Stability of inner dump slope under coal pillar support:case study in an open‑pit coal mine

The stability of an inner dump slope was investigated under the efect of coal pillar support considering the development position of dumping.Based on the instability mechanism and load distribution characteristics of the supporting coal pillar,the three-dimensional mechanical efects of the supporting coal pillar are characterized.Using the two-dimensional equivalent principle and the residual thrust method,the stability of the inner dump slope was analyzed under the efect of pillar support at diferent dump development positions.The quantitative efects of various factors on the inner dump slope stability were revealed,and the coal pillar shape parameters were optimized through numerical simulations.The results indicate that the slope stability coefcient is linearly related to the top width and height of the coal pillar,slope angle,and base inclination angle,and has an exponential relation with the coal pillar strike length and slope height increment.There are quadratic and absolute value relations with the coal pillar outer and the inner bottom angle,respectively.The top width of the coal pillar in the inner dump of Shengli East No.2 open-pit coal mine should be at a level of+824 m,and the optimal top width and height are 15 and 36.7 m,respectively.The instability mechanism of the supporting and retaining coal pillar obtained by numerical simulations and the stability of the inner dump are in good agreement with the theoretical analysis.Our results provide a theoretical basis for the design,treatment,and safe implementation of similar open-pit mine slope engineering.

Stability of coal pillar in gob-side entry driving under unstable overlying strata and its coupling support control technique

Considering the situation that it is difficult to control the stability of narrow coal pillar in gob-side entry driving under unstable overlying strata, the finite difference numerical simulation method was adopted to analyze the inner stress distribution and its evolution regularity, as well as the deformation characteristics of narrow coal pillar in gob-side entry driving, in the whole process from entry driving of last working face to the present working face mining. A new method of narrow coal pillar control based on the triune coupling support technique (TCST), which includes that high-strength prestressed thread steel bolt is used to strain the coal on the goaf side, and that short bolt to control the integrity of global displacement zone in coal pillar on the entry side, and that long grouting cable to fix anchor point to constrain the bed separation between global displacement zone and fixed zone, is thereby generated and applied to the field production. The result indicates that after entry excavating along the gob under unstable overlying strata, the supporting structure left on the gob side of narrow coal pillar is basically invalid to maintain the coal-pillar stability, and the large deformation of the pillar on the gob side is evident. Except for the significant dynamic pressure appearing in the coal mining of last working face and overlying strata stabilizing process, the stress variation inside the coal pillar in other stages are rather steady, however, the stress expansion is obvious and the coal pillar continues to deform. Once the gob-side entry driving is completed, a global displacement zone on the entry side appears in the shallow part of the pillar, whereas, a relatively steady fixed zone staying almost still in gob-side entry driving and present working face mining is found in the deep part of the pillar. The application of TCST can not only avoid the failure of pillar supporting structure, but exert the supporting capacity of the bolting structure left in the pillar of last sublevel entry, thus to jointly maintain the stability of coal pillar.

Layout and support technology of entry for pillar face

In order to improve the recovery rate of coal, some mines have begun to recover the residual protective pillars in the form of short wall faces. However, it is difficult to control stability of the haulage entry and the ventilating entry under the mining influences of the pillar face and the two side faces. Thus the 4311 face, which was designed to recover the 57 m wide residual protective pillar in Guojiashan Coal Mine,was taken as engineering background. Distribution law of stress and plastic zone in the residual protective pillar was analyzed using the numerical simulation. Then the gob-side entry driving technology was proposed to layout the entries for the pillar face. Based on the analysis of stress distribution and deformation characteristics of surrounding rocks in gob-side entry driving with different width of narrow pillars, the width of the narrow pillar of the entries in the 4311 face was decided to be 4 m. In order to control stability of the gob-side entry driving, the mechanical model of the main roof was established and deformation characteristic of surrounding rock was analyzed. Then the bolt support technology with high strength and high pre-tightening force was proposed for entry support. Especially, the hydraulic expansion bolts were used to support the narrow pillar rib. The engineering results show that the width of the narrow pillar is reasonable and the entry support technology is effective. The research achievement can provide some references to pillar recovery for other coal mines.

