Mechanical mechanism of overlying strata breaking and development of fractured zone during close-distance coal seam group mining

This study mainly investigates the mechanical mechanism of overlying strata breaking and the development of fractured zones during close-distance coal seam group mining in the Gaojialiang coal mine.First,a mechanical model for the second"activation"of broken overlying strata is established,and the related mechanical"activation"conditions are obtained.A recursive formula for calculating the separation distance of overlying strata is deduced.Second,a height determining method for predicting the height of fractured zones during close-distance coal seam group mining is proposed based on two values,namely,the separation distance and ultimate subsidence value of overlying strata.This method is applied to calculate the fractured zone heights in nos.20107 and 20307 mining faces.The calculated results are almost equal to the field observation results.Third,a modified formula for calculating the height of a waterflowing fractured zone is proposed.A comparison of the calculated and observed results shows that the errors are small.The height determining method and modified formula not only build a theoretical foundation for water conservation mining at the Gaojialiang coal mine,but also provide a reference for estimating the height of water-flowing fractured zones in other coal mines with similar conditions.

Stress distribution rule of roadway affected by overhead mining in gently inclined coal seams group

In light of the severe deformation and destruction of the district raise tunnel in the mining area at the northern part of the Lubanshan colliery, by the theoretic analysis and numerical simulation, both the mining stress distribution in seams group and the deformation and destruction mechanism of floor district raise were investigated. The results show that, at the maximum vertical distance of 40 m, the abutment stress has an influence on the recovery of 2# and 3# coal seam and 8# coal seam at distance of 30 m. As a result, the recovery of 8# is rather than those of 2# or 3# coal seam, which contributes to the deformation and destruction of the district raise surrounding rock. The major factors affecting the abutment stress include the mining depth, mining height, residual gob space, adjacent working faces and short spacing coal seam recovery.

Numerical simulation and experimental research of surrounding rock deformation of floor roadway under short-distance coal seam group combined mining

According to the influence of the combination of short-distance coal seam group on mining roadway, using numerical simulation software FLAG2D to draw the abutment pressure distribution ahead the working face and the area of influence in fully-mechanized mining conditions, the variation rules of surrounding rock supporting pressure of floor roadway and the deformation rules were summarized. GYS-300 anchor dynamometer was used to measure the roadway surface displacement, and the conclusions of numerical simulation were verified.

Geological modeling of coalbed methane reservoirs in the tectonically deformed coal seam group in the Dahebian block,western Guizhou,China

The widely spread Carboniferous-Permian coal seam group in southern China has great potential for coalbed methane resources,but the extensively developed tectonically deformed coal seriously restricts its development.Taking the Dahebian block in western Guizhou as the study area,the geological model of coalbed methane reservoirs in the tectonically deformed coal seam group was established,and the spatial distribution pattern of model parameters was clarified by clustering algorithms and factor analysis.The facies model suggests that the main coal body structures in Nos.1,4,and 7 coal seams are cataclastic coal and granulated coal,whereas the No.11 coal seam is dominated by granulated coal,which has larger thicknesses and spreads more continuously.The in situ permeability of primary undeformed coal,cataclastic coal,granulated coal,and mylonitized coal reservoirs are 0.333 mD,0.931 mD,0.146 mD,and 0.099 mD,respectively,according to the production performance analysis method.The property model constructed by facies-controlled modeling reveals that Nos.1,4,and 7 coal seams have a wider high-permeability area,but the gas content is lower;the high-permeability area in the No.11 coal seam is more limited,but the gas content is higher.The results of the self-organizing map neural network and K-means clustering indicate that the geological model can be divided into 6 clusters,the model parameter characteristics of the 6 clusters are summarized by data analysis in combination with 6 factors extracted by factor analysis,and the application of data analysis results in multi-layer coalbed methane co-development is presented.This study provides ideas for the geological modeling in the tectonically deformed coal seam group and its data analysis.

