Predicting roof displacement of roadways in underground coal mines using adaptive neuro-fuzzy inference system optimized by various physics-based optimization algorithms

Due to the rapid industrialization and the development of the economy in each country, the demand for energy is increasing rapidly. The coal mines have to pace up the mining operations with large production to meet the energy demand. This requirement has led underground coal mines to go deeper with more difficult conditions, especially the mining hazards, such as large deformations, rockburst, coal burst, roof collapse, to name a few. Therefore, this study aims at investigating and predicting the stability of the roadways in underground coal mines exploited by longwall mining method, using various novel intelligent techniques based on physics-based optimization algorithms (i.e. multi-verse optimizer (MVO), equilibrium optimizer (EO), simulated annealing (SA), and Henry gas solubility optimization (HGSO)) and adaptive neuro-fuzzy inference system (ANFIS), named as MVO-ANFIS, EO-ANFIS, SA-ANFIS and HGSO-ANFIS models. Accordingly, 162 roof displacement events were investigated based on the characteristics of surrounding rocks, such as cohesion, Young's modulus, density, shear strength, angle of internal friction, uniaxial compressive strength, quench durability index, rock mass rating, and tensile strength. The MVO-ANFIS, EO-ANFIS, SA-ANFIS and HGSO-ANFIS models were then developed and evaluated based on this dataset for predicting roof displacements in roadways of underground mines. The results indicated that the proposed intelligent techniques could accurately predict the roof displacements in roadways of underground mines with an accuracy in the range of 83%–92%. Remarkably, the SA-ANFIS model yielded the most dominant accuracy (i.e. 92%). Based on the accurate predictions from the proposed techniques, the reinforced solutions can be timely suggested to ensure the stability of roadways during exploiting coal, especially in the underground coal mines exploited by the longwall mining.     

Case history of the response of a longwall entry subjected to concentrated horizontal stress

The National Institute for Occupational Safety and Health (NIOSH) Pittsburgh Research Laboratory (PRL), RAG Pennsylvania and Strata Control Technologies of Australia collaborated in an intensive study of ground behavior, reinforcement performance, and stress redistribution at the Emerald Mine in Southwestern Pennsylvania. The study site was a longwall tailgate subjected to a severe horizontal stress concentration. Field measurements indicated that the stresses applied to the study site nearly doubled during longwall mining, resulting in roof deformations extending to a height of 4.8 m (16 ft) above the entry. A computer simulation of the field site was conducted using FLAC-2D, incorporating a broad range of rock behaviors and failure mechanisms. Comparison between the measurements and the simulation showed that the model was able to capture the most significant aspects of the roof and support system behavior, particularly, the extensive slip along bedding that created a partially destressed “softened” zone in the immediate roof. The model also showed that supplementing the normal roof bolt support pattern with cable bolts would allow the entry to survive a further 20–25% increase in the applied horizontal stress. Such information could have very practical application to the design of roof support systems for coal mines.     

Mechanical behaviors of coal measures and ground control technologies for China's deep coal mines – A review

This paper reviews the major achievements in terms of mechanical behaviors of coal measures, mining stress distribution characteristics and ground control in China's deep underground coal mining. The three main aspects of this review are coal measure mechanics, mining disturbance mechanics, and rock support mechanics. Previous studies related to these three topics are reviewed, including the geomechanical properties of coal measures, distribution and evolution characteristics of mining-induced stresses, evolution characteristics of mining-induced structures, and principles and technologies of ground control in both deep roadways and longwall faces. A discussion is made to explain the structural and mechanical properties of coal measures in China's deep coal mining practices, the types and distribution characteristics of in situ stresses in underground coal mines, and the distribution of mining-induced stress that forms under different geological and engineering conditions. The theory of pre-tensioned rock bolting has been proved to be suitable for ground control of deep underground coal roadways. The use of combined ground control technology (e.g. ground support, rock mass modification, and destressing) has been demonstrated to be an effective measure for rock control of deep roadways. The developed hydraulic shields for 1000 m deep ultra-long working face can effectively improve the stability of surrounding rocks and mining efficiency in the longwall face. The ground control challenges in deep underground coal mines in China are discussed, and further research is recommended in terms of theory and technology for ground control in deep roadways and longwall faces.     

