive sandstone roof.In order to ensure safety,pillars in both the panels were continuously monitored using various geotechnical instruments measuring the induced stresses,side spalling and roof sagging.Both panels suffered high amounts of mining induced stress and pillar failure with side-spalling up to 5 m from all sides.Heavy fracturing of coal pillar sides was controlled by fully encapsulated steel bolts.Mining induced stress kept increasing with the progress of development of pillars and galleries.Instruments installed in the pillar failed to monitor actual induced stress due to fracturing of coal mass around it which created an apprehension of pillar failure up to its core due to high vertical mining induced stress.This risk was reduced by carrying out scientific studies including the three-dimensional numerical models calibrated with data from the instrumented pillar.An attempt has been made to study the behavior of coal pillars and their yielding characteristics at deeper cover based on field and simulation results.

Experimental study on the movement law of overlying rock non-pillar coal overhead mining

Pillarless coal mining technology is a new practical technology.Based on the compensating mechanical behavior of the Negative Poisson’s Ratio(NPR)anchor cable on the roof,the roadway was successfully retained by the top cutting and pressure relief technology.This study utilizes the Digital Speckle Monitoring(DIC monitoring),stress-strain monitoring,and infrared thermal imaging systems to conduct physical model experiment of similar materials from the displacement,stress-strain,and temperature fields to investigate in depth the fracture change law of the overlying rock.In addition,it uses FLAC3D numerical simulation to invert the surface displacement settlement.The results show that the non-pillar overhead mining under the 110 mining method has little influence on the rock crack in the middle of the coal seam,and the crack development area is mainly concentrated in the overlying rock mass of the upward coal seam.The compensatory mechanical behavior of NPR anchor cable and the dilatation characteristics of rock mass have a good effect of retaining roadway along goaf,and can also reduce surface settlement.The 110 mining method provides a scientific basis for ecological environment protection and the development of other kilometer deep soft rock high ground stress underground projects.

Study on the disaster caused by the linkage failure of the residual coal pillar and rock stratum during multiple coal seam mining:mechanism of progressive and dynamic failure

Multi-seam mining often leads to the retention of a significant number of coal pillars for purposes such as protection,safety,or water isolation.However,stress concentration beneath these residual coal pillars can significantly impact their strength and stability when mining below them,potentially leading to hydraulic support failure,surface subsidence,and rock bursting.To address this issue,the linkage between the failure and instability of residual coal pillars and rock strata during multi-seam mining is examined in this study.Key controls include residual pillar spalling,safety factor(f.),local mine stiffness(LMS),and the post-peak stiffness(k)of the residual coal pillar.Limits separating the two forms of failure,progressive versus dynamic,are defined.Progressive failure results at lower stresses when the coal pillar transitions from indefinitely stable(f,>1.5)to failing(f,<1.5)when the coal pillar can no longer remain stable for an extended duration,whereas sud-den(unstable)failure results when the strength of the pillar is further degraded and fails.The transition in mode of failure is defined by the LMS/k ratio.Failure transitions from quiescent to dynamic as LMS/k.<1,which can cause chain pillar instability propagating throughout the mine.This study provides theoretical guidance to define this limit to instability of residual coal pillars for multi-seam mining in similar mines.

The Potential of Commercial Pension Insurance to Develop into One of the Pillars of Rural Pension Insurance:A Study from the Demand Perspective

The development of a multi-pillar pension insurance system is an effective solution for an aging society.Commercial pension insurance,as the third pillar of pension insurance,is an integral part of this system in China and can play a critical and complementary role in rural areas where support for the elderly is a more pressing concern and a second pillar of pension insurance remains absent.To this end,we first elaborate on the theoretical logic that commercial pension insurance can develop into one of the pillars of rural pension insurance.We then empirically test rural residents’willingness to participate in a commercial pension insurance plan(CPIP)in a probit model with household research data from rural areas in major labor-exporting provinces,such as Sichuan and Henan so as to explore whether commercial pension insurance has the potential to become one of the pillars of rural pension insurance.Our research findings can be synthesized in three points.First,rural residents out of agricultural production for five consecutive years are more willing to participate in a CPIP than other rural residents,indicating that progress in industrialization and urbanization can significantly boost such willingness.Second,the younger rural residents are more inclined to participate in a CPIP than the older generation.Third,income increases can significantly boost rural residents’willingness to participate in a CPIP.Thus,with progress in industrialization and urbanization and an increase in rural disposable income,commercial pension insurance has a promising potential in rural areas and can hopefully develop into one of the pillars of rural pension insurance.