Preventing roof fall fatalities during pillar recovery:A ground control success story

For decades, pillar recovery accounted for a quarter of all roof fall fatalities in underground coal mines.Studies showed that a miner on a pillar recovery section was at least three times more likely to be killed by a roof fall than other coal miners. Since 2007, however, there has been just one fatal roof fall on a pillar line. This paper describes the process that resulted in this historic achievement. It covers both the key research findings and the ways in which those insights, beginning in the early 2000 s, were implemented in mining practice. One key finding was that safe pillar recovery requires both global and local stability.Global stability is addressed primarily through proper pillar design, and became a major focus after the2007 Crandall Canyon mine disaster. But the most significant improvements resulted from detailed studies that showed that local stability, defined as roof control in the immediate work area, could be achieved with three interventions:(1) leaving an engineered final stump, rather than extracting the entire pillar,(2) enhancing roof bolt support, particularly in intersections, and(3) increasing the use of mobile roof supports(MRS). A final component was an emphasis on better management of pillar recovery operations.This included a focus on worker positioning, as well as on the pillar and lift sequences, MRS operations,and hazard identification. As retreat mines have incorporated these elements into their roof control plans,it has become clear that pillar recovery is not ‘‘inherently unsafe." The paper concludes with a discussion of the challenges that remain, including the problems of rib falls and coal bursts.

Development of a spring analogue approach for the study of pillars and shafts

In civil and mining operations that involve ground excavation and support, the loads are distributed between the ground and support depending on their relative stiffness. This paper presents the development of conceptual single-degree-of-freedom models, which are used to derive equations for estimating displacements and stresses for ground-support interaction problems encountered in pillars in room-andpillar mining(natural support system), and liners for circular vertical shafts(artificial support systems).For pillar assessment, mine-pillar interaction curves can be constructed using a double spring analogy.Additionally, the effectiveness of different support systems can be evaluated depending on their effect upon the mine-pillar system. For shaft design, an initial estimation of the required lining strength and thickness can be readily made based on a double ring analogue. For both problems, the results from the proposed approach compare well with those obtained by finite element numerical simulations.

Countermeasure Method for Stope Instability in Crown Pillar Area of Cut and Fill Underground Mine

Maintaining stability as well as optimizing recovery of crown pillar, a pillar separating surface area with the uppermost stope in overhand cut and fill underground mining method, is important. Failures in stope may lead to crown pillar failures and cause surface subsidence. Increasing crown pillar thickness will increase crown pillar stability yet reduce mining recovery because part of crown pillar is formed by ore body. Preventing stope failure is the key to maintain stability and optimize recovery of crown pillar. Therefore, it is important to study countermeasure method for stope failure especially in crown pillar area. An attempt has been made to investigate the effectiveness of various countermeasures for stope failure in crown pillar area by means of parametric study. The result shows active type support system is effective for supporting stope in high vertical stress condition while the passive one needs to be installed if the stope is opened in high horizontal stress condition. In general, more supporting capacity from both type support systems is needed if the stope is opened in more severe geological condition. Another countermeasures, sill pillar and surface pile, are introduced for stope instability in crown pillar and non-crown pillar area. Sill pillar is an abandoned slice of unstable stope based on stability analysis. Sill pillar is very effective to stabilize stope both in crown pillar and non-crown pillar area, especially for stope in high horizontal stress condition. Sill pillar application in model with stress ratio 2 can optimize 20 meter thickness of crown pillar into 5 meter. Another proposed countermeasure is surface pile. Surface pile can be installed from the surface to improve stability of crown pillar and stope. The most effective use of surface pile is found in simulation of model with stress ratio 0.75 where surface pile can optimize 15 meter thickness of crown pillar into 5 meter.

Wide pillar roadway retained in the deep high gas coal seam

According to the geological and mining conditions of deep high gas coal seam,this paper established the mechanical model of stope surrounding rock,and analyzed the stress distribution and deformation failure mechanism of working face and coal pillar.The research determined the arrangement mode that adjacent working faces retain wide pillar,and the reasonable support method of roadway that the combined support of roof and grouting combined together.The reasonable time of reinforced roadway was determined.Through analyzing the mechanical model of the ways of roadway supporting,this research drew the conclusions as follows:the combined support of roof and working slope improved the support strength and range of surrounding rock,optimized the support by adjusting the angle of anchor,and reached the support requirements by using cement grouting in working slope and chemical grout in roof.The technology was applied in 15104 working face of Baoan Mine,and obtained good results.

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。

综采面沿空巷道超前动压区煤柱失稳效应与锚注加固技术

为探究综采面沿空巷道超前动压区煤柱对巷道围岩整体稳定的影响规律,综合采用数值模拟、工程应用等方法,建立沿空巷道超前巷道数值分析模型,研究综采面回采期间不同煤柱宽度下沿空巷道围岩力学和变形响应特征。研究结果表明:护巷煤柱宽度小于5 m时,工作面帮为采动应力主要承载结构,其内部应力及变形均大于煤柱帮,此时工作面帮应作为超前动压区重点加固对象,随着护巷煤柱宽度增加,煤柱承载应力逐渐增加、变形增大,护巷煤柱宽度增加至5 m以上时,煤柱承载应力显著增加,采动应力由沿空巷道两帮围岩共同承载,超前动压区应同时加强两帮支护,基于此开发超前动压区沿空巷道锚注加固技术,并进行工程应用。研究结果可为平顶山矿区类似条件沿空巷道超前控制提供一定参考。

