Support-surrounding rock relationship and top-coal movement laws in large dip angle fully-mechanized caving face

When mining the fully-mechanized longwall caving face along strike, the unstable equipment, the low top-coal recovery ratio and the difficulty in controlling surrounding rock may occur due to large dip angle. Considering the effects of strike angle on support stability, the ‘‘support-surrounding rock"mechanical models of support topple and support slip were established in this paper. On the basis, the influencing factors of support stability were analyzed and the technical measures of controlling support and surrounding rock stability were put forward. Then the loose particles simulation experiment was conducted to analyze the impacts of caving directions and methods on the top-coal recovery in large dip angle fully-mechanized caving face. Finally, the ‘‘upward sequence and double-openings doublerounds" caving technology was determined. The research results are of great scientific significance and practical values to improve large dip thick seam mining technology.

Characteristics of Gas Emission at Super-Length Fully-Mechanized Top Coal Caving Face

Characteristics of gas emission at the K8206 working face in the Third mine of the Yangquan Coal Group were investigated. The effects of strata movement,advancing velocity of working face,production capacity of working face and gas extraction capability of strike high-level entry on gas emission at K8206 working face were analyzed. A regression equation,reflecting the relationship between relative gas emission rate and the production capacity of work-ing faces,was established. Another regression equation showing the relationship between the gas emission rate from adjacent layers when the working face was advancing for one metre and advancing velocity was derived. It can be con-cluded that,1) the amount of gas emitted at the K8206 working face is far greater than that of ordinary top coal caving faces with a dip length of 180-190 m; 2) the dynamic process of gas emission from adjacent layers during the initial mining stage is controlled by the movement of key strata; 3) the amount of gas emitted that needs to be forced out by air is greatly affected by the capability of gas extraction; 4) when the advancing velocity is between 3.5-5.5 m/d or when the output is up to 8-12 kt/d,the gas emission from adjacent layers is almost constant.

Patterns governing distribution of surrounding-rock stress and strata behaviors of fully-mechanized caving faces

By employing numerical modeling, similar material simulation and comprehen-sive field observation, investigations were made and patterns were obtained governing surrounding-rock stress distribution and strata behaviors. It shows that patterns governing displacement of FMC roadway surrounding rocks and those governing deformation of supports are basically the same along the strike, but the displacements vary greatly. The front stresses affect greater areas than the lateral stresses and their limit widths of equilib-rium zones and K are almost similar. The stress transmits very deep. Our findings offer scientific basis on which to determine parameters for coal pillar retaining and for roadway out-laying, thus increasing the recovery ratio and improving the maintenance of roadway.

Study on gob-side entry retaining in fully-mechanized longwall with top-coal caving and its application

Based on the engineering background of gob-side entry retaining in fully-mechanized longwall with top coal caving(GER-FLTC) on N2105 working face of Yuwu coal mine, by adopting the methods of theoretical analysis and numerical calculation, the control techniques of surrounding rocks in GER-FLTC working face are studied in this paper. The two main difficulties of stability of surrounding rocks at gob-side retained entry in fully-mechanized longwall working face are the stability control of top coal and control of large deformation of GER-FLTC working face. Interaction mechanical model between roofing and roadside backfilling in GER-FLTC is established and the equations for the calculation of roof-cutting resistance of roadside backfilling are derived. Results of numerical calculation show that the damage zones of top coal can be categorized into the delaminating zone of top coal above the backfilling, tensile damage zone of top coal above the retained roadway and shear damage zone of the upper rib of the solid coal. Stability control of top coal is the critical part to success of GER-FLTC. With consideration of large deformation of surrounding rocks of gob-side retained entry in fully-mechanized longwall, the support technique of‘‘roofing control and wall strengthening'' is proposed where high strength and highly prestressed anchor rods and diagonal tensile anchor cables support are used for top coal, high strength and highly prestressed yielding anchor rod support is used for solid coal and roadside prestressed load-carrying backfilling is constructed by high-water material, in order to maintain the integrity of the top coal, transfer load, high resistance yielding load-carrying of solid coal, roof-cutting of roadside backfilling and support,and to achieve GER-FLTC. Results from this study are successfully applied in engineering practice.

