Evaluation of roof cutting by directionally single cracking technique in automatic roadway formation for thick coal seam mining

Automatic roadway formation by roof cutting is a sustainable nonpillar mining method that has the potential to increase coal recovery,reduce roadway excavation and improve mining safety.In this method,roof cutting is the key process for stress relief,which significantly affects the stability of the formed roadway.This paper presents a directionally single cracking(DSC)technique for roof cutting with considerations of rock properties.The mechanism of the DSC technique was investi-gated by explicit finite element analyses.The DSC technique and roof cutting parameters were evaluated by discrete element simulation and field experiment.On this basis,the optimized DSC technique was tested in the field.The results indicate that the DSC technique could effectively control the blast-induced stress distribution and crack propagation in the roof rock,thus,achieve directionally single cracking on the roadway roof.The DsC technique for roof cutting with optimized parameters could effectively reduce the deformation and improve the stability of the formed roadway.Field engineering application verified the feasibility and effectiveness of the evaluated DSC technique for roof cutting.

Prediction of coal structure using particle size characteristics of coalbed methane well cuttings

Severely deformed coal seams barely deliver satisfactory gas production. This research was undertaken to develop a new method to predict the positions of deformed coals for a horizontal CBM well. Firstly, the drilling cuttings of different structure coals were collected from a coal mine and compared. In light of the varying cuttings characteristics for different structure coals, the coal structure of the horizontally drilled coal seam was predicted. And the feasibility of this prediction method was discussed. The result shows that exogenetic fractures have an important influence on the deformation of coal seams. The hardness coefficient of coal decreases with the deformation degree in the order of primary structural, cataclastic and fragmented coal. And the expanding-ratio of gas drainage holes and the average particle size of cuttings increase with the increase of the deformation degree. The particle size distribution of coal cuttings for the three types of coals is distinctive from each other. Based on the particle size distribution of cuttings from X-2 well in a coal seam, six sections of fragmented coal which are unsuitable for perforating are predicted. This method may benefit the optimization of perforation and fracturing of a horizontal CBM well in the study area.

Preparation and properties of a new cutting pick of coal shearers

Reliability and wear resistance of cutting picks play a significant role in coal mine exploitation with coal shearers.Tool bit separation,blade breaking,severe erosion of the cutting body and fatigue fractures are the main reasons for failure of cutting picks.We carried out carburization on a 30CrMnMo alloy to synthesize a new cutting pick material with improved mechanical properties and high wear resistance.The results indicated that carburization can effectively strengthen the surface of the 30CrMnMo alloy by forming a thick carburized layer and thus significantly improve the surface hardness and wear resistance.In addition,the excellent toughness of 30CrMnMo alloy as a substrate of cutting picks can prevent brittle ruptures and fatigue fractures under high impact stress conditions.The significant decrease in both frictional coefficient and rate of erosion of this carburized 30CrMnMo alloy suggests that this alloy is a potential material for cutting picks of coal shearers after rational carburization.

DISASTER ANALYSIS AND COUNTERMEASURES OF LAND SUBSIDENCE CAUSED BY COAL CUTTING IN CHINA

In recent years, many coal-producing countries have paid great atte ntion to the land subsidence caused by coal cutting. In China, because of the de nse population in coalfield areas, the land subsidence hazard is more serious. A fter a brief analysis on the mechanism of land subsidence, this paper gives a co mprehensive and systematical account on all kinds of hazards caused by the land subsidence in China. The study shows that land subsidence has endangered land, b uildings, traffic and communication lines, dykes and dams. It also causes damage to ecological and social environment. In order to lessen the hazard of land sub sidence, preventive measures should be taken to reduce the collapse amount, such as extraction with stowing, banded mining system, succession and coordination m ining system, or high-pressure mudflow between rock strata. Measures of reinfor cing or moving certain buildings should also be taken to reduce the destructive degree. In order to harness the subsidence land and bring them under control for farming, measures should be taken such as filling with spoil or fine breeze, ex cavating the deeper and covering the shallower land.

