近距离采空区下煤层开采矿压显现特征研究

以湘桥煤矿10#煤层开采为工程背景,对上覆采空区的底板破坏情况以及下伏煤层开采的顶板变形进行了理论分析,采用UDEC数值模拟软件对比分析了单一煤层开采与近距离采空区下煤层开采的矿压显现规律。结果表明:相较于单一煤层开采,近距离采空区下煤层开采支承压力应力集中程度更高,其超前支承压力强度更大;同时,由于近距离采空区下煤层开采属于重复采动,下煤层顶板岩层破坏较单一煤层开采更为严重,采场支护强度设计必须考虑上部采空区的影响。因此,在进行近距离采空区下煤层开采时必须采取加强下伏煤层开采超前支护、提高采场液压支架支护强度等措施,以保证近距离采空区下煤层开采顶板的有效管理和安全回采。

近距离煤层群下煤层开采矿压显现规律研究

本文通过实测山西省某矿区某煤矿的近距离煤层群采空区下煤层开采的矿压显现规律,理论研究了了上煤层采空区与遗留煤柱对下煤层回采工作面矿压显现的影响,并对下煤层回采工作面初次来压、周期来压步距及工作面液压支架随工作面推进过程的变化进行了实测分析。结果表明,通过滑移场理论和极限平衡理论推导得到的采动底板破坏公式,能够较好的结合具体的煤层及底板岩层条件进行底板破坏深度及范围的计算,另外相比较覆岩中无采空区下测区,采空区下测区周期来压较混乱,强度不同的周期来压交替出现,强度较大的周期来压时压力增加过程短,来压较突然,且强度较大的周期来压对应的来压步距较短。该研究有利于为了进一步认识近距离煤层群采空区下回采工作面的矿压显现规律。

近距离下煤层开采巷道布设及支护分析

以近距离下煤层开采巷道布设及支护为对象开展探究。结合具体工程实际,在分析下煤层开采巷道布设的基础上,对巷道分段支护设计开展分析总结,并对其实际应用效果做出分析,希望能为其他矿井相似工程的开展提供借鉴和参考。

铁路下煤层开采后所带来的影响及防范措施

针对矿区铁路专用线多建在煤田和采空区上方 ,对专用线行车安全和事故预防进行分析 ,确保专用线运输畅通。

相邻煤层开采巷道支护技术的分析研究

针对相邻煤层存在的煤层间距小,开采条件困难,且因上煤层开采过程中底板煤岩层受到破坏,导致下煤层顶板在开采前损坏,造成下煤层回采巷道维护困难的难题,通过对相邻煤层开采条件研究,并对上煤层开采过程中工作面顶板稳定性分析,以及对上煤层预留煤柱载荷对地板的压力分布研究,确定下煤层工作面顶板易出现局部应力过载,产生局部顶板破坏。最后确定了下煤层回采巷道合理内错方式。

近距离下煤层回采巷道支护效果监测分析

镇城底矿28102工作面的上部有两个工作面,分别为22108和22201工作面,两个工作面都已经开采。通过分析巷道围岩控制技术作用原理,结合巷道实际情况,确定下煤层回采巷道采用锚网索工字钢棚联合支护形式。为了分析28102工作面回采后巷道支护效果,采用现场实测的方法进行研究。从观测的结果可以看出,两断面中顶底板最大移近量为巷道断面尺寸的7.4%,两帮最大移近量为巷道断面尺寸的2.4%,巷道表面变形较小。所有的监测测点锚杆的受力变化幅度较小,说明锚杆的受力比较稳定,支护参数选择合理。可见采用锚网索加工字钢棚的支护方式能够对巷道的围岩进行很好的控制,保证巷道的安全正常使用。

Geotechnical risk management to prevent coal outburst in room-and-pillar mining

A coal outburst is a severe safety hazard in room-and-pillar mining under deep cover. It is more likely to occur during pillar retreating. Multi-seam mining dramatically increases the risk of coal outburst within the influence zones created by remnant pillars and gob-solid boundaries. Though coal outburst is generally associated with heavy loading of coal pillars,its occurrence is difficult to predict. Risk management provides a proactive tool to minimize coal outburst in room-and-pillar mining under deep cover. Risk assessment is the first step in identifying and quantifying outburst risk factors. The primary risk factors for coal outburst are overburden depth,roof and floor strength,geological anomalies,mining type,multi-seam mining,and panel width. A risk assessment chart can be used to proactively screen out mining sections with high risk of coal outburst for further analysis. Gob-solid boundaries and remnant pillars are critical factors in evaluation of the coal outburst risk of multi-seam mining. Risk identification,risk assessment,geologic influence mapping,geotechnical evaluation,risk analysis,risk mitigation,and monitoring are essential elements of coal outburst risk management process. Training is an integral part of risk management for risk identification and communication between all the stakeholders including management,technical and safety personnel,and miners.

Quantification and assessment of fault uncertainty and risk using stochastic conditional simulations

The effect of geological uncertainty on the development and mining of underground coal deposits is a key issue for longwall mining, as the presence of faults generates substantial monetary losses. This paper develops a method for the conditional simulation of fault systems and uses the method to quantify and assess fault uncertainty. The method is based on the statistical modelling of fault attributes and the simulation of the locations of the centres of the fault traces. Fault locations are generated from the thinning of a Poisson process using a spatially correlated probability field. The proposed algorithm for simulating fault traces takes into account soft data such as geological interpretations and geomechanical data. The simulations generate realisations of fault populations that reproduce observed faults, honour the statistics of the fault attributes, and respect the constraints of soft data, providing the means to thereby model and assess the related fault uncertainty.