Reasonable location of stopping line in close‑distance underlying coal seam and partition support of large cross‑section roadway

Close-distance coal seams are widely distributed over China,and the coal pillars left by the overlying coal seams afect the retracement channel of the underlying coal seam in the stopping stage.Based on the engineering background of close-distance seam mining in a coal mine,the reasonable position of the underlying coal seam's stopping line and the support method of the large section roadway during stopping are investigated using feld measurements,similar simulation experiments,and numerical simulations.There are three types of location relationships between the stopping line of the underlying coal seam and the stopping line of the overlying coal seam:"externally staggered with the upper stopping line"(ESUL,stops mining under the overlying goaf),"overlapped with upper stopping line"(OUL),and"internally staggered with the upper stopping line"(ISUL,ISUL-SD for shorter internal staggered distances,ISUL-LD for longer ones).There are diferent stress arch structures in the overlying strata of the above three positions,and the stress arch evolution process exists in the process of ESUL→OUL→ISUL-SD→ISUL-LD:a front and rear double stress arch structure→the front arch gradually decreases→the front arch dies out,and the double arch synthesizes the single arch→the single-arch range expands→the nested double arch.The relationship between the stress arch structure and the position of the stopping line is evaluated as follows:(1)ESUL:the stress concentration in the roof plate of the retracement channel of the underlying coal seam is the highest,because the overburden block of the extensive collapse zone acts directly on the roof plate of the retracement channel,resulting in relative difculties in roof support.(2)OUL:although the retracement channel roof pressure is minimal,the overlying rock structure has the potential for rotation or slippage instability.(3)ISUL-SD:the pressure on the roof of the retracement channel is small and the overburden structure is stable,which is conducive to the safe retraction of the support and not limited by the width of the end-mining coal pillar.(4)ISUL-LD:it is basically the same as the condition of stopping under the non-goaf;however,it has a limitation on the width of the end-mining coal pillar.The location of the stopping line is selected as ISUL-SD,and the retraction process of the self-excavating retraction channel was adopted.A partition asymmetric support scheme which is proven by feld practice is proposed,through a comprehensive analysis of the pre-stress feld simulation of the support scheme,based on the diferent control requirements of the roof above the support and the roof of the retracement channel in the stopping area.This method realizes safe and smooth withdrawal of the support.

Technical scheme and application of pressure-relief gas extraction in multi-coal seam mining region

A pressure relief gas extraction technical model of a typical mining area is proposed based on coal and gas simultaneous extraction theory. Flac3 Dwas employed to model vertical stress and displacement contour plot characteristics of non-outburst coal seam(No. 4) on top of outburst coal seam(No. 2) along strike and incline directions. Field investigations were also conducted to verify the scientific nature of the simulation. The results demonstrate that gas pressure in No. 2 coal seam dropped to approximately 0.55 MPa in the pressure relief multi-coal seam. The highest expansion rate of the coal mine reached up to 2.58%.The pressure-relief angle was 76° along the incline direction and 60° along the strike direction. As the expansion rate and pressure-relief angle increased and the gas pressure decreased, a large amount of gas flowed into the gob of No. 4 from No. 2 coal seam and was later discharged through specific gas pipes,which eliminated No. 2 outburst risks. This study resulted in positive outcomes in that gas extraction time was reduced by 13.5 days, due to pressure relief, and drilling work load was reduced by 0.1161 m/t coal. This method ensures that gas is discharged from the outburst coal seam quickly and safely,demonstrating that the proposed technical model of pressure-relief gas extraction is effective in a multi-coal seam region.

