A new method determining safe thickness of karst cave roof under pile tip

Cave roofs are used to support pile foundation in many engineering projects. Accurate stability analysis method of cave roof under pile tip is important in order to ensure the safety of the pile foundation structure. Firstly the mechanical model to analysis the stability of cave roof under pile tip is founded aiming to solve the problems that the simplified mechanical model has. Secondly, the boundary of cave roof is simply supposed to be supported according to the integrity of the rock mass in the boundary of cave roof. Thirdly, based on the theory of plates and shells, the simplified model is calculated and the theoretical calculation formula to determine the safe thickness of cave roof under pile tip can be obtained when the edges of the cave roof are simply supported. In the end, the analysis of the practical engineering project proves the feasibility and the rationality of the method which can be a new method to calculate the safe thickness of cave roof under pile tip.

Stability analysis of subgrade cave roofs in karst region

According to the engineering features of subgrade cave roof in karst region, the clamped beam model of subgrade cave roof in karst region was set up. Based on the catastrophe theory, the cusp catastrophe model for bearing capacity of subgrade cave roof and safe thickness of subgrade cave roof in karst region was established. The necessary instability conditions of subgrade cave roof were deduced, and then the methods to determine safe thickness of cave roofs under piles and bearing capacity of subgrade cave roof were proposed. At the same time, a practical engineering project was applied to verifying this method, which has been proved successfu1ly. At last, the major factors that affect the stability on cave roof under pile in karst region were deeply discussed and some results in quality were acquired.

Failure of hanging roofs in sublevel caving by shock collision and stress superposition

Hanging roofs or high hang-ups.a common problem in sublevel caving mining,usually result in a large ore loss and undermine mining safety.This paper analyzed the formation of a hanging roof and showed that increased confining pressure and reduced free surface were its main characteristics.In order to break down a hanging roof,a new method based on shock wave collision and stress superposition was developed.In this method,two blastholes containing multi-primer at different positions are simultaneously initiated at first.By doing this,a new free surface and a swell room can be created.After these holes are fired,a long delay time is given to the next blasthole so that the fragments from the first twohole blasting have enough time to fall down.This new method was applied to three hanging roofs in one production area,and all of them were successfully broken down.Field inspection indicated that almost no damage was caused in the nearby drifts/tunnels due to the new method.In addition,the far field vibrations were found to be smaller than the maximum vibrations induced by some other blasts.

Numerical analysis of application for induction caving roof

New method for handling roof of the base successive mining is proposed, which is induction caving in the roof. The key is that it is made certain to the station of the space-time in the induction caving roof, as the stress is released with the mining process. And applying the catastrophe theory, the influencing factors of induction caving roof are studied in the emptied areas, such as the mechanical property of the surrounding rock, the area of the gob,the scope and dimension of tensile stress. The results show that the key factor is the area of the gob to the method of the induction caving roof. Then according to the geology and the ore characteristic, the three dimension FEM mechanical model is built in Tongkeng Mine, the laws of the tensile stress are analyzed to the space and the time in the roof with the mining, then it is rational design to the mine step and time of the handing the roof.

Similar material simulation of time series system for induced caving of roof in continuous mining under backfill

With the help of similar material simulation test,time series system for induced caving of roof in continuous mining under complex backfill in ore body No.92 of Tongkeng Tin Mine was studied. According to the similarity theory,a two-dimensional similar simulation test-bed was constructed. The stress and displacement that change along with the advance of mining were acquired and analyzed automatically by data system. The processes of continuous mining of ore-block in 5 intervals and artificial induced caving of roof were simulated. The results of the test show that ore body remained as safety roof in thickness of 15 m guarantees the safe advance of stoping work face. Caving of safety roof puts in practice at the first two mining intervals when the third interval of continuous mining is finished,and one interval as the safety distance should be kept all the time between stopping and caving. While mining in the last interval,pre-slotting should be implemented first of all,and the roof of the last two mining intervals is caved simultaneously. Only this kind of time series system can be an efficient and safe way for induced caving of roof in continuous mining.