STUDY OF DOUBLE-CABLE-TRUSS CONTROLLING SYSTEM FOR LARGE SECTION COAL ROADWAY OF DEEP MINE AND ITS PRACTICE

 针对深井大断面煤巷围岩支护过程中出现的顶帮大变形控制难题,综合现场调研、数值模拟、理论分析、井下试验及现场实测,分析围岩变形破坏特征,提出高应力大断面巷道围岩控制系统--双锚索桁架,并对其组成结构、控制机制、支护优越性、应力场分布特征、关键支护参数等进行系统化研究,得出：(1) 深井大断面煤巷围岩变形特征为：移近量大、敏感系数高、变形具有持续性及破坏针对性强;(2) 新型双锚索桁架控制系统在巷道围岩中形成厚承载层和梯次锚固体结构,提高锚固岩层抗拉(剪)强度,保障巷道围岩和支护结构的稳定性;(3) 模拟得出双锚索桁架在岩层中形成垂直顶板(帮)均匀预应力带,预应力分散度低,影响范围集中于锚索锚固点区域3～5 m处;(4) 详细介绍井下运用双锚索桁架控制系统的一典型深井大断面煤巷成功实例。研究成果在邢东矿区获得全面应用,对类似条件工程的支护技术具有一定的理论意义和实用价值。     

采场顶板破断型震源机制及其分析

 作为一种区域、实时、动态监测手段,微震监测技术用于预测预报冲击矿压等地质灾害乃至防灾减灾完全可行,而不同震源震动机制的研究是微震法预测预报冲击矿压的前提和基础。采场顶板是影响煤矿冲击矿压发生的重要因素,在分析采场坚硬顶板断裂过程的基础上,建立坚硬顶板断裂震动的等效点源模型,并根据该模型用震动波理论分析坚硬顶板断裂的震动位移方程,揭示了坚硬顶板断裂的震源机制,并通过三河尖矿微震监测的坚硬顶板断裂信号验证分析结果的正确性。研究表明,采场顶板由于受源外介质的拉力作用,断裂时震源会产生波前向外传播的压缩波,震源处岩体破坏主要为张性拉伸破坏。研究结果可为顶板型冲击矿压的预测预报和防治提供理论依据。     

Distributions of airflow in four rectangular section roadways with different supporting methods in underground coal mines

A study has been carried out in four rectangular section roadways with different supporting methods in Yuwu Coal Company (a longwall mine), by measurements of airflow velocities in cross-section of the roadways. The asymmetrical distributions of airflow in each roadway section was obtained. The paper analyzes the low airflow velocity region of roadways through the drawing of the distributions of airflow in each roadway section. The supporting methods influence the low airflow velocity region around the roof and wall of roadways. It is shown that the low airflow velocity region increase with surface roughness of the roof and wall. The high airflow velocity region was located around the floor of the roadway with rough roof and wall. However, in the roadways with smooth roof and wall the high airflow velocity region was located around the center of section. The risk assessment should be carried out in the low airflow velocity region in the roadway with rough roof and wall. To ensure the safety of coal mining, higher volume of air intake or more smooth roof and wall of the roadways should be achieved in a dangerous zone.     