Prediction method for risks of coal and gas outbursts based on spatial chaos theory using gas desorption index of drill cuttings

Based on the evolution of geological dynamics and spatial chaos theory, we proposed the advanced prediction an advanced prediction method of a gas desorption index of drill cuttings to predict coal and gas outbursts. We investigated and verified the prediction method by a spatial series data of a gas desorption index of drill cuttings obtained from the 113112 coal roadway at the Shitai Mine. Our experimental results show that the spatial distribution of the gas desorption index of drill cuttings has some chaotic charac- teristics, which implies that the risk of coal and gas outbursts can be predicted by spatial chaos theory. We also found that a proper amount of sample data needs to be chosen in order to ensure the accuracy and practical maneuverability of prediction. The relative prediction error is small when the prediction pace is chosen carefully. In our experiments, it turned out that the optimum number of sample points is 80 and the optimum prediction pace 30. The corresponding advanced prediction pace basically meets the requirements of engineering applications.

Study on Vibration Cutting Mechanism of Bit for Ultrahard Coal Seam

This paper researches the vibration cuttiug mechanism for ultrahard coal seam by means of a selfmade test rig in the laboratory, when cutting tool was vibrating relatively to the coal specimen A new coal cutting method-vibration coal cutting method,was advanced’ The influence on main cutting force and unit energy consumption was investigated by changing the paramaters of vibratiou and cutting.The test data show that the vibration cutting method can reduce significantly the main cutting force and unit energy consumption at given vibration waveform and cutting object.

Numerical simulation of coal wall cutting and lump coal formation in a fully mechanized mining face

It is difficult to accurately calculate the lump coal rate in a fully mechanized mining face.Therefore,a numerical simulation of the coal wall cutting process,which revealed the crack expansion,development,evolution in the coal body and the corresponding lump coal formation mechanism,was performed in PFC2D.Moreover,a correlation was established between the cutting force and lump coal formation,and a statistical analysis method was proposed to determine the lump coal rate.The following conclusions are drawn from the results:(1)Based on a soft ball model,a coal wall cutting model is established.By setting the roller parameters based on linear bonding and simulating the roller cutting process of the coal body,the coal wall cutting process is effectively simulated,and accurate lump coal rate statistics are provided.(2)Under the cutting stress,the coal body in the working face underwent three stages—microfracture generation,fracture expansion,and fracture penetration—to form lump coal,in which the fracture direction is orthogonal to the cutting pressure chain.Within a certain range from the roller,as the cutting depth of the roller increased,the number of new fractures in the coal body first increases and then stabilizes.(3)Under the cutting stress,the fractured coal body is locally compressed,thereby forming a compact core.The formation and destruction of the compact core causes fluctuations in the cutting force.The fluctuation amplitude is positively related to the coal mass.(4)Because the simulation does not consider secondary damage in the coal,the simulated lump coal rate is larger than the actual lump coal rate in the working face;this deviation is mainly concentrated in large lump coal with a diameter greater than 300 mm.

Reliability analysis of the velocity matching of coal cutting and caving in fully mechanized top-coal caving face

The matching relationship between coal cutting and caving in fully mechanized top-coal caving face is analyzed in detail from the angle of reliability. The coupling equation of reliability is established correspondingly, and the mathematical equation of the coefficient of velocity matching of coal cutting and caving is obtained, which meets a certain reliability demand for making the working procedure of coal caving not influence coal cutting of coal-cutter. The results show that the relationship between the coefficient of the velocity matching and the reliability of coal cutting and caving system is linear on the whole when R <0.9. It is pointed out that different numerical value should be selected for different coal face according to different demand for reliability.

IMPACT COAL CUTTING AND TESTING

The paper analyses the stress characteristics in longwall face and its interaction with impact coal cutting, and puts forward the operation method for impact coal cotting. Similar material to the coal in particular mine was used to simulate the coal mass. Impact coal breaking test was performed on the test rig. The traveling pattern of the impact stress wave in coal and the dynamic response of impact parameters on coal property is analyzed.

Groundwater impact of open cut coal mine and an assessment methodology:A case study in NSW

Large scale open cut coal mining operations have significant impacts to groundwater in surrounding areas in both active and post-mining phases. The prediction of water inflows into a surface mine excavation is one of the many components involved in mine design phase. Groundwater performance also reacts to mining activities from the operational, economic and safety implications perspective. Under NSW planning legislation, as part of the comprehensive risk assessment, a groundwater impact assessment has to be conducted for a coal project to predict and mitigate the impacts in consideration of the government requirements. In this paper, the groundwater assessment modelling of mine pits was discussed in predicting of groundwater inflows and reviewing analytical and numerical approaches. A methodology of groundwater impact assessment for an open cut mine in NSW with a three-dimensional groundwater flow model Modflow Surfact demonstrated its functions in simulating the project's impacts on the groundwater regime. The key findings with mitigations are discussed and recommended in the paper to reduce impacts on groundwater and fulfil regulation requirements in NSW.