Numerical simulation of roof cavings in several Kuzbass mines using finite-difference continuum damage mechanics approach

An essential stage of mine design is an estimation of the steps of the first and periodic roof caving in longwall mines.Generally,this is carried out using the field experience and can be much enhanced by numerical simulation.In this work,the finite-difference method was applied coupled with the continuum damage mechanics(CDM)approach to simulate the stress-strain evolution of the rock mass with the underground opening during coal extraction.The steps and stages of roof caving were estimated relying on the numerical simulation data,and they were compared with the field data from several operating mines in the south of the Kuznetsk Basin,Russia.The dependence of the first roof caving step in simulation linearly correlates with field data.The results correspond to the actual roofs of longwall panels of the flat-dipping coal seams and the average rate of face advancement is approximately 5 m/day.

Similar material simulation research on movement law of roof over-lying strata in stope of fully mechanized caving face with large mining height

Similar material simulation test W9-15 101 fully mechanized caving face with was carried out in a geological model of large mining height in the Liuhuanggou Colliery, in Xinjiang Uigur Autonomous Region. The roof overlying strata movement law in the stope of a fully mechanized caving face with large mining height was studied and show that the roof overlying strata in the stope of a fully mechanized caving face with large mining height can be formed into a stable arch structure; the fracture rock beam is formed resembling a ＂bond beam＂, but it has essentially the structure of ＂multi-span beams＂ under the big structure of the stable arch. The roof overlying strata movement law in the stope of a fully mechanized caving face with large mining height is similar to that of the common, fully mechanized caving stope, which is determined by the deformation and instability of the structure of ＂multi-span beams＂. But because of the differences between the mining heights, the peak pressure in the stope of a fully mechanized caving face with large mining height is smaller while the affected area of abutment pressure is wider in the front of the working face; this is the obvious difference in abutment pressure between the stope of a fully mechanized caving face with large mining height and that of the common.

Relationship between water inrush from coal seam floors and main roof weighting

A water-resistant key strata model of a goaf floor prior to main roof weighting was developed to explore the relationship between water inrush from the floor and main roof weighting. The stress distribution,broken characteristics, and the risk area for water inrush of the water-resistant key strata were analysed using elastic thin plate theory. The formula of the maximum water pressure tolerated by the waterresistant key strata was deduced. The effects of the caved load of the goaf, the goaf size prior to main roof weighting, the advancing distance of the workface or weighting step, and the thickness of the waterresistant key strata on the breaking and instability of the water-resistant key strata were analysed.The results indicate that the water inrush from the floor can be predicted and prevented by controlling the initial or periodic weighting step with measures such as artificial forced caving, thus achieving safe mining conditions above confined aquifers. The findings provide an important theoretical basis for determining water inrush from the floor when mining above confined aquifers.

Breaking mechanism and control technology of sandstone straight roof in thin bedrock stope

The key problem to be solved urgently is how to avoid the occurrence of support break-off and water inrush in the stoping of sandstone straight roof under the action of load transfer in unconsolidated aquifer.For this reason,taking the thin bedrock 1602(3)working face of Huainan(the middle part of Anhui Province)Panyi Coal Mine as the engineering background,this study establishes the stope mining model by using the discrete element UDEC software and the mathematics mechanical model of the support load,and analyzes the reason of support crushing and decides to re-mining the working face by using the compulsive roof caving method.It is concluded that when the working face of sandstone straight roof is broken,the"voussoir beam"structure cannot be formed and acts on the support in the form of cantilever beam,but only when it falls to the high key stratum can the"voussoir beam"structure be formed and at this point,at this time,the bracket bears the weight of the rock layer in the range from the fractured sandstone layer to the lower critical layer.The working resistance of the support increases with the increase of the thickness and the breaking length of straight sandstone roof.When the breaking length of the roof reaches a certain extreme value,the support crushing accidents will occur.Managing roof with compulsive roof caving method can reduce the intensity of rock pressure in the stope,and the working face can be safely stoped,which provides a certain reference for similar conditions.

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.

北石窟寺平顶窟顶板层状剥落破坏力学机制研究

以庆阳北石窟寺为代表的陇东石窟多开凿于弱胶结砂岩地层,呈现结构松散、胶结物含量与强度低、沉积原生层理面黏结力弱等特点,平顶窟容易发育顶板层状剥落病害。选取北石窟寺10处具有典型剥落病害特征的洞窟进行调查,获取岩层剥落病害的几何参数及分布特征。调查发现北石窟寺平顶窟顶板层状剥落的破坏特征呈现多阶段性,从底部最大拉应力区域开始发育裂缝,逐渐向上扩展剥落,形成步进式坍塌,直至构成稳定的极限平衡拱。考虑上覆荷载、层理面黏接力、端部支撑和水平构造应力等多种因素的综合作用,逐步推导了从固支梁模型到简支梁模型、悬臂梁模型,最终形成极限平衡拱模型的渐近演化过程,并结合结构力学和弹性力学理论建立了不同损伤阶段的典型力学模型,揭示了顶板层状剥落不同阶段病害特征和破坏机制,并提出了不同阶段破坏的临界范围及阈值。研究成果能够更精确预测砂岩平顶窟失稳趋势,可为顶板岩体稳定性评价和预防性保护提供理论支撑,对同类石窟的长期保护具有重要参考价值。