倾斜煤层群覆岩“三场”非对称特征及靶向抽采机制

倾斜煤层群“三场”(应力场、位移场和裂隙场)演化规律较为复杂,对卸压瓦斯运移和储集具有重要意义。为了探究倾斜煤层群“三场”演化规律,研究以新疆1930煤矿为对象,开展了倾斜煤层群多重采动相似模拟实验。分析了上覆岩层垮落形态,获得了覆岩应力演化特征,分析了覆岩位移分布和移动方向特征,阐明了采动裂隙分布特征。进而探究了三场演化规律对瓦斯运移的影响,并开展了定向钻孔瓦斯抽采现场试验进行验证。研究结果表明:倾斜煤层群多重采动下,采动裂隙矩形梯台呈现明显的非对称特征。低位侧覆岩应力变化较大,随开采次数增加,卸压效应更为明显,而高位侧覆岩应力变化较小;结合重力−倾角效应,高位侧覆岩更易破坏,垮落次序优先,呈非对称特征。覆岩位移分布呈非对称特征,高位侧位移显著且移动方向变化较大。高位侧裂隙区网格内采动裂隙频数明显高于低位侧;高位侧裂隙区破断裂隙分布更多,且开度较大;采动裂隙呈“高位扩展−低位压缩”的非对称特征。多重采动使得“三场”非对称特征更为显著。此外,覆岩贯通度存在“慢速减小−快速减小”的现象。基于“三场”演化特征和瓦斯运移的关系,揭示了瓦斯抽采靶向优选机制。结合试验结果,构建了基于“三场”演化规律的裂隙带瓦斯抽采靶点区判定流程。现场瓦斯抽采效果良好,保证了工作面安全高效回采。研究结果为倾斜煤层群卸压瓦斯精准抽采提供了理论参考,旨在提高倾斜煤层群瓦斯抽采量,防止上隅角瓦斯超限,实现倾斜煤层群安全高效开采。

深部近距离煤层群下分层巷道分区支护技术

为实现深部近距离煤层群下分层巷道安全,以张双楼煤矿21916工作面为工程背景,分析了工作面冲击地压影响因素,划分了21916工作面掘进期间巷道冲击危险区域;建立了煤层合并区域下分层回采巷道数值模型,研究了9煤层21916工作面巷道内错7煤采空区不同距离时应力和位移分布规律,确定了下分层巷道合理位置;基于冲击危险区域划分结果,提出了分区支护技术,并设计了支护参数。现场实测表明,下分层巷道最大两帮移近量为164 mm,最大顶底板移近量为84 mm,顶板深部和浅部的离层量不大于3 mm,帮部锚杆和顶部的锚索受力变化较小,顶锚杆受力从8 kN增加到12 kN后趋于稳定,表明21916工作面巷道布置合理,分区防冲支护技术合理,支护质量与效果显著。研究结果可为类似条件工作面防冲支护提供借鉴。

煤层群采动下围岩应力演化规律及协同控制技术研究

针对煤层群开采过程中巷道支护困难问题,以贵州土城矿212回风石门为工程背景。综合采用现场调研、数值模拟、相似模拟及现场试验等手段,揭示了212回风石门应力演化规律,并提出了“卸−转−固”协同控制技术。研究结果表明:212回风石门遭受破坏的主要原因是煤层群采动过程中存在的地质力学问题导致了围岩失稳。巷道底板及两帮在采动过程中产生不同程度的应力集中。当遭受垂直应力挤压时,巷道底部承受的挤压力较大,而顶部围岩承受的拉伸力较大,由于力学不平衡导致围岩的破坏。基于此提出了“卸−转−固”协同控制技术。通过爆破卸压的方式,利用爆破产生的冲击波引起围岩的震动和应力波动,使表层围岩中原本集中的应力分散到更深的围岩区域,降低表层围岩的应力集中程度。同时,利用爆轰和封孔工艺进一步加固卸压孔周围的围岩,形成两个承载结构。即由巷道支护体形成的内承载体和由深部围岩形成的外承载体。两者相互作用有效承受巷道浅部及深部围岩的应力,并转移到支护结构,起到保护和稳定围岩的作用。利用该技术在212回风石门现场试验,结果显示:使用该技术区域应力长期趋于稳定甚至缓慢降低,巷道顶底板及两帮移近速率分别降低了74.49%及47.67%,底鼓量降低了77.2%。而未使用该技术区域应力出现不同程度的上升,表面位移收敛严重。由此可得,围岩控制效果显著。该技术已成功推广到贵州其他不同地质环境的煤矿,均取得了显著效果。

