Surrounding rock control of gob-side entry driving with narrow coal pillar and roadway side sealing technology in Yangliu Coal Mine

Gob-side entry driving can increase coal recovery ratio, and it is implied in many coal mines. Based on geological condition of 10416 working face tailentry in Yangliu Coal Mine, the surrounding rock deformation characteristics of gob-side entry driving with narrow coal pillar is analysed, reasonable size of coal pillar and reasonable roadway excavation time after mining are achieved. Surrounding rock control technology and effective roadway side sealing technology are proposed and are taken into field practice. The results showed that a safer and more efficient mining of working face can be achieved. In addition, results of this paper also have important theoretical significance and valuable reference for surrounding rock control technology of gob-side entry driving with narrow coal pillar under special geological condition.

Failure laws of narrow pillar and asymmetric control technique of gob-side entry driving in island coal face

In allusion to the problems of complex stress distribution in the surrounding rock and deformation failure laws, as well as the difficulty in roadway supporting of the gob-side entry driving in the island coal face, 2107 face in Chengjiao Colliery is researched as an engineering case. Through physical mechanical test of rock, theoretical and numerical simulation analyses of rock, the analysis model of the roadway overlying strata structure was established, and its parameters quantified. To reveal the deformation law of the surrounding rock, the stability of the overlying strata structure was studied before, during and after the roadway driving. According to the field conditions, the stress distribution in coal pillar was quantified, and the surrounding rock deformation feature studied with different widths of the pillars in gob-side entry driving. Finally, the pillar width of 4 m was considered as the most reasonable. The research results show that there is great difference in support conditions among roadway roof, entity coal side and narrow pillar side. Besides, the asymmetric control technique for support of the surrounding rock was proposed. The asymmetric control technique was proved to be reasonable by field monitoring, support by bolt-net, steel ladder and steel wire truss used in narrow pillar side.

Patterns and security technologies for co-extraction of coal and gas in deep mines without entry pillars

Retaining gob-side entryways and the stability of gas drainage boreholes are two essential techniques in the co-extraction of coal and gas without entry pillars （CECGWEP）. However, retained entryways located in deep coal mines are hard to maintain, especially for constructing boreholes in confined spaces, owing to major deformations. Consequently, it is difficult to drill boreholes and maintain their stability, which therefore cannot guarantee the effectiveness of gas drainage. This paper presents three measures for conducting CECGWEP in deep mines on the basis of effective space in retained entryways for gas drainage, They are combinations of retaining roadways and face-lagging inclined boreholes, retaining roadways and face-advancing inclined boreholes, and retaining roadways and high return airway inclined boreholes. Several essential techniques are suggested to improve the maintenance of retained entryways and the stabilization of boreholes. For the particular cases considered in this study, two field trials have verified the latter two measures from the results obtained from the faces 1111（1） and 11112（1） in the Zhuji Mine. The results indicate that these models can effectively solve the problems in deep mines. The maximum gas drainage flow for a single hole can reach 8.1 m^3/min and the effective drainage distance can be extended up to 150 m or more.

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.

Influence of abnormal stress under a residual bearing coal pillar on the stability of a mine entry

Mine entries close to residual bearing coal pillars(RBCPs) will suffer large deformation that may cause rock burst. To better understand the deformation mechanism and develop safe and practical guidelines for entry design, most studies focus on the absolute size of the stress field in and around the pillar. In this paper, we present a new approach to analyze the abnormal stress field close to a RBCP that uses the stress concentration coefficient(SCC), stress gradient(SG), and coefficient of lateral pressure(CLP) to describe the stress state induced by the RBCP. Based on elastic theory and a mathematical model for the abutment stress in the RBCP, an analytical solution for the abnormal stress in the strata below the RBCP was derived and the characteristics of the abnormal stress for a case study of a coal mine in China were analyzed. The results show that the abnormal stress field around the pillar is characterized by four distinct zones: a zone of high SCC, high SG, and CLP less than 1, a zone of high SCC, low SG, and CLP less than 1, a zone of low SCC, SG close to 0, and CLP greater than 1, and a zone of SCC close to 1, SC close to 0, and CLP close to 1. Based on this zoning pattern, a numerical model was established to study the combined effects of the abnormal stress on the stability of the entry. The most stable zone was determined based on a model of the Xinrui coal mine and verified by field measurements at the mine. Our conclusions can be used as guidelines for designing safe entry layouts in similar geological and mining settings.