个人养老金税收优惠政策何以可为?——来自美国、德国和澳大利亚的经验与启示

发展个人养老金是健全养老保险体系和积极应对人口老龄化挑战的重要举措,而灵活高效的税收优惠政策则是推动个人养老金制度高质量发展的关键要素。虽然近年来我国制定了个人养老金税收优惠政策,但是仍存在诸多问题,严重掣肘个人养老金制度的高质量发展。基于文献研究法、比较分析法对美国、德国和澳大利亚等典型国家个人养老金税收优惠政策的主要实践、基本特征、实施效果以及对中国的启示等重要问题进行深入探讨。研究发现,经过数十年的积极探索,美国、德国和澳大利亚逐步建立了灵活高效的个人养老金税收优惠政策,主要体现在激励方式灵活多样、政策制定立法先行、政策调整循序渐进、关注低收入群体的需求以及鼓励以家庭为参保对象等五个方面,有效推动了其个人养老金制度的发展与成熟。不过,这些典型国家个人养老金税收优惠政策在取得瞩目成就的同时,仍然面临对低收入群体的吸引力不足等现实困境。结合典型国家的有益经验和深刻教训,对我国个人养老金税收优惠政策存在的主要问题进行剖析,并提出更具针对性的见解,认为我国个人养老金税收优惠政策应当从四个方面作出改进:一是引入多种税收优惠模式,增强政策的吸引力;二是凸显税收优惠政策的精准性,助推优惠资源向低收入群体倾斜;三是提升税收优惠政策的灵活性,鼓励个人合理配置税收优惠额度;四是税收优惠政策应支持以家庭形式参保。

松软厚煤层区段煤柱剪切滑块运动机理及协同控制技术

松软厚煤层区段煤柱高、煤壁暴露面积大,加之煤质松软、裂隙发育,强采动作用下极易造成煤柱失稳,巷道维护难度极大。以山西伏岩煤业3号煤层开采为工程背景,基于剪切滑块理论,探究采掘扰动下煤柱变形破坏机理,求解煤柱剪切滑块运动范围及应力分布规律,揭示煤柱侧帮剪切滑块运动机理,提出煤柱稳定性协同控制对策并在现场进行工程实践验证。结果表明:①采用极限平衡理论与叠加理论,确定了煤柱剪切滑块运动范围及煤柱垂直应力分布规律,阐明煤柱剪切滑块安全系数分布规律:0~1.26 m深度,煤柱上部安全系数较小;在1.26~3.95 m处,煤柱中线部分大面积安全系数较小,易受顶板来压破坏。②提出了1种以“注浆加固—锚索强化—切顶卸压”为主体的区段煤柱协同控制技术,煤柱侧裂隙较无支护条件及原支护条件分别减少62.89%和46.26%,巷道围岩完整性大幅提高,形成了强承载结构,有效控制了煤柱变形及底臌。③根据松软厚煤层区段煤柱条件,合理确定了协同控制设计参数,并对煤柱防控效果进行试验监测评估。现场试验结果表明,煤柱裂隙得到充分填充,注浆后煤体强度提高63%以上;巷道位移、锚杆索受力、离层等均在可控范围,表明协同控制技术明显提高了煤柱承载力,回采巷道围岩变形得到有效控制,为工作面安全高效开采提供了空间保障。

遗留煤柱边界下方撤面巷道合理位置确定研究

为了确定遗留煤柱边界下方撤面巷道合理布置位置,以内蒙古某矿为研究对象,基于遗留煤柱覆岩空间结构,探究应力在底板的传递规律,通过构建“上煤层遗留煤柱传递应力-下煤层巷道掘进应力”应力叠加计算模型,分析外错距离与撤面巷道围岩安全稳定之间的关系。研究结果表明:在遗留煤柱的“支撑”作用下,煤柱煤体及其上覆岩层近似成“T”型空间结构;10 m外错距离满足现场安全生产和巷道围岩控制的要求。研究结果可为相似开采条件下的巷道稳定评估和合理位置确定提供参考。