Model test of the cutting properties of a shearer drum

According to similarity theory, we carried out a dimensional analysis of the shearer drum correlation parameters and built similarity criteria. Based on these, similarity models of shearer drums were developed. Simultaneously, based on an estab- lished cutting testbed of the coal and rock, cutting tests of different pick arrangements of the drum models were carried out, where the compressive strength of the analogous cutting material was 2.48 MPa and the drum rotary speed 67.5 r/min. The variance, the mean values, maxima and mean maxima of the torque load were analyzed for different type drum models. Moreover, the relation-ships between the type of pick arrangements and the cutting lump coal percentage were studied. The results indicate that the load fluctuation of the sequence drum is larger than that of the punnett square drum in the cutting process and the lump coal percentage and economic benefits of the sequence drum are inferior to the punnett square drum. We conclude that the punnett square drum is superior to the sequence drum.

Ground pressure law of fully mechanized large cutting height face in extremely-soft thick seam and stability control in tip-to-face area

When stepped coal getting technology was applied to high seam mining working face, with field observations the following aspects of working face were analyzed based on the inherent conditions of extremely soft thick seam mined by Liangbei Mine, such as the brokenness and activity law of rock seam in the working face, the law of load-bearing of its supports, and the instability character of coal or rock in tip-to-face area. The following are the major laws. Pressure intensity of roof in high seam mining with extremely soft thick seam is stronger than one in slicing and sublevel-caving as a whole. But the greater crushing deformation of coal side makes pressure intensity of roof in the middle of working face be equivalent to one in sublevel-caving. In the middle of working face the roof brokenness has less dynamic load effect than roof brokenness in the two ends of working face. The brokenness instability of distinct pace of roof brings several load-bearings to supports. In condition of extremely soft thick seam, the ratio of resistance increment of supports in two ends of working face is obviously greater than that of supports in the middle. Most sloughing in coal side is triangular slop sloughing caused by shear slipping in high seam mining with extremely soft thick seam. Ultrahigh mining is the major reason for roof fall. Instability of coal or rock in tip-to-face area can be controlled effectively with the methods such as improving setting load of supports, mining along roof by reinforcing floor and protecting the immediate roof in time, and so on.

Research on Reliability of Desorption Indexes of Drilling Cuttings(K_(1)andΔh_(2)):A Case-Based on Pingdingshan Mining Region,China

To accurately predict the risk of coal and gas outburst and evaluate the reliability of desorption indexes of drilling cuttings(K_(1) andΔh_(2))in No.16 coal seam of Pingmei No.12 coal mine,two sets of coal samples were selected from the target coal seams for proximate analyses,methane adsorption/desorption tests,and desorption indexes of drilling cuttings tests.The results indicated that the desorption volume in the initial stage of desorption is large,and increases slowly in the later stage.The methane desorption volume of PMD1 and PMD2 coal samples accounts for 15.14%-18.09%and 15.72%-18.17%respectively in the first 1 min,and 43.92%-48.55%and 41.87%-52.25%respectively in the first 10 min in the 120 min desorption tests.Both K_(1) andΔh_(2) present power function relationships with methane pressure.Similarly,the power function relationships also can be found between the initial desorption characteristics(Q1 and Q4-5)and the methane pressure.Finally,the average relative error between the measured value and the calculated value of Q1 based on K_(1) is less than that of Q4-5 based onΔh_(2),which indicates that K_(1) is a more reliable index thanΔh_(2) to predict the risk of coal and gas outburst in the No.16 coal seam of Pingmei No.12 coal mine.