Top-coal deformation control of gob-side entry with narrow pillars and its application for fully mechanized mining face

A mechanical model to control the top-coal deformation is established in accordance with the structural characters of the gob-side entry surrounding rock for the fully-mechanic top-coal caving; the analytical solution of top coal roof-sag curve is deduced with Winkler elastic foundation beam model. By means of a calculating and analytic program, the top coal roof-sag values are calculated under the conditions of different supporting intensities, widths of narrow pillars and stiffness of top coal; meanwhile, the relationship between the roof-sag values and supporting intensity, width of narrow pillars and stiffness of top coal is analyzed as well. With the actual situation of the gob-side entry taken into consideration, the parameters of top-coal control are determined and a supporting plan is proposed for the top-coal control,which is proved to be reliable and effective by on-site verification. Some theoretical guidance and advice are put forward for the top-coal deformation control in gob-side entry for fully mechanized top-coal caving face.

User-friendly finite element design of main entries, barrier pillars,and bleeder entries

This contribution describes development and application of a user-friendly finite element program,UT3PC, to address three important problems in underground coal mine design:(1) safety of main entries,(2) barrier pillar size needed for entry protection, and(3) safety of bleeder entries during the advance of an adjacent longwall panel.While the finite element method is by far the most popular engineering design tool of the digital age, widespread use by the mining community has been impeded by the relatively high cost of and the need for lengthy specialized training in numerical methods.Implementation of UT3PC overcomes these impediments in three easy steps.First, a material properties file is prepared for the considered site.Next, mesh generation is automatic through an interactive process.A third and last step is simply execution of the program.Examples using data from several western coal mines illustrate the ease of using the application for analysis of main entries, barrier pillars, and bleeder entry safety.

深埋倾斜特厚煤层窄煤柱护巷机理与围岩控制

我国中东部地区采深大、巷道变形和冲击风险大,窄煤柱沿空掘巷技术可改善巷道围岩环境。为掌握窄煤柱护巷机理并形成针对性围岩控制技术体系,以800 m埋深倾斜特厚煤层3 m窄煤柱沿空掘巷为背景,开展了理论分析、现场实测及数值模拟研究,结果表明:①该巷围岩破碎程度及变形煤柱侧比实体煤侧严重,煤柱破碎程度及变形采空区侧比巷道侧大,尽管埋深大,但已稳定采空区承担较大覆岩载荷,高应力已充分向深部岩体分流;②巷道变形非对称,实体煤侧顶板下沉量比煤柱侧大,巷帮以浅部变形为主,煤柱帮上部和实体煤帮中部变形较大;③采空区是掘巷卸荷后主要的形变通道,利于形变能向采空区缓释、降低冲击风险;④卸压区形状由掘巷前三角形扩展为掘巷后平行四边形,掘巷后应力集中区转移至实体煤帮右上方实体煤岩体中;⑤窄煤柱一次和二次剪切破坏的交界面及掘巷右上方实体高应力区为围岩关键控制区,据此提出基于煤柱多重塑性破坏区发育规律的煤柱加固和高应力区精准卸压联合的围岩控制技术体系。研究可为邻近工作面以及其他类似深埋倾斜特厚煤层开采提供理论支撑和科学依据。

特厚煤层沿空掘巷围岩支卸协同控制技术

针对特厚煤层小煤柱沿空掘巷大范围塑性全煤巷道锚网索的支护难题,以塔山煤矿8204-2小煤柱工作面为工程背景,采用现场实测、理论分析等方法,揭示了锚杆、锚索对沿空大范围塑性全煤巷道的支护机理。锚杆支护主要作用于浅部二次破碎区煤体,形成浅部连续承载结构;锚索主要作用于深部处于三向受力状态的稳定煤体,形成更大范围的连续稳定承载结构;进一步明确了锚杆、锚索有效长度的计算方法,形成了以高预紧力、高强“锚-网-索”支护为基础,以坚硬顶板井下磨料水射流切顶卸压、巷帮大直径钻孔卸压、底板卸压槽卸压为辅的“支卸协同”小煤柱沿空巷道围岩控制技术体系。工程应用结果表明,试验巷道围岩最大变形量小于700 mm,能够满足使用要求。