SAFETY PROBLEMS IN FULLY-MECHANIZED TOP-COAL CAVING LONGWALL FACES

The thick-san top-ctal catrig technology has been in use in China for over a decade,and has given rise to siguscant economic efficiendes. Eftorts in reeent years to extend its applica tion to more complex mining conditions, mostly high-gas seams , with or without proneness ofspontaneous combustion. have brought about new safety problems This paper will highlight thefcatures and problems retared with thick-seam top-coal caving systems, compared with conventionai, fully-mecbanized longwall systems , particularly issues retated to methane, spontaneous combustion and dust,and disam the methods and measures to ded with them.

Study on safe thickness of overlying thin bedrock in fully-mechanized top-coal caving face with thick coal seam

To prevent support crush, the overlying strata safe thickness and its influential elements were studied by the adoption of theoretical analysis, numerical simulation and in-situ measurement. According to the production and geological condition of first face in Sima coal mine, the results indicate that the clay contains large permissible bearing ability and has better arching force. After mining destruction, stable structure is formed in bedrock to ensure face safety. The clay thickness ＆ bedrock thickness are the key influential elements to stable structure. The minimal bedrock thickness is about 40 m to ensure safe mining under loose surface soil condition. When surface soil contains mainly thick clay, it forms steady structure with the composition of thin bedrock, so that it can reduce minimal thickness of bedrock and to ensure safe mining. When clay thickness is 40 m, minimal bedrock thickness is 20 m. When clay thickness is 30 m, minimal bedrock thickness is 30 m. Bearing pressure peak ranges from 5 to 15 m in the front face under thin bedrock condition. The bearing pressure distribution range is 15 m. Main roof break distance is small, and initial weighting of main roof is not distinctive, while first periodic weighting of main roof is quite distinctive.

Analysis on distribution law of the abutment pressure of the integrated coal beside the road-in packing for gob-side entry retaining in fully-mechanized caving face

The three-dimensional damage constitutive relationship of coal is established and distribution law of the abutment pressure of the integrated coal beside the road-in packing for gob-side entry retaining in fully-mechanized caving face under the effect of given deformation of the main roof is analyzed by the damage mechanics theory. And the relationship between distribution of the abutment pressure and thickness of coal seam is explored. The presented result is of great theoretical significance and practical value to the study on stability control of the surrounding rock of road-in packing for gob-side entry retaining in fully-mechanized caving face.

Study on destressing technology for a roadway driven along goaf in a fully mechanized top-coal caving face

Based on the deformation characteristics of the roadways driven along goaf in fully mechanized top coal caving faces, the author considers that it is the key to ensure the stability of surrounding rocks of roadway driven along goaf to control the deformation during the period affected by mining. Considering the characteristics of the roadway layout in fully mechanized top coal caving faces, a technical scheme of destressing is put forward and the destressing effect is analyzed by using the software of Universal Distinct Element Code 3 0(UDEC 3 0).

Study of mechanical principle of floor heave of roadway driving along next goaf in fully mechanized sub-level caving face

Abstract On the basis of analyzing floor strata mechanical circumstance of the roadway, the mechanical model was established. The relative displacement of roadway floor, narrow pillar floor coal mass and floor strata was calculated, the results showed that the high abutment pressure on coal mass beside the roadway was the main reason to lead to relative displacement of floor strata. And the roadway floor heave come mainly from three aspects. Firstly, the roadway floor strata is easily fractured by the stretch stress. Secondly, because the high abutment pressure is greater than the uniaxial compressive strength of floor strata, when the roadway floor strata are fractured, the coal mass floor strata at the same depth will be fractured, and broken rock will fluid into the open roadway. Thirdly, comparing with the coal mass floor, the roadway floor is relative ascending.

Arrangement of anchor reinforcement in roadway for fully mechanized sublevel caving

Bolting of mining roadway for fully mechanized sublevel caving has been practised successfully in Hebi mining area.It provides a new method for roadway support and settles the problem of support difficulty radically for sublevel caving in Hebi mining area.Where anchor reinforcement holds an important station in roadway support.This article brings forward the arrangement project of anchor based on theoretic analysis.Compared with arranged in the middle of the entry, anchor arranged in the vertex of the entry can reduces the length of anchor,shortens the anchor installation time,and heightens the reliability of anchor installation.