错层位外错式巷道位置选择及联合支护研究

针对新巨龙煤矿1301综放工作面区段间留设煤柱尺寸较大造成的资源浪费和回采巷道支护困难等问题,本文提出采用错层位外错式巷道布置方案,建立错层位非常规煤柱力学模型,利用极限平衡理论分析了非常规煤柱应力环境和极限平衡区特征;考虑不同错距下沿底巷道所处应力环境及区段煤柱弹性应变能密度分布特征,确定下区段沿底巷道合理错距为3.0 m;同时引入区段间相邻巷道联合支护方案,对实际地质条件下接续工作面回采阶段区段间相邻巷道联合支护方案和传统支护方案进行模拟验证。结果表明:区段间相邻巷道联合支护方案优于传统支护方案,峰值应力由80 MPa降至64 MPa,降低率为20%,表明其对巷道围岩控制更为有效;区段煤柱单位留设面积为111.5 m^(2),相较于传统支护方案区段煤柱的170 m^(2),降低率为34.4%。研究结果对减少区段煤柱留设尺寸和提高煤炭回采率起到积极的推动作用。

深部特厚煤层综放沿空掘巷煤柱优化及巷道支护

为研究深部大采高综放工作面窄煤柱沿空掘巷巷道矿压控制问题,以国能宁煤集团枣泉煤矿2^(-2)特厚煤层130203大采高综放工作面回风巷道为背景,基于实用矿山压力理论,建立了巷道围岩内、外应力场动态结构力学模型,运用理论计算和数值计算针对不同尺寸煤柱煤体应力对比分析,将原留设15 m护巷煤柱缩小至5 m进行了煤柱优化。结果表明:在稳定的内应力场掘巷有利于巷道的稳定性,避免了顶板事故及冲击地压相关灾害的发生,现场5 m小煤柱护巷工程应用中,130203回风巷道小煤柱侧变形量为1050 mm,实体煤帮变形量为400 mm,两帮呈现不对称性变形,底板局部底鼓量为1400 mm;深部特厚煤层综放开采沿空掘巷采用5 m小煤柱护巷方案设计正确,极大改善了巷道围岩的应力环境,整体设计满足生产要求,现场应用良好。130203工作面小煤柱沿空掘巷技术成功应用,为矿井开采提供了可靠的科学依据。

预掘双回撤通道稳定性机理及控制技术研究

为解决预掘双回撤通道贯通时回撤通道围岩稳定性问题,通过理论分析、数值模拟和现场实测相结合的方法,研究分析了回撤通道贯通时围岩破坏机理、通道间合理煤柱尺寸、工作面贯通不同位置时围岩塑性区分布与应力分布规律。结果表明:主、辅回撤通道间煤柱理论宽度为20 m,此时煤柱内部应力分布呈现双峰状,辅助回撤通道围岩应力较小;20 m煤柱条件下,工作面进入末采期,主回撤通道围岩逐渐破坏,辅助回撤通道围岩塑性区范围较小,因此确定主、辅回撤通道间煤柱宽度为20 m。工作面末采期主回撤通道采用垛式支架加强支护,现场实测主回撤通道帮部最大变形量180 mm,巷道完整性较好。

近距离煤层多次采动影响巷道围岩破坏特征与控制

针对隆德煤矿近距离煤层上下同采工作面巷道围岩稳定性控制问题,采用现场实测和理论分析方法,对多次采动影响下巷道支护体受力特征和煤柱应力演化特征进行研究。结果表明,巷道锚杆/索受力经历7个变化阶段,包括采动影响前初始稳定阶段、单工作面超前影响阶段、双工作面超前影响阶段、采动卸压区快速升高阶段、采动应力恢复区慢速升高阶段、二次稳定阶段和双工作面开采扰动升高阶段;煤柱采动应力演化经历5个阶段,包括采动影响前初始稳定阶段、单工作面超前影响区缓慢上升阶段、采动卸压区快速上升阶段、采空区压实自由演化阶段和双工作面开采扰动升高阶段。随着钻孔应力计安装深度增加,煤柱应力呈现先升高后降低趋势,煤柱浅部3 m左右进入塑性状态,承载能力降低;基于上述观测结果,对新掘巷道支护参数进行优化,在保证围岩长期稳定性的同时还可以降低支护费用,实测结果表明,支护参数优化后巷道表面位移量在工程允许范围内,巷道围岩裂隙发育程度较低。