区段煤柱变形光纤光栅监测应用研究

针对近距离煤层下伏工作面过上覆遗留煤柱时,发生动静载叠加诱发强矿压显现,导致区段煤柱发生变形失稳造成人员伤亡和设备破坏。为探索基于光纤光栅实时监测区段煤柱变形发育特征,分析进、出遗留煤柱阶段矿压显现机理,将FBG、光栅应力计的光测方法相结合,结合现场实测的区段煤柱变形应力应变水平参量变化规律,研究煤柱应变空间分布规律及回采过程中工作面前方煤柱内部应变时域响应特征,验证光测方法在煤体应变水平观测的可行性。结果表明:工作面回采经过上覆遗留煤柱期间,区段煤柱顶板受集中应力影响,上部岩层块体破断并发生回转导致煤柱载荷增加,随着工作面推进覆岩断裂进一步向上传递,关键层断裂回转发生导致工作面来压,最终导致区段煤柱变形失稳。根据现场光栅应变增量幅度判断煤柱内局部变形的剧烈程度,在集中应力作用下,区段煤柱变形时发生最大应变为650×10^(-6),上覆岩层集中应力造成煤柱应变水平峰值位置为煤柱宽度11.5 m,沿煤柱宽度方向应变表现出先增加后减小然后趋于稳定的趋势,内部应变随采动过程中影响范围在5 m左右。综合研究工作面回采经过上覆遗留煤柱时应变对区段煤柱发生变形失稳的特点和规律,以及应变水平变化和煤柱物理力学性质,得到煤柱破坏的前兆特征,在外力作用下达到变形峰值前对煤柱提前进行卸压和防护的安全处理。

西山煤田岩溶陷落柱柱壁角特征研究及其意义

【意义】随着采掘向深部延伸,岩溶陷落柱已成为华北煤田矿井开采最隐蔽的致灾地质因素之一。柱壁角是描述陷落柱形态特征的重要指标之一。【方法和结果】以西山煤田上下煤层综采均切割过的265个岩溶陷落柱为数据源,通过分区、统计、函数构建、地质类比,挖掘西山煤田岩溶陷落柱柱壁角中蕴藏的地质信息,获得如下认识:(1)西山煤田陷落柱平均柱壁角为84.29°,超50%的陷落柱柱壁角在85°~90°,平均柱壁角自西北到东南逐渐增大,从82.05°增大到87.57°。(2)西山煤田陷落柱柱壁角与8号煤层揭露的陷落柱面积成反比,依据柱壁角与陷落柱面积大小关系,陷落柱划分为:充分塌陷陷落柱(90°~85°)、次充分塌陷陷落柱(<85°~81°)、不充分塌陷陷落柱(<81°);对应的2号煤层陷落柱面积分别为<556、556~1 700、>1 700 m^(2),等效半径为<13.3、13.3~23.3、>23.3 m;对应的8号煤层陷落柱面积分别为<1 250、1 250~2 750、>2 750 m^(2),半径分别为<20、20~30、>30 m。充分塌陷陷落柱一般发育有柱顶空腔,柱体结构较为松散,可导通顶板裂隙水与柱顶空腔水,以及底板承压奥灰水,是西山煤田导水陷落柱的一种重要类型。【结论】类比地质历史时期降雨量结果显示,具有“北柱南相”的西山煤田岩溶陷落柱,可能形成于气候湿热的古近纪渐新世时期,强烈的岩溶作用吸收了大气中的CO_(2),并锁定在沉积区,可能是导致全球大气CO_(2)含量急剧降低的重要原因。

多因素影响复杂空区群下残留矿柱回收模拟研究

对于有着断层切割、多矿脉等因素影响下的某钨矿Ⅰ号矿脉6~8线保安矿柱的回收问题,采用理论分析和数值计算分析了该矿山采空区的稳定性以及残留保安矿柱的回采可行性。在此基础上提出了3种残留矿柱回收方案并进行对比分析研究。研究结果表明:矿柱周边的采空区相对稳定,矿柱自身内部的应变能得到了释放,回收带来的地压灾害风险降低,其发生变位性破坏导致自身的整体刚度降低,矿柱控制地压活动的作用效应随之减弱,可以考虑对该矿柱进行安全回采。残留矿柱回采出矿后,被断层切割的残矿回采区与原左右两侧采空区之间的间柱应力集中更加明显,也出现了较大面积的剪切破坏塑性区,说明残矿回采时可能有剪切破坏的风险,而对保安矿柱两侧被断层影响的采空区进行部分充填可以有效地抑制应力集中现象,减弱边帮的松脱趋势,有效减小残矿回采区上、下盘沿断层滑移趋势,可以实现对残留保安矿柱安全经济的回收。

倾斜矿体采空区非对称顶板-矿柱结构体协同承载机理

为解决倾斜矿体回采后大倾角顶板和非对称空区可能引发的采空区支撑结构体变形及破坏失稳问题,以某石灰石矿非对称顶板-矿柱支撑结构体为研究对象,构建结构体承载力学模型,求解顶板挠曲变形值及矿柱安全系数,分析不同倾角、跨度比下顶板变形特征及矿柱失稳破坏模式,研究其协同承载机理。结果表明:顶板变形、矿柱失稳破坏模式受采空区倾角θ和跨度比λ的双重影响,顶板变形大小随着θ的增加表现为双增长率,与λ的关系伴随着θ的变化而变化。矿柱失稳破坏模式受θ的影响程度随着λ的增加而减小,当0°<θ≤30°时,矿柱主要为小偏心受压破坏;当θ=0°和30°<θ≤60°时,随着λ值的增加,矿柱破坏模式从大偏心受压破坏向小偏心受压破坏转变。顶板维系采空区稳定的能力随着θ的增加逐渐降低,矿柱维系采空区稳定的最优λ值随着θ的增加逐渐减小,矿柱约束顶板变形作用大小随着λ的增加而降低。数值模拟和工程实例验证了理论计算结果的可靠性,为地下空场法矿山安全开采提供一定的理论支撑。