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。

综放面“双硬”煤层临空煤柱宽度及承载强度校核

具有“双硬”特征煤层的工作面其护巷煤柱的极限尺寸确定与常规工作面有所不同。以榆树岭煤矿505工作面沿空掘进巷道为背景,首先测试了煤岩样的力学性质和不同高径比煤样的抗压强度,得到了不同高径比煤样峰值强度曲线;其次分析了沿空掘巷覆岩结构模型,建立了沿空掘巷护巷煤柱顶板力学模型,得到了不同宽度煤柱所受的载荷应力;建立了不同高宽比煤柱的数值模型,得到了不同高宽比煤柱的极限强度校核公式;最后通过对比不同宽度煤柱所受的载荷应力和极限强度,得出4m宽度的煤柱即可满足支护要求,并在此基础上提出了沿空掘进巷道支护工艺。现场监测结果表明,煤柱宽度为4m时,巷道整体变形量较小,巷道稳定性得到有效维护。研究结果可为小煤柱护巷宽度的确定提供参考。

窄煤柱沿空掘巷非对称支护力学特征与支护参数研究

为了研究窄煤柱沿空掘巷非对称支护下围岩变形与应力分布特征,采用理论分析方法,研究窄煤柱沿空巷道对称支护与非对称支护力学机理;基于马道头煤矿现场工程实践,采用数值模拟与工程效验方法,研究非对称支护下巷道围岩力学特征与稳定性。理论分析结果表明,非对称支护可有效降低巷道顶板弯矩,减小巷道顶底板与两帮变形量。模拟结果表明,煤柱内部压应力增高区与弹性核区保障了煤柱承载性能。现场实测结果表明,采用“锚索+槽型钢”非对称支护,巷道顶板、窄煤柱侧巷帮与实体煤侧巷帮最大变形量分别为100、79、62 mm,巷道松动圈与裂隙发育处于中等水平。

强动压松软煤体条件下沿空掘巷护巷煤柱尺寸研究

针对强动压松软煤体条件下综采工作面沿空巷道围岩变形量大、稳定性差的难题,本文以赵庄煤矿5328工作面为研究背景,通过理论计算,得到了沿空掘巷煤柱尺寸的留设范围;然后通过建立数值模拟模型对多种宽度煤柱的围岩应力和塑性区进行分析,确定煤柱的合理尺寸为8 m。现场矿压监测结果表明,留设宽度为8 m的煤柱可以满足工作面安全生产要求。

近距离煤层沿空掘巷围岩稳定性分析

合理的煤柱留设宽度及巷道布置错距不仅能保证煤炭的安全生产,还能提高煤炭资源的产出率,降低巷道支护的难度。以色连二矿近距离煤层群12409工作面为研究背景,采用理论分析得出沿空掘巷煤柱留设宽度,通过数值模拟研究了留设8 m小煤柱时回采巷道的稳定性,并进行现场工业性试验,监测回采期间巷道矿压显现规律。研究结果表明:①基于极限平衡理论及工程经验设计留设8 m小煤柱;②留设8 m小煤柱,测点超前工作面17 m时,煤柱内3.5~5.9 m分布式光纤应变值为-1 470~-7 268,表明煤柱内形成承载区域,利于巷道围岩控制;③回采期间,巷道顶底板及两帮的最大移近量分别为250、123 mm,在可控范围内,保证了矿井安全高效生产。

浅埋煤层留小煤柱沿空掘巷技术研究与应用

在凤红煤业151302工作面采用沿空掘巷工艺技术,通过理论计算并结合数值模拟,综合分析确定了小煤柱的合理尺寸为5.0 m,同时优化了小煤柱巷道支护参数方案。工程应用结果表明:采用留小煤柱沿空掘巷技术,锚杆索受力远低于破断载荷;巷道顶板下沉位移在200 mm之内,回采帮内位移位小于200 mm,煤柱帮内位移在150 mm之内,巷道围岩和小煤柱皆处于稳定结构状况,整体围岩控制效果良好。