智能采煤机器人关键技术

采煤机是综采工作面的核心装备,研发智能采煤机器人是实现综采工作面智能化的关键。综合分析当前采煤机机器人化研究进程中的传感检测、位姿控制、速度控制、截割轨迹规划与跟踪控制等技术的研究现状,提出研发智能采煤机器人必须破解的“智能感知、位姿控制、速度控制、截割轨迹规划与跟踪控制、位-姿-速协同控制”五大关键技术,并给出解决方案。针对智能感知问题,提出了构建智能感知系统思路,给出了智能采煤机器人智能感知系统的架构,实现对运行状态、位姿、环境等全面感知,为智能采煤机器人安全、可靠运行提供保障;针对位姿控制问题,提出了智能PID位姿控制思路,给出了改进遗传算法的PID位姿控制方法,实现了智能采煤机器人位姿精准控制;针对速度控制问题,提出了融合“力-电”异构数据的截割载荷测量思路,给出了基于神经网络算法的截割载荷测量方法,实现了截割载荷的精准测量;提出牵引与截割速度自适应控制思路,给出了人工智能算法牵引与截割速度决策方法和滑模自抗扰控制的牵引与截割速度控制方法,实现了智能采煤机器人速度精准自适应控制;针对截割轨迹规划与跟踪控制问题,提出了截割轨迹精准规划思路,给出了融合地质数据和历史截割数据的截割轨迹规划模型,实现了截割轨迹的精准规划;提出了截割轨迹精准跟踪控制思路,给出了智能插补算法的截割轨迹跟踪控制方法,实现了智能采煤机器人截割轨迹高精度规划与精准跟踪控制;针对“位-姿-速”协同控制问题,提出了“位-姿-速”协同控制参数智能优化思路,给出了基于多系统互约束的改进粒子群“位-姿-速”协同控制参数优化方法,实现了智能采煤机器人智能高效作业。深入研究五大关键技术破解思路,有利于加快推动研发高性能、高效率、高可靠的智能采煤机器人。

开采保护层与预抽煤层瓦斯防突效果分析

为比较开采保护层与预抽煤层瓦斯防突效果,以1124(3)运顺开采保护层段和预抽煤层瓦斯段煤巷掘进为试验对象,统计了试验地点煤巷掘进期间残余瓦斯含量、钻屑瓦斯解吸指标K1、钻屑量等防突指标,采用假设检验方法推断了各防突指标是否有差别,分析了开采保护层段和预抽煤层瓦斯段各防突指标产生差别的原因,验证了开采保护层区域防突措施比预抽煤层瓦斯区域防突措施更加安全可靠。

极近距离煤层开采无煤柱自成巷控制方法研究

极近距离煤层传统长壁开采,受上层遗留煤柱和采空区垮落等因素的影响,下煤层开采过程中应力环境复杂、矿压显现剧烈,易诱发巷道围岩大变形。为解决上述问题,提出了极近距离条件下巷道定向切顶–约束高强支护无煤柱自成巷控制方法。通过顶板定向预裂切顶,主动改变顶板悬臂结构,切断采空区向巷道顶板的应力传递。充分利用矿山压力和岩体碎胀特性,取消煤柱留设,结合高强支护加强巷道顶板整体性,共同实现切顶自成巷。建立了极近距离煤层开采覆岩结构模型,计算了下煤层切顶自成巷巷旁支护阻力。以典型极近距离煤层为工程背景,开展了不同开采方法的数值试验对比研究,结果表明,提出的自成巷控制方法使巷道围岩应力降低59.8%,巷道顶板变形减少70.8%,并明确了极近距离煤层开采无煤柱自成巷控制机理。在此基础上,开展了典型极近距离煤层工程设计及现场应用研究,结果表明该方法有效降低了矿压显现程度,保证了自成巷的安全稳定控制。

突出煤层分层切削钻孔瓦斯释放特征及应用研究

【目的】突出煤层钻进过程中的喷孔瓦斯超限是威胁矿井高效生产的安全隐患,分层切削钻进方法有助于在孔内削弱喷孔瓦斯压力,但分层切削形成的梯形钻孔周围瓦斯释放特征不明,限制了分层切削钻具结构设计和应用效果。【方法】以不同层间距、层厚差的分层切削钻孔为研究对象,建立数学模型分析钻孔周围瓦斯流动规律,并定量描述了分层切削钻孔瓦斯流量与层间距、层厚差之间的关系,在此基础上,通过数值模拟分析了分层切削钻具瓦斯释放调控机制,优化了分层切削钻具结构,并开展了现场钻进工业性试验。【结果和结论】结果表明:(1)多次切削成孔方式使钻孔的揭露面积逐渐增大,有效控制了瓦斯释放面积,进而调控了瓦斯释放流量,通过合理设计钻孔层厚差Hj与层间距Li,能够将瓦斯释放流量降低18.3%以上。(2)在一定层间距范围内,双层切削钻具调控效果将优于三层切削钻具,直径为63.5 mm刻槽阻尼钻杆在推力140 kN和扭矩4600 N·m作用下,最小安全系数为3.009,满足强度设计要求。(3)优选双层切削钻具,其揭露直径73 mm,终孔直径113 mm,层间距0.8 m,通过工业性试验,钻遇高压瓦斯富集区时,孔口瓦斯体积分数降低了37.7%,孔口瓦斯体积分数均未超过0.5%。表明分层切削钻具调控钻孔周围煤体瓦斯释放量、削弱瓦斯释放强度的作用显著,为预防钻孔喷孔瓦斯超限问题提供了新的解决思路。