宽高比对煤柱型冲击地压影响规律的实验研究

我国深部煤炭开采日趋复杂,区段煤柱在采动、构造或坚硬顶底板影响下极易诱发煤柱型冲击地压,煤柱型冲击地压的防治已成为煤矿安全高效开采的难题,研究不同宽高比条件下区段煤柱的力学性能及冲击破坏特性对煤柱型冲击地压防治具有积极意义。采用不同宽高比煤样的“岩-煤-岩”组合体进行了单轴压缩实验,通过分析煤岩组合体的冲击倾向性、动态破坏特征、分形维数和声发射特征参数等,研究了宽高比对煤柱冲击破坏的影响规律。结果发现:①煤柱的宽高比对煤岩组合体的冲击倾向性具有显著影响,宽高比不小于2∶1时,其冲击能量指数K_(E)为1.82~2.65,冲击倾向性无明显变化;小于2∶1时冲击倾向性呈先升高后降低的趋势,1∶1时K_(E)最大,达到了15.43。②随宽高比减小,煤岩组合体破坏特征依次表现为:拉压破坏—压剪破坏—拉剪破坏。煤柱宽高比为5∶1~3∶1时,煤岩组合体破坏较为缓慢;宽高比为2∶1时开始出现片状煤屑弹出,冲击破坏剧烈程度较低;宽高比为1∶1和0.75∶1时,具有明显的冲击破坏特性;宽高比为0.5∶1时,煤岩组合体整体稳定性下降,相对0.75∶1煤岩组合体煤柱破坏的剧烈程度降低。③峰后声发射能量释放率与分形维数D变化规律相似,均随宽高比减小呈先升高后降低的趋势。宽高比不小于2∶1时,煤岩组合体破坏过程中能量持续释放时间较长,煤柱破坏平缓;宽高比为1∶1时,能量释放率和D值明显增大,相较宽高比不小于2∶1煤岩组合体的能量释放率增大了约4倍,D值增大了0.18~0.23,煤柱冲击破坏最为剧烈;宽高比0.75∶1煤岩组合体能量释放率与D值分别降低了约10%和0.01,破坏剧烈程度与1∶1煤岩组合体相近;宽高比减小至0.5∶1时,相关参数的降低幅度约为0.75∶1煤岩组合体的6倍,破坏剧烈程度相对较小。研究表明:宽高比对煤柱的冲击破坏具有显著影响,整体上,煤柱冲击破坏剧烈程度随宽高比减小(5∶1~0.5∶1)呈先升高后逐渐降低的趋势;煤柱宽高比大于3∶1时,煤柱冲击危险性相对较小,煤柱宽高比为1∶1和0.75∶1时冲击危险性较大,0.5∶1次之。

特厚煤层小煤柱沿空掘巷支护技术研究

小煤柱沿空掘巷过程中易出现巷道围岩变形大、局部鼓出等现象,针对这一问题,采用理论分析、数值模拟、工程类比的方法,对巷道基本顶破断方式进行了判断,并采用数值模拟分析不同宽度下煤柱的应力及位移变化规律,初步确定了煤柱留设宽度为8 m;对比邻近矿井的沿空掘巷案例,采用工程类比法最终确定了煤柱宽度,并对巷道支护方案进行设计,现场应用效果良好。

工业广场保护煤柱开采井筒破损致因及防治技术

针对工业广场保护煤柱开采导致井筒破损的问题,以大社煤矿为工程背景,分析工广煤柱开采井筒围岩移动变形特征,揭示井筒破损致因;提出工广内后续工作面开采防治井筒破坏方案,形成相应的施工技术,并成功应用工程实践。研究表明:该矿工广内92606工作面邻近副井,开采引发的井筒竖向附加力是井筒破坏的致因;如不提前采取防治措施,后续92606外工作面开采,将导致副井井筒发生二次破坏;研究提出的不停产单卸压槽防治方案,具有不影响矿井生产、卸压率高、施工简单、成本低等优点。采用壁后注浆、开切卸压槽、架设密集井圈等技术,顺利完成了该矿不停产防治副井井筒破损工程。监测表明,该井筒竖向和环向应力,均小于井壁极限.承载力,处于安全状态,运行良好,达到了预期效果。