桥梁荷载作用下巨型岩溶洞穴顶板稳定性研究

某高速公路桥墩基础完全置于巨型溶腔上部,通过定性、半定量、定量的方法对岩溶洞穴顶板稳定性进行综合分析评价,确定了桥型方案,然后通过地表变形监测,验证稳定性综合评价方法的合理性。

两次采动影响下小煤柱巷道切顶卸压围岩控制技术

为解决多次采动影响下留小煤柱巷道矿压显现剧烈、围岩变形量大的问题,提出了“切顶卸压+顶、帮锚索补强”联合控制技术。以贾家沟煤矿10115运输巷为工程背景,分析了切顶卸压位置、高度与巷道围岩垂直应力分布的关系,给出切顶卸压关键参数,并研究了留小煤柱巷道在切顶卸压后受两次采动影响下的矿压显现规律。结果表明:切顶卸压后,煤柱上的应力峰值随切顶深度的增加呈指数降低;10115运输巷在邻近工作面一次采动过程中巷道围岩变形依次呈现出无变形、缓慢变形、快速变形和围岩稳定的变化规律,本工作面二次采动过程中巷道围岩变形依次呈现出明显变形和剧烈变形的规律;巷道围岩在受二次采动影响时变形更加剧烈,巷道变形量为一次采动时的3.0~7.5倍。

倾斜矿体多采空区顶板破坏与冒落机理分析

排山楼金矿上部矿体露天转地下阶段应用空场法开采,采空区已用诱导冒落+地表废石充填塌陷区的方法进行了治理;下部矿体进入海棠山国家自然保护区范围,地表不允许塌陷,但由于矿石品位低,继续沿用传统充填法势必造成矿床开采效率低、生产成本高、矿山经济效益差等问题。以地表保护区下低品位矿体充填法安全高效开采为工程背景,结合RG井下电视系统监测结果总结了顶板上覆岩层裂隙分布与发展规律,分析了应力平衡拱与冒落拱演化机理,提出了稳定冒落拱的形成条件。基于现场监测与岩石力学参数试验结果,通过FLAC^(3D)数值模拟方法研究了倾斜多空区贯通与拉底过程中顶板破坏与冒落机理,探明了顶板冒落过程中围岩的应力和位移演化规律,以及诱发冒落的主导因素,并提出了基于地表安全性的冒落进程控制技术。研究成果可为该矿开发既满足地表保护需求又能低成本高效开采的工艺技术提供理论参考,对于类似矿山的采矿方法设计也有一定的借鉴意义。

高瓦斯综放面开切眼架前膨胀预裂坚硬顶板切顶技术研究

针对高瓦斯坚硬顶板综放工作面初采期来压步距大及顶煤损失的问题,提出代替火药爆破的开切眼架前及两顺槽煤柱侧静态膨胀预裂切顶技术;采用数值模拟方法确定了静态膨胀预裂切顶的关键参数,设计了切顶方案及工艺,并通过现场工程应用验证了静态膨胀预裂切顶技术的有效性。结果表明:综放工作面初采前在开切眼架前及两顺槽煤柱侧实施静态膨胀预裂切顶,既保证了开切眼设备安装期间的安全性,又可在后续采动应力的作用下顶板及时破断,减小坚硬顶板初次来压步距和强度;当综放工作面初采推进至开切眼宽度时发生初次来压,人工减跨效果良好,不仅提前回收了工作面的顶煤资源,而且还消除了坚硬顶板大面积悬顶带来的诸多重大安全隐患,研究成果可在类似条件下代替炸药爆破进行推广应用。