长壁孤岛工作面冲击失稳能量释放激增机制研究

煤矿开采中跳采形成的孤岛工作面由于容易产生应力集中，来压强度高，极容易发生冲击地压。基于唐山矿孤岛工作面的地质条件和周期来压步距的监测结果，通过数值分析的方法，研究孤岛工作面煤岩体能量释放的动态特征，揭示工作面前方能量释放激增机制，对比普通工作面和孤岛工作面能量场的区别，介绍冲击地压预警防治措施。数值模拟结果显示，长壁孤岛工作面回采时随着直接顶的随采随冒，采空区悬空面积的不断增大，使得老顶积聚大量的弹性能。若老顶发生周期性垮落，弹性能将瞬间释放，此时工作面和顺槽巷道极易冲击失稳。由研究结果可知，孤岛工作面周期来压时顶底板和煤层的能量激增可做为判断冲击失稳的前兆信息之一。因此，微震监测等手段可以根据此结论预测潜在的矿山动力灾害。针对老顶周期性断裂时积聚能量的突然释放规律，运用强制放顶、超前卸压孔、开切卸压槽和卸压爆破、煤层注水等技术可以提前释放煤层内积聚的弹性能，达到良好的冲击地压防治效果。     

淋涌水碎裂煤岩顶板煤巷破坏特征及控制对策研究

 针对淋涌水碎裂煤岩顶板煤巷支护过程中出现的围岩剧烈破坏难题,综合现场调研、煤岩试验、数值模拟、理论分析及井下试验与实测等方法,对其变形破坏机制、工字钢与锚杆(索)支护位移场的分布及煤巷动态破坏特征、顶板钻孔淋水量分区、新型防水锚固剂的锚杆(索)锚固力测试及淋涌水碎裂顶板控制对策进行系统化研究,主要研究内容及结论如下：(1) 淋涌水碎裂煤岩顶板的破坏主要是支护结构体的非整体性承载、锚杆(索)支护受钻孔淋水持续弱化失效以及顶板复合煤岩结构刚强度差异大而导致的离层综合作用的结果;(2) 研究新型防水树脂锚固剂,并通过井下淋涌水顶板锚杆(索)拉拔试验及支护后期锚索监测结果,检验防水锚固剂稳定性能;(3) 提出控制淋涌水碎裂顶板的“四位一体”控制对策,分析具体支护措施力学效应及保持顶板稳定性方面的作用;(4) 详细介绍井下运用“四位一体”综合控制系统的一典型淋涌水型碎裂煤岩顶板煤巷成功实例。研究成果可在霍州矿区进行推广应用,对类似条件巷道支护技术具有一定的理论和实用价值。     

晋城矿区地应力场研究及应用

 随着矿井开采深度与强度的不断增加,地应力对围岩变形与破坏的影响更加突出,在煤矿矿区进行地应力测量,并分析地应力场分布特征具有重要意义。在晋城矿区,采用小孔径水压致裂地应力测量装置,进行10个煤矿、62个测点的二维与三维地应力测量。实测数据表明：晋城矿区原岩应力以水平应力为主,构造应力占绝对优势,属于典型的构造应力场类型;地应力值属于中等水平;矿区东部与西部水平主应力方向变化较大,主要原因是受晋获褶断带的影响。基于实测数据,绘制晋城矿区地应力分布图;采用回归方法分析地应力随埋藏深度的变化规律;论述水平主应力与垂直主应力的比值同埋藏深度的关系,并与霍克–布朗包线进行比较。选择典型矿井,将地应力测量结果应用于巷道布置与支护设计,根据地应力场分布特征提出合理的巷道轴线布置方向,并在井下应用中得到验证。井下地应力测量为晋城矿区提供了可靠的基础数据,对指导矿区井田开拓、巷道布置与支护设计、采煤方法的选择等工程实践具有重要参考价值。     

Three-dimensional time-lapse velocity tomography of an underground longwall panel

Three-dimensional velocity tomograms were generated to image the stress redistribution around an underground coal longwall panel to produce a better understanding of the mechanisms that lead to ground failure, especially rockbursts. Mining-induced microseismic events provided passive sources for the three-dimensional velocity tomography. Surface-mounted geophones monitored microseismic activity for 18 days. Eighteen tomograms were generated and high-velocity regions correlated with high abutment stresses predicted by numerical modeling. Additionally, the high-velocity regions were observed to redistribute as the longwall face retreated, indicating that velocity tomography may be an appropriate technology for monitoring stress redistribution in underground mines.     