远距离斜交工作面上行开采上组煤垂直应力演化规律

为探究平煤八矿远距离煤层群斜交工作面上行开采过程中上组煤层垂直应力演化规律,采用数值模拟计算的方法展开研究。研究结果表明,己_(15)-21030工作面回采过程中与上覆戊_(9.10)-21070工作面依次形成相离、相交和重叠的空间关系,因此会使上组煤层应力增高或降低。相离区域为应力升高区,受下组煤采动影响应力整体呈升高趋势,应力集中系数最大为1.18;相交区域为卸压过渡区,戊_(9.10)-21070工作面应力由增压变为卸压,最大卸压值较原始应力降低了25%,倾向卸压影响范围为55 m;重叠区域为卸压区,受己_(15)-21030工作面采动影响卸压效果及卸压范围均进一步增大,最大卸压值较原始应力降低了40%,倾向卸压影响范围增大至180 m。将戊组煤层戊_(9.10)-21070工作面根据应力分布云图依次划分为增压区、应力过渡区、卸压区和稳定卸压区。通过现场瓦斯含量测试验证了卸压区残余瓦斯含量比原始区域残余瓦斯含量降低32.9%,远距离煤层群上行开采形成卸压区有利于瓦斯治理工作的开展。

神东矿区浅埋煤层开采地表裂隙分布及动态演化特征研究

神东矿区浅埋煤层群开采导致地表裂隙发育良好,立体漏风复杂。为研究神东矿区地表裂隙分布特征及动态演化规律,以大柳塔煤矿活鸡兔井和补连塔煤矿浅埋藏开采为工程背景,采用现场无人机定点观测、红外、地质雷达等技术相结合的方法,研究地表宏观裂隙、隐蔽裂隙分布特征,并对裂隙动态演化规律进行分析。结果表明:神东矿区浅埋煤层开采工作面采空区对地表走向裂隙的影响相比于倾向裂隙较大,其中活鸡兔井12下206工作面101条裂隙有效影响范围35 m,补连塔煤矿22310工作面122条裂隙为62 m,走向裂隙最大裂隙宽度达到80 cm,倾向裂隙普遍在10 cm以下;随工作面的推进,裂隙宽度逐渐变大,直至发育完全,裂缝位置不连续断面间距变大,落差增大;宽度较大的裂隙(裂隙宽度大于10 cm),如果距离工作面较近,随着工作面的推进,裂隙宽度会逐渐缩小,甚至可能闭合。

煤层群叠加开采覆岩裂隙演化及卸压瓦斯抽采研究

针对采动裂隙带卸压瓦斯抽采效果不佳导致的工作面上隅角瓦斯超限的问题。以赵家寨煤矿11210工作面为工程背景,采用物理相似模拟实验方法,研究了煤层群叠加开采对上覆岩层采动裂隙的演化特征,并通过现场验证确定了瓦斯抽采的最优层位。结果表明:煤层群叠加开采过程中,在卸压区域外,形成了较大的应力集中,在卸压保护范围内,应力集中现象不明显,且应力峰值小于二1煤层原始应力;煤层群叠加开采引起了采场上覆岩层的叠加卸压,使上覆岩层的位移场发生了叠加变化,岩层最大下沉量进一步增加;煤层群叠加开采结束后,采空区上覆岩层中部岩层被压实,两端岩层裂隙较为发育,形成了一定范围的裂隙发育区。通过现场试验,确定了裂隙带定向长钻孔合理层位的选择,并在现场进行钻孔监测,验证了物理相似模拟结果的合理性。