综采工作面顶板定向水力压裂技术应用

为解决主采煤层存在巨厚坚硬顶板,造成初次来压期间矿压显现严重,工作面局部支架压死的难题,对3104工作面地质条件进行分析,对目标层位实施定向水力压裂措施,并对初次来压期间工作面矿压显现、支架工作阻力变化情况进行观测、分析和对比,确定其初次来压步距。观测结果表明:在开展顶板定向水力压裂措施后,3104工作面基本顶初次来压步距30.8 m,相比原始状态顶板,减少54.9%。实践证明:对于上覆厚层坚硬顶板,通过定向水力压裂措施对顶板进行压裂是有效可行的工作面初次放顶技术。

厚硬顶板刀把形采空区下综放工作面冲击地压机制研究

不规则的开采空间结构可增大煤矿冲击地压危险,研究多煤层复杂开采空间结构下工作面冲击机制对煤炭资源安全采出具有重要意义。综合采用理论分析、数值模拟、现场监测等方法,研究了某矿井W1123综放工作面的动静载分布特征,分析了冲击显现机制,提出了针对性的防冲措施并进行现场应用。结果表明,上覆刀把形采空区和厚硬顶板综合作用下W1123工作面动静载分布具有区域性特征,当工作面仅受到刀把形采空区的“刀柄”作用或同时受“刀柄”和“刀身”作用时,工作面中下部和区段煤柱静载集中、动载扰动剧烈,工作面回风巷围岩也存在动静载集中,且距离刀把形采空边界越近则围岩动静载越高;仅受“刀身”作用时,工作面回风巷围岩静载集中受动载扰动。工作面静载集中区和动载扰动区重合,动静载叠加造成冲击显现。依据刀把形采空区结构特征,W1123工作面回采期间冲击类型依次为强动载型、高静载强动载型、高静载型。数值模拟和现场监测揭示的冲击危险区与理论分析结果一致。针对W1123工作面静动载分布特征,优化设计了冲击地压防治措施,增大了厚硬顶板处理高度和破碎程度、增加了工作面运输巷煤体爆破和煤柱切顶以降低顶板和煤体应力和能量集中;优化措施实施后,工作面微震事件日均能量总体下降54%,大能量事件大幅减少,冲击地压危险显著降低。该研究结果可为相似条件矿井的冲击地压防治提供借鉴。

综采工作面坚硬顶板深孔预裂爆破技术应用研究

井工煤矿进行煤炭开采时,采煤工作面的矿压显现主要受工作面上方顶板的影响,特别是坚硬顶板,影响更大。坚硬顶板造成的综采工作面采空区顶板悬顶面积过大对综采工作面的矿压显现及安全生产有很大影响。回采过程中,坚硬顶板不能随着工作面向前推进及时垮落,会形成大面积悬顶,如果大面积顶板突然垮落,不仅会砸毁设备,破坏工作面,还会产生强烈的冲击波,造成人员伤亡,形成矿难。为了防治井下采煤时坚硬顶板突然垮落造成的安全隐患,塬林煤矿根据W1-108工作面实际情况,决定采用深孔预裂爆破强制放顶技术。

近距离煤层厚硬顶板综放开采强矿压显现规律研究

针对厚硬顶板大采高综放工作面回采过程中强矿压的现象,以神东矿区某矿井近距离煤层厚硬顶板综放工作面为背景,通过现场实测和室内试验等方式,研究工作面矿压显现规律及覆岩破断特征。研究表明:(1)42105综放工作面老顶初次来压步距大,来压强度高,远超工作面支架额定工作阻力,工作面呈现出中部来压集中、强度高且较为频繁的特征;(2)近距离厚硬顶板下回采工作面时,重复采动下工作面覆岩破坏高度更大,尤其是上位关键层破断后带动下位关键层同时破断,并带动其控制的上覆岩层及上方采空区同步下沉,岩层载荷逐层向下传导至工作面,上下位关键层破断的协同作用,从而造成了工作面来压强烈。

龙岩市非煤矿山顶板事故分析与管理措施

顶板事故在非煤地下矿山事故中占比最多,顶板管理是非煤地下矿山安全管理的重点和难点。统计分析龙岩市2008—2023年共15a的顶板事故情况,总结非煤矿山顶板事故的特点。研究得出,矿井爆破工艺技术水平低及在大暴露空间下进行作业是顶板事故原因。提出改善措施,将中深孔爆破分段崩落采矿法代替空场法,但受到矿石价格影响,该方法成本高,当前可行性低;通过推广应用凿岩台车、撬毛台车等机械工具,严格控制井下采掘作业空间宽度和高度等措施,加强顶板管理,努力实现顶板零事故。