Mining-induced variation in water levels in unconsolidated aquifers and mechanisms of water preservation in mines

Phreatic water resources are widely found in thick unconsolidated surface layers in western China, where water levels respond sensitively and quickly to large-scale underground mining in conjunction with shallow coal seams. Longwall face #32201 of the Bulianta Coal Mine, in the Shendong coalfield was selected as an industrial trail base, where field observations on ground-water levels were conducted when the working face was below a water-rich area. The space-time variation in the behavior of un-consolidated water levels in response to underground mining and its relation with of advance were observed through the field trials. The basic conditions for water preservation in mines are presented and the mechanisms of water preservation in mining analyzed, given the geological condition of two key strata and a severely weathered layer buried in the overburden. The field trails show that water preservation in mining shallow coal seams can be successful under suitable conditions, providing new technology for envi-ronmental protection in the desert coalfields of northwestern China.

Study on effects of longwall mining on the underground water

It is very important for secure mining under water bodies to study the effects of Iongwall mining on the underground water. In order to study this problem, piezometers for monitoring underground water levels were established in an American coalmine. Large amounts of pre-mining and post-mining monitoring data were collected. Based on the data the effects of Iongwall mining on the underground water was studied. The results demonstrate that when the piezometer monitoring wells have an interburden thickness less than 72.7 m, the groundwater level decreases immediately to immeasurable levels and go dry after undermining. The height of the fractured zone in is 72.7-85.3 m in this geological and mining conditions. The results also show that the calculated value of fractured zone by the empirical formulae used in China is smaller than the actual results. Therefore, it is not always safe to use them in analysis of mining under water bodies.

Characteristics and stability of slope movement response to underground mining of shallow coal seams away from gullies

Underground pressure is abnormal during mining of shallow coal seams under gullies. We studied gully slope movements, subject to underground mining, with physical simulation and theoretical analysis. The rules disclose that the slope rock slides horizontally in response to mining in the direction of gullies and rotates reversely with the appearance of a polygon block in mining away from gullies. We focused our attention on the case of mining away from a gully. We built a mechanical model in terms of a polygon block hinged structure and investigated the variation of horizontal thrust and shear force at the hinged point in relation to the rotation angle under different fragmentations. The Sliding-Rotation instability conditions of the polygon block hinged structure are presented based on the analyses of sliding instability and rotation instability. These results can serve as a theoretical guide for roof control during mining away from gullies in a coalfield defined by gullies.

Underground mining of thick coal seams

This paper reviews underground mining methods for total thickness of a thick coal seam in single lift （TI＇rCSSL）. Review shows the required engineering for extraction of thick seams needs to be fitted with thickness of the seam, behavior of rock-mass and surrounding stress conditions for efficient mining. Variants of TI＇rCSSL are able to extract a maximum 10-12 m thickness only. An improvement in bending moment of the overlying coal band in longwall top coal caving （LTCC） provides better under-winning opportunity for the roof coal band. An acceptable limit of 25 MPa compressive strength of coal for the success of LTCC may be increased under favorable geo-technical conditions. Bord and pillar in India adopted induced caving of roof coal band for single lift depillaring of total thickness （SLDTr） of a compe- tent thick coal seam developed along floor. Case studies are given to arrest the adverse effects of extrac- tion height on pillars.

Pressure-relief effect of coal rock body of long distance lower protective seam mined based on FLAC^(3D)

According to the specific geological condition, analyzed the stress distribution of the overlying strata, the displacement of pressure released seam, thickness variation and the distribution of plastic zones by FLAG3D software to simulate mining of the long-distance lower protective seam. The research results show that the distribution of vertical stress appears as a ＂Double-hump＂ within the pressure-relief range of the protected coal seam and the swelling deformation curve of coal bodies takes an ＂M＂ shape. The swelling is divided into initial swelling, swelling increase and swelling compression stability. The maximum swelling ratio of the pressure released seam is 1.84%, protection angle of the lower protective coal seam along the strike direction is about 55°, protection angle below the dip direction is about 50°, protection angle above the dip direction is about 55°, and the coal seam compression zone resembles a ＂U＂ shape.

Measurement of shear movements in the overburden strata ahead of longwall mining

An underground coal mine located in New South Wales has a target coal seam located 160-180 m deep directly below a 16-20 m thick conglomerate unit that has been associated with significant periodic weighting events on the Iongwall face. As part of the investigations to better understand the causes of periodic weighting at the mine. inclinometers capable of measuring horizontal shear movements through the full section of the overburden strata were installed ahead of mining at two locations approximately 1 km apart above the centre of two iongwall panels. These inclinometers were monitored as the longwall approached each site. This paper presents the details of the installation, the results of the inclinometer monitoring at both sites, and the insights that these measurements provide for overburden behaviour about longwall panels. Horizontal shear movements were observed to develop on shear horizons that correlate closely across the two sites suggesting a mechanism that is consistent across a large area of the mine. Shear movements were observed to develop on a single horizon near the top of the conglomerate strata that was mobilised almost immediately after initial formation of the longwall goal at a distance of 425 m ahead of the longwall face.