近距离煤层采空区下综放工作面巷道合理位置研究

近距离煤层综放工作面开采空间大,采动强度高,下位煤层回采巷道受上煤层采动影响存在应力集中、巷道支护困难等问题,因此近距离煤层综放工作面巷道合理位置的选取对后期支护控制起到关键性作用。以西露天煤矿2煤层和1煤层1分层为研究对象,综合考虑了上煤层开采时的底板应力降低区域和下煤层开采时的极限平衡区域,确定了下煤层巷道的合理位置应在距离实体煤柱内错22.79 m以上的区域。基于上述理论计算结果,分析了上煤层开采后底板应力分布规律及不同内错距下巷道围岩变形破坏特征及规律,结果表明:①距离采空区底板越近,应力最大值与最小值相差越明显;②随着内错距不断增大,围岩应力和应力集中系数呈现急剧降低-缓慢增大-稳定的趋势,在内错距20~25 m内应力及应力集中系数相对较小;③巷道围岩塑性区范围呈现先减小后增大的趋势,当巷道处于内错20,25 m时巷道围岩破坏相对较小;④巷道变形量随着内错距增大而逐渐减小,当内错距增加至25 m时,巷道围岩移进量基本保持不变;⑤确定巷道合理内错距为20~25 m。工程应用结果表明:巷道采用内错距24 m布置时,巷道围岩松动破坏深度及变形量均在可控范围内,进一步证明了该内错距的合理性。

急倾斜中厚煤层单一巷道放顶煤采煤方法研究与应用

为解决某矿急倾斜中厚煤层倾角及厚度变化大的开采问题,提出了“急倾斜中厚煤层单一巷道放顶煤采煤方法”。该采煤方法是沿急倾斜煤层倾斜方向划分为若干区段,每个区段沿急倾斜煤层走向仅布置1条巷道。此巷道服务于1个采煤区段,担负工作面通风、运输和行人等任务。对单一巷道放顶煤采煤方法的巷道布置、综放工艺和沿空留巷方法进行了探讨。实践表明,该采煤方法使采煤工作面形成全负压通风,避免了巷道与采空区窜风,杜绝了采空区瓦斯积聚和遗煤自燃,实现了采煤机械化,提高了急倾斜中厚煤层的开采效率和煤炭回收率。单一巷道放顶煤采煤法为类似急倾斜煤层安全、高效开采提供了技术支撑。

孤岛综放工作面小煤柱沿空掘巷围岩控制技术研究

为提高同宝煤业15106孤岛工作面煤炭资源回收率,提出采用留小煤柱沿空掘巷技术施工辅运顺槽。通过理论计算和数值模拟分析确定了小煤柱宽度为8m,并提出了“锚网索+煤柱侧锚索梁加固+破碎区段煤柱侧巷帮注浆加固”的联合支护方案。应用结果表明:煤柱帮和实体煤帮最大位移量分别为223.56 mm、68.36mm,顶板最大下沉量为216.52mm,底鼓量最大值为172.54mm,沿空巷道围岩变形控制效果显著。此外,采用小煤柱沿空掘巷技术后,区段煤柱宽度由25m缩小至8m,可多回收煤柱资源约10.15万t,经济效益显著。

双临空综放面巷道变形能量时空演化机理及防治技术研究

以塔山矿8204-2特厚煤层综放不规则双临空工作面工程地质条件为背景,基于数值模拟揭示了不同煤柱宽度下采动应力及煤柱应变能密度分布特征。结果表明,双临空工作面回采期间,30~60 m宽的煤柱处于高应力状态,峰值超过25.96 MPa,为原岩应力的2.09倍;当煤柱宽度在30~60 m时,煤柱表现出高应力、高应变能密度的“两高”特点,发生强动压的危险性高。为防止三角变宽煤柱动力失稳,现场成功实践了“超深高密大直径卸压钻孔+补丁锚索加强支护”的强动压治理技术,使得巷道掘进和回采期间均未发生冲击地压及显著动压事故,实现了不规则综放面的安全回采。