表面活性剂对无烟煤润湿性的影响实验研究

煤的润湿性对煤层注水及防尘有重要意义。为研究表面活性剂对煤尘表面润湿性的影响机理,以贵州矿区无烟煤为研究对象开展煤尘沉降实验,优选润湿实验煤样效果最佳的表面活性剂溶液,借助红外光谱实验及Zeta电位测定实验,探索表面活性剂作用下煤表面润湿性的变化规律。研究结果表明:实验所用4种表面活性剂均能大幅度提高煤尘润湿性;其中,质量分数为1%的APG润湿煤尘的效果最佳;改性后,实验煤样亲水基团和疏水基团均增加,但亲水基团增量明显大于疏水基团,说明表面活性剂改性对亲水基团的影响更显著,有利于提高煤尘表面的亲水性;改性后,实验煤样表面负电性增强约7.68倍,引起双电层中剪切面滑向液面,同时强化含氧官能团与水分子之间的偶极作用力,导致水化层增厚,煤样表面润湿性得以改善。

覆岩应力-漏风综合影响下浅埋煤层群下煤层开采巷道布置研究

针对浅埋近距离煤层群上部遗留煤柱影响下的下部工作面巷道合理布置位置确定问题,以活鸡兔井为例,采用离散元方法(DEM)模拟研究了遗留煤柱底板应力分布与上、下煤层开采采空区裂隙发育特征。结果表明:12号煤层开采过后,22号煤层水平距上覆煤柱20 m内为垂向应力与主应力差增高区,22号煤层水平应力在区段煤柱内侧较低;下煤层巷道布置采用外错式与重叠式时,巷道两侧围岩主应力差较大,且外错式与重叠式布置方式下22号煤层工作面开采时夹层与上部老空区覆岩二次运移剧烈,采空区两侧斜向裂缝带发育与贯通较好;采用内错式,巷道两侧围岩主应力差随与煤柱距离增大先降低、后升高,在距煤柱25~35 m处主应力差达到最低,且该布置方式下上部采空区覆岩沉降均衡,裂缝带闭合性较好,极大阻止了地表与层间贯通漏风通道的发育。

煤层群中断层对采动裂隙演化规律的影响研究

为研究断层对煤层群采动裂隙演化规律的影响,以贵州土城煤矿151710工作面为研究对象,基于相似模拟和数值模拟方法对含断层煤层群采动裂隙演化规律进行研究。结果表明:含断层煤层群中9号、12号煤层开采到相同距离时工作面周围应力分布显著不同;9号煤层的超前开采,使12号煤层处于应力降低区,过断层开采时工作面前后出现应力分区现象;随着开采的进行,12号煤层的采动影响范围小于9号煤层;当开采工作面过断层时,覆岩裂隙发育迅速,岩层间出现显著离层,并发生不同程度的断裂。现场12号煤层回风巷顶板钻孔窥视显示:当工作面过断层时,顶板破碎严重,覆岩裂隙发育杂乱。

缓倾斜煤层群开采辅助运输系统改造及开拓优化设计

针对缓倾斜煤层群开发过程中由于辅助提升及运输系统复杂引起的一系列问题,提出以无轨化辅助运输系统为改造目标,以新建缓坡斜井为改造方式,对沙吉海一号矿井进行辅助提升及运输系统改造。结合井筒布置情况,对矿井进行开拓优化设计,采用缓坡斜井兼做采区辅助运输上山的方式开发煤层群,减少采区个数,延长各采区服务年限,有利于缓解矿井采掘接续紧张的局面。对于新疆地区煤层群开发,沙吉海一号矿井开拓优化思路有一定的借鉴意义。