采煤机截割部低照度图像的边缘检测技术

针对井下低照度环境下采煤机截割部边缘检测任务中存在的边缘缺失、细节模糊等问题,提出一种基于分数阶微分的边缘检测Lif算法。首先采用更大的检测模板尺寸,根据Grünwald-Let-nikov分数阶定义构造最初的分数阶掩膜算子;然后根据Pascal三角形理论确定掩膜算子上各位置的权重系数,并将掩膜算子扩展到4个不同方向;最后将得到的掩膜算子与图像进行卷积,利用图像的局部特征信息对每个方向的微分结果进行后处理。结果表明:(1)在进行多个不同场景的井下低照度图像上的实验时,Lif算法可以更全面地获取图像中不同方向上的边缘信息,在处理低照度图像时具备更强的抗噪性能,并且提取的边缘线条比其余边缘检测算法更加清晰、完整,保留了更多的纹理细节信息。(2)在客观指标评价的对比上,与基于分数阶灰色系统模型的边缘检测算法以及改进的分数阶Sobel边缘检测算法相比,Lif算法在Entropy指标上分别提高了43%、11%,AG指标上分别提高了23%、23%,SSIM指标上分别提高了152%、6%。表明Lif算法在进行采煤机截割部的边缘检测任务时更具优势,研究对井下设备工作运行时的安全性和可靠性提升具有重要意义。

基于红外热像和振动信号的煤岩识别实验研究

针对现有煤岩识别技术存在的难以实际应用、易受信号干扰、成本高和实现复杂等问题,通过理论分析煤岩截割产热与煤岩硬度的关系,证明通过红外热像获取的截割温度变化来进行煤岩识别的合理性;搭建了掘进机截齿截割煤岩试验台,对不同硬度的普通煤层、煤岩交界处及中砂岩层进行长时间截割试验,通过红外热像仪和振动传感器分别获取截割温度和截割头振动信号并分析其变化规律。研究结果表明:①随着截割时间增加,截割温度逐渐升高;煤岩硬度越高,截割温度越高,且截割温度上升速率越快;在截割起始阶段无法通过截割温度识别煤岩,但在稳定截割时可根据截割温度特性识别煤岩。②截割头振动强度随着煤岩硬度增大而变大,但不随截割时间增加而产生明显变化,因此可弥补在截割起始阶段无法通过截割温度识别煤岩的不足。③通过单一截割温度或振动强度不能对煤岩进行准确识别,因此可在截割起始阶段和频繁出现闪温时通过振动强度来识别煤岩,而在截割稳定阶段通过红外热像获取的温度来识别煤岩。

大采高综采工作面切顶留巷矸石帮变形控制技术研究

为解决厚煤层大采高综采工作面切顶留巷矸石帮围岩控制难题,首先利用理论分析建立了不同挡矸支护条件下矸石帮位移变化的力学公式,以此为基础提出矸石帮变形控制双策略,减弱矸石帮变形压力和增强矸石帮的抗变形能力;其次利用现场实验设计两种类别共4组挡矸支护方案,探讨不同支护方案的矸石帮控制效果,验证理论研究成果。结果表明:①增强矸石帮侧顶板支护强度,能减弱矸石帮变形压力;②增架卡兰个数、增加卡兰预紧力、增加卡兰个数、增强U型钢之间的摩擦力等能增加U型钢滑移初始滑移应力,增强矸石帮的抗变形能力;③挡矸支护控制效果为:2副卡兰+单体支柱<2副卡兰+单元支架<2副卡兰+单元支架+呛柱<3副卡兰+单元支架。该研究可为同类条件下切顶留巷矸石帮变形控制提供参考。