综放工作面“以孔代巷”瓦斯治理技术应用

针对王家岭矿采煤工作面“厚煤层、高产量、瓦斯低含量”的特点,拟定采用顶板走向长钻孔代替高抽巷的瓦斯治理技术。以该矿18103工作面为工程实例,通过施工定向顶板走向长钻孔进行抽采试验,以验证“以孔代巷”瓦斯治理的可行性及有效性,应用取得显著效果。

综放面动压巷道失稳特征及控制技术研究

针对综放工作面动压巷道失稳问题,以河北某冲击地压矿井为工程背景,通过理论分析、数值模拟、实验室实验的方法对综放工作面动压巷道失稳特征进行了研究,结果表明:工作面采动应力多以动载荷形式作用于工作面煤体,煤体强度为18.3 MPa,煤体动力失稳与煤体储存弹性能、动载荷以及耗散能量有关,弹性能积聚与极限能量差越大,动力显现越明显,工作面超前段受到组合应力影响,弹性能储存相对较高,容易发生动力失稳,动载荷影响下,工作面动压巷道围岩塑性区逐渐增大并实现贯通,弹性区减小,容易诱发连锁动力失稳。针对不同诱发因素提出了顶板爆破、超前段钻孔卸压以及补强支护的方法,对顶板动载荷、超前采动应力以及巷道围岩破碎带进行处理。

综放开采回采巷道切顶护巷技术研究

厚煤层综放开采时由于一次开采厚度大,导致开采引起的采动压力影响范围、显现程度等均较为明显,给邻近巷道围岩控制工作带来一定影响。2301综放工作面运输巷与邻近的2303回风巷间留设25 m保护煤柱,受2301综放工作面开采影响导致2303回风巷变形量较大,难以满足后续使用需要。结合现场条件及以往研究成果,提出在2301运输巷靠近煤柱侧施工切顶钻孔,通过切顶较少2301综放工作面对2303回风巷影响,并对切顶布置方案、乳化炸药布置以及封孔方式等进行详细设计。现场应用后,2303回风巷围岩变形量受2301综放工作面开采影响较小,回风巷围岩变形量在允许范围内,可满足后续使用需要。

综放工作面小煤柱沿空掘巷煤柱尺寸留设研究

为合理留设综放工作面沿空掘巷煤柱,以山西某矿E4102-1工作面运输顺槽煤柱留设工程概况为例,通过进行调研分析与进行数值模拟分析,并结合工业性试验,得出窄煤柱沿空掘巷技术目前已相对较成熟,可把煤柱尺寸留设为5 m至8 m之间;通过对几种煤柱尺寸下的巷道围岩破坏状况进行数值模拟分析,得出该工作面巷道留设5 m宽的煤柱时,该巷道矿压不会出现明显显现,巷道变形量相对较小,巷道顶板也相对较稳定,能很好的满足矿井安全生产需求,更好地保障矿井安全生产。

综放工作面采空区侧巷道变形特征及控制研究

针对综放工作面采空区侧巷道严重的不对称变形破坏,以大同煤矿巷道为研究对象,通过数值模拟和现场试验,探讨了综放工作面采空区侧巷道变形特征及控制。研究结果表明,空区侧巷道围岩的不对称变形破坏与垮落厚度密切相关,主顶板应力位置随顶煤厚度的变化而变化。针对巷道的非对称变形特征,提出了以非对称高预应力桁架锚索支护为主的控制策略,在巷道修复段进行了现场试验。试验结果表明,巷道不对称变形得到了很好的控制,实现了巷道的长期稳定。

厚煤层综放工作面动压影响巷道围岩补强加固技术研究

以20102运输巷围岩控制工程为研究对象,对动压影响下巷道围岩变形特征进行了分析,发现运输巷围岩变形主要以顶板下沉、巷帮收敛为主。依据运输巷现场条件及围岩变形特征,制定了适合厚煤层动压影响巷道围岩的补强加固技术方案,并与原有支护体系相互配合,共同抵御强动压影响。工程应用后,在动压影响范围内20102运输巷顶底板、巷帮最大位移量分别为341、 492 mm,围岩变形量整体较小,可满足运输巷后续使用需求。