沿空留巷巷道煤体注浆补强支护技术研究

为解决厚煤层工作面沿空留巷煤柱因受动载载荷多次加卸载过程造成的巷道围岩破碎、煤柱承压大、支护难度大、巷道易变形等问题,以S1205工作面为工程背景,采用理论分析方法对巷道围岩受力变化和破坏特征进行了分析,据此提出巷道围岩注浆补强支护技术,通过数值模拟和现场实测,结果表明,该技术能够有效提高巷道围岩整体稳定性和承压能力,与采取措施前相对比,应用该技术后巷道围岩塑性区范围减小了43.1%,变形速率减小了53.8%,巷道围岩变形量得到有效控制,为类似条件下沿空留巷支护提供一定的技术参考。

同忻煤矿窄煤柱宽度留设及围岩控制实践

针对特厚煤层综放开采沿空掘巷时,留设宽煤柱护巷造成煤炭资源丢失严重,以及围岩变形量大、煤壁片帮等问题,以同忻煤矿8311工作面5311回风巷为工程背景,采用理论分析、数值模拟和现场观测相结合的方法,对其沿空掘巷护巷煤柱合理宽度的留设进行了分析。研究表明,理论分析得知留设煤柱宽度为6 m左右时可确保5311回风巷位于沿空边缘煤体支承压力降低区和煤体应力屈服区,有利于巷道围岩的稳定。基于3DEC数值模拟分析,得到留设6 m煤柱5311回风巷的稳定性以及8311工作面回采后沿空掘巷超前段顶板、实体煤帮、煤柱内围岩应力分布和塑性区演化特征。经现场应用,验证了综放开采留设窄煤柱掘巷技术的优越性和可靠性。

集贤煤矿切顶留巷关键参数及留巷稳定性分析

针对双鸭山集贤煤矿东二采区16#右三工作面切顶留巷难题,建立了切顶留巷围岩力学模型,给出了切顶高度、切顶角度等关键参数理论计算式;分析了切顶参数(切顶高度、切顶角度)对留巷围岩应力分布及变形特征影响规律。模拟结果表明:切顶高度越大,卸压效果越好;切顶角度增大,实体煤侧应力呈现增大趋势,同时也为矸石垮落创造一定条件。相似模拟结果表明:当煤层开采至一定距离时,采空区上位岩层同期垮落,切缝范围岩体和垮落岩体形成铰接,即巷旁充填基本完成,留巷上方形成“低位悬臂梁+高位铰接岩梁”结构。实践结果表明:切顶高度8.0 m(即切断2.39 m的中砂岩),切顶角度10°,切顶钻孔排距600 mm,距工作面60 m左右时,顶板下沉量为168 mm,实体煤帮移近量212 mm,矸石帮变形量几乎为0,底鼓量120 mm。

大采高工作面小煤柱沿空掘巷煤柱宽度优化及围岩控制技术研究

以马泰壕矿3103辅运顺槽为研究对象,采用现场监测、内外应力场和极限平衡区理论、数值模拟等相结合方法,对大采高工作面小煤柱沿空掘巷煤柱宽度进行研究。研究表明:现场监测煤柱支承压力分布规律,最终初步设计沿空掘巷留设小煤柱宽度为6~10 m;理论计算显示,小煤柱宽度合理范围为6.0~8.1 m;数值模拟表明,煤柱宽度大于6 m时,煤柱具有一定承载能力,煤柱上方和巷道顶板出现核心弹性区,有利于发挥锚固作用,煤柱宽度越大,应力集中现象越明显,综合考虑小煤柱宽度为6 m。基于此,提出了“锚网索支护+卸压+滞后沿空侧注浆加固+回采期间周期来压附近补强支护”围岩控制技术,现场应用效果良好。

厚煤层小煤柱沿空掘巷围岩控制技术研究

程庄煤矿15#煤层原采用25~30 m大煤柱护巷,导致临空巷道动压大、维护困难,且资源浪费较严重。以15308综放工作面为工程背景,通过使用理论计算、工程类比等手段,确定了最佳小煤柱护巷尺寸为6 m,同时采用爆破切顶、优化巷道支护参数,并配合注浆加固、喷浆、卸压槽等诸多措施,实现了小煤柱的沿空掘巷,既降低了临空巷道动压对巷道的影响,又减少了煤炭资源的浪费,延长了矿井服务年限。