煤柱承载计算方法改进及尺寸优化

以禾草沟一矿为工程背景,通过监测相邻工作面区段煤柱侧向支承应力分布、内应力场分布范围,分析了工作面采动应力影响范围及程度,研究了不同区段煤柱宽度下采空区应力分布特征、区段煤柱载荷分布形态及演化特征。为15214工作面与15216工作面区段护巷煤柱留设提供依据。综合理论分析,得到结论:改进煤柱支承能力计算公式,并考虑煤柱尺寸效应对煤柱尺寸进行优化,将15214工作面与15216工作面之间的区段煤柱从之前的20 m调整到5 m。

厚煤层区段煤柱合理留设宽度及支护参数优化研究

采动影响下厚煤层区段煤柱的合理留设是煤炭高效安全回采的重要因素。针对该问题依托中能煤矿3号煤2309工作面回风巷区段煤柱留设进行研究。根据围岩极限平衡理论计算出煤柱合理宽度为8m,结合Flac3D数值计算分析不同宽度煤柱垂直应力及塑性区,验证煤柱留设宽度不应小于8m;针对留设煤柱巷道应用差异化支护方法,对煤柱侧采用帮部3道锚索补强的方法进行围岩加固;针对浸泡煤柱、漏风、有害气体涌入等隐患采取煤柱局部注浆和表面喷浆的方式控制。结合矿压监测反馈表明煤柱留设宽度合理,支护效果良好,为类似厚煤层区段煤柱留设提供技术参考。

注浆锚索在综采工作面超前支护中的应用研究

霍州煤电木瓜矿为提高综采工作面回采巷道围岩有效控制,提出将注浆锚索应用到回采巷道超前支护中,并以该矿10-206工作面辅运顺槽为研究对象,对注浆锚索布置方案及现场应用效果等进行分析。现场应用后,10-206工作面辅运顺槽超前支护段围岩变形量较小、顶板始终保持稳定,同时取消超前单体支柱后,工作人员劳动强度明显降低,巷道运输及通风断面明显增大,为采面煤炭高效开采创造相对良好条件,同时也为矿井地质条件相类似注浆锚索的应用提供参考与借鉴。

浅埋煤层沿空掘巷小煤柱留设宽度及支护技术研究

为研究浅埋煤层区段留设小煤柱宽度和沿空巷道支护技术,以微子镇矿15103工作面小煤柱沿空掘巷为研究对象,通过理论计算和数值模拟分析确定了小煤柱合理宽度为7 m,提出了掘进期间采用锚杆+锚索联合支护、回采期间采用超前支架加强支护的支护方案。该方案对15103工作面沿空巷道变形有较好的控制作用,取得了显著的效益。

围岩加强支护留窄煤柱护巷的可行性研究

为了减少煤矿井下资源浪费现象的发生,研究了留设不同宽度保护煤柱时,围岩塑性区及垂直应力在施工“支护-卸压-砌墙”协同控制技术前后的数值模拟对比分析。数值模拟结果表明:未采取围岩加强支护措施时,随着停采线与回风大巷之间距离的减小,煤柱垂直应力峰值呈先增大后减小的趋势,且回风大巷围岩破坏变形严重;施工“支护-卸压-砌墙”协同控制技术后,随着保护煤柱的回采,煤柱与回风大巷围岩的塑性形变区域面积占比都显著减小,且回风大巷的垂直应力峰值平均减小了25.32%,应力集中系数平均减小了27.03%;在保证煤柱及大巷围岩稳定的前提下,可适当的缩减保护煤柱的宽度,以减少煤炭资源的浪费,并可为煤矿带来较大的经济效益。

上社煤矿双巷掘进巷道布置及支护设计研究

以上社煤矿9217双巷掘进工作面为研究对象,采用UDEC数值模型分析了双巷掘进阶段及首工作面回采过程中不同煤柱尺寸下裂隙扩展演化及围岩变形特征。确定了合理的煤柱宽度为12 m,并设计了9217回风顺槽锚索支护参数。将方案成功应用于上社煤矿的工程实践中,取得了理想的围岩控制效果,显著提高了开采效率,同时缓解了开采接替紧张的问题。

红沙泉露天矿端帮采煤机开采技术研究

为了提高红沙泉露天矿端帮煤炭资源回收效率,减少端帮压覆资源浪费。以红沙泉露天煤矿首采区西端帮为研究对象,结合端帮采煤机原理研究了支撑煤柱宽度和隔离煤柱的宽度,探究了自然工况条件下的西端帮的边坡稳定性和在端帮采煤机开采留设煤柱的条件下边坡稳定性。结果表明:通过Mark-Bieniawsk给出的计算公式得出支撑煤柱的宽度为5.5 m,隔离煤柱的宽度为27.3 m;西端帮在自然工况条件下的稳定系数为1.957,在使用端帮采煤机开挖采硐后的边坡稳定系数为1.805,但均符合露天矿设计规范的要求。红沙泉露天煤矿具有使用端帮采煤机的条件,能够解决端帮压覆煤回采的问题。