Assessment of roof stability in a room and pillar coal mine in the U.S. using three-dimensional distinct element method

This paper examines the effect of different geological and mining factors on roof stability in underground coal mines by combining field observations, laboratory testing, and numerical modeling. An underground coal mine in western Pennsylvania is selected as a case study mine to investigate the underlying causes of roof falls in this mine. Three-dimensional distinct element analyses were performed to evaluate the effect of different parameters, such as the variation of immediate roof rock mass strength properties, variation of discontinuity mechanical properties, orientations and magnitudes of the horizontal in-situ stresses, and the size of pillars and excavations on stability of the immediate roof. The research conducted in this paper showed that the bedding planes play an important role on the geo-mechanical behavior of roofs in underground excavations. Therefore, an appropriate numerical modeling technique which incorporates the effect of discontinuities should be employed to simulate the realistic behavior of the discontinuous rock masses such as the layered materials in roof strata of the underground coal mines. The three-dimensional distinct element method used in this research showed the capability of this technique in capturing the important geo-mechanical behavior around underground excavations.     

我国煤矿巷道围岩控制技术发展70年及展望

总结新中国成立70年来,我国煤矿巷道围岩控制领域取得的主要研究成果,涉及巷道围岩地质力学特性,围岩变形、破坏特征与机制,围岩控制理论及技术.介绍煤系沉积岩地层强度、煤岩体结构特征及煤矿井下地应力分布规律,采煤引起的采动应力场分布特征及对采动巷道围岩稳定性的影响.指出煤矿巷道围岩变形具有分阶段性、流变性和冲击性,巷道围岩...     

Innovation and future of mining rock mechanics

The 121 mining method of longwall mining first proposed in England has been widely used around the world.This method requires excavation of two mining roadways and reservation of one coal pillar to mine one working face.Due to considerable excavation of roadway,the mining roadway is generally destroyed during coal mining.The stress concentration in the coal pillar can cause large deformation of surrounding rocks,rockbursts and other disasters,and subsequently a large volume of coal pillar resources will be wasted.To improve the coal recovery rate and reduce excavation of the mining roadway,the 111 mining method of longwall mining was proposed in the former Soviet Union based on the 121 mining method.The 111 mining method requires excavation of one mining roadway and setting one filling body to replace the coal pillar while maintaining another mining roadway to mine one working face.However,because the stress transfer structure of roadway and working face roof has not changed,the problem of stress concentration in the surrounding rocks of roadway has not been well solved.To solve the above problems,the conventional concept utilizing high-strength support to resist the mining pressure for the 121 and 111 mining methods should be updated.The idea is to utilize mining pressure and expansion characteristics of the collapsed rock mass in the goaf to automatically form roadways,avoiding roadway excavation and waste of coal pillar.Based on the basic principles of mining rock mechanics,the“equilibrium mining”theory and the“short cantilever beam”mechanical model are proposed.Key technologies,such as roof directional presplitting technology,negative Poisson’s ratio(NPR)high-prestress constant-resistance support technology,and gangue blocking support technology,are developed following the“equilibrium mining”theory.Accordingly,the 110 and N00 mining methods of an automatically formed roadway(AFR)by roof cutting and pressure releasing without pillars are proposed.The mining methods have been applied to a large number of coal mines with different overburdens,coal seam thicknesses,roof types and gases in China,realizing the integrated mode of coal mining and roadway retaining.On this basis,in view of the complex geological conditions and intelligent mining demand of coal mines,an intelligent and unmanned development direction of the“equilibrium mining”method is prospected.     