浅埋近煤层群采动“三区”漏风裂隙场时空演化规律数值模拟

浅埋近煤层群采动下,地面采空区工作面“三区”之间易形成连通的漏气通道引发工作面低氧和采空区煤自燃,如何厘清采动效应下浅埋煤层群“三区”漏气通道的时空分布演化规律是有效防控煤自燃和低氧的关键。以陕煤柠条塔煤矿S1232工作面为研究背景,采用理论与数值模拟相结合的方法,研究了单一煤层、复合煤层重复开采下覆岩破坏特征,分析了煤层间距与采厚对裂隙二次发育的影响规律。结果表明:浅埋近煤层群开采下上覆岩层裂隙仅存在垮落带与裂缝带,主关键层破断后裂缝带快速发育至地表,关键层周期破断控制地表裂隙周期生成与下沉;上煤层裂隙密度发育由原始阶段先后经历快速增长、稳定和二次增长3个阶段;随采厚增大,各区间裂隙密度增大,大裂隙发育更充分,裂隙宽度整体增大;随煤层间距增大,小于0.2 m的裂隙宽度随采厚增大,且增加的速度逐渐加快,大于0.2 m的裂隙宽度随采厚增大,但增加速度逐渐变缓;采厚相同时,裂隙宽度大于0.2 m的裂隙密度随着煤层间距的增大逐渐减小。

低透气性突出煤层群首采层水力割缝卸压抽采技术研究

针对中近距离松软低透气性突出煤层群抽采防突难题,以皖北矿区任楼煤矿突出煤层群瓦斯地质条件为工程背景,在对松软煤层水力割缝卸压增透机制、首采层割缝工艺参数等研究的基础上,提出了首采层煤巷条带水力割缝卸压增透、煤层群瓦斯联合抽采的综合治理技术,优化了钻孔布置方式,并进行了工程应用。结果表明:割缝实施后钻孔的瓦斯抽采浓度、单孔日均抽采纯量分别是常规钻孔的4.27倍、3.94倍,煤层透气性提高了22~31倍,首采层72号煤层割缝后的防突有效半径可提高至5 m以上,检验抽采半径5 m处的瓦斯含量指标为4.13 m 3/t,在有效解决首采层煤巷条带瓦斯灾害的同时,钻孔工程量降低了2/3以上。

低变质程度煤层自然发火标志气体预警值和临界值确定

低变质程度煤层中具有较多活性基团,活性基团使煤层具有低温氧化特性,煤矿生产过程中,低变质程度煤层采煤工作面回风隅角CO体积浓度较高。为确定低变质程度煤层自然发火标志气体预警值和临界值,建立了采空区内部温度分布和回风隅角CO体积浓度预测数学模型,以122109工作面为例,利用该模型进行了测试。结果表明:回风隅角自然发火标志气体CO的预警值和临界值分别为94.4×10^(-6)、346.2×10^(-6),根据测试结果建立了煤层自然发火分级预警指标。通过案例测试表明,以采空区内部温度分布为基础的回风隅角CO体积浓度预测模型能很好地应用于低变质程度煤层。

近距离薄煤层群首采层卸压瓦斯协同抽采技术研究

为有效解决近距离薄煤层群开采首采层上、下邻近层大量卸压瓦斯涌入的治理问题,以某煤矿为研究对象,采用理论分析和数值模拟的方法,研究近距离薄煤层群开采条件下卸压瓦斯运移规律,并根据富集特征确定卸压瓦斯抽采钻孔的空间位置。研究结果表明:首采层开采覆岩导气裂隙带最大发育高为10.3~23.2 m。设计超大直径顺层预抽钻孔高0.8 m,宽2.08 m;顶板定向长钻孔终孔最优抽采位置为垂直距离开采层顶板15.0~23.0 m,水平距离回风侧20.5~27.5 m;2条埋管抽采最佳错距为距底板高1.1,1.7 m,深入采空区11.3,20.8 m。优化后的布置参数应用于现场实践,试验工作面回采期间上隅角瓦斯体积分数保持在0.7%以下。研究结果能够实现近距离薄煤层群开采条件下卸压瓦斯高效抽采,保证矿井安全高效生产。