Behaviors of overlying strata in extra-thick coal seams using top-coal caving method

Accidents such as support failure and excessive deformation of roadways due to drastic changes in strata behaviors are frequently reported when mining the extra-thick coal seams Nos.3e5 in Datong coal mine with top-coal caving method,which significantly hampers the mine's normal production.To understand the mechanism of strata failure,this paper presented a structure evolution model with respect to strata behaviors.Then the behaviors of strata overlying the extra-thick coal seams were studied with the combined method of theoretical analysis,physical simulation,and field measurement.The results show that the key strata,which are usually thick-hard strata,play an important role in overlying movement and may influence the mining-induced strata behaviors in the working face using top-coal caving method.The structural model of far-field key strata presents a "masonry beam" type structure when"horizontal O-X" breakage type happens.The rotational motion of the block imposed radial compressive stress on the surrounding rock mass of the roadway.This can induce excessive deformation of roadway near the goaf.Besides,this paper proposed a pre-control technology for the hard roof based on fracture holes and underground roof pre-splitting.It could effectively reduce stress concentration and release the accumulated energy of the strata,when mining underground coal resources with top-coal caving method.     

Auxiliary ventilation in mining roadways driven with roadheaders: Validated CFD modelling of dust behaviour

The production of dust when driving mining roadways can affect workers health. In addition, there is a decrease in productivity since Mine Safety regulations establish a reduction in the working time depending on the quartz content and dust concentration in the atmosphere.One of the gate roadways of the longwall named E4-S, belonging to the underground coal mine Carbonar SA located in Northern Spain, is being driven by an AM50 roadheader machine. The mined coal has a high coal dust content.This paper presents a study of dust behaviour in two auxiliary ventilation systems by Computational Fluid Dynamics (CFD) models, taking into account the influence of time. The accuracy of these CFD models was assessed by airflow velocity and respirable dust concentration measurements taken in six points of six roadway cross-sections of the mentioned operating coal mine.It is concluded that these models predicted the airflow and dust behaviour at the working face, where the dust source is located, and in different roadways cross-sections behind the working face.As a result, CFD models allow optimization of the auxiliary ventilation system used, avoiding the important deficiencies when it is calculated by conventional methods.     

Continuous and discontinuous stability analysis of the bell-shaped caverns at Bet Guvrin, Israel

The stability of two systems of bell-shaped caverns excavated some 1000 years ago at Bet Guvrin National Park is investigated. The caverns were excavated in a weak, anisotropic, and moderately discontinuous chalk. The cavern stability is considered based on two separate and independent methods: a continuum model framework—FLAC, used for stress analysis, and a discontinuous approach—block theory, used for critical key block analysis.The numerical stress analysis reveals that in the case of very large span openings, tensile fracture of intact rock may be responsible for instabilities, which may lead to global failure. Evidence of tensile rupture at margins of failed caverns is abundant at the Park.The discontinuous block theory analysis reveals that the moderate joint set spacing at Bet Guvrin, up to 45% of the roof area may be comprised of removable blocks. The removable keyblocks in the roof remain in place due to arching stresses, which develop through the roof material. The chalk at the roof can sustain the maximum loads in existing caverns, as predicted by the numerical stress analysis. However, local failures due to exceedingly high compressive stresses at the abutments or by tensile fracture at the roof, may lead to relaxation of arching stresses followed by keyblock displacement. Such a “mixed failure mode” process could eventually lead, over time, to global collapse. Indications that “mixed failure mode” processes are presently active in the studied caverns are substantiated by in-situ measurement of keyblock displacements.It is suggested that in weak and discontinuous rock environments where “mixed failure mode” processes may be active, long term stability evaluation should be based on both continuous and discontinuous stability analyses.     

超千米深井巷道围岩变形特征与支护技术

为解决超千米深井巷道支护难题,以新汶矿区深井巷道为工程背景,分析深部矿井地应力、围岩强度与结构等地质力学参数分布特征,超千米深井巷道围岩、支护体变形及破坏状况。采用UDEC数值模拟软件,研究不同支护方式与参数下超千米深井岩巷围岩变形、破坏特征与支护作用。基于实测与数值模拟研究结果,确定新汶华丰矿-1180回风大巷采用全断面高预应力、高强度锚杆与锚索及注浆联合支护加固方式。详细介绍-1180回风大巷支护井下试验,包括支护参数设计、支护材料、底板注浆锚索施工工艺及矿压监测结果。通过分析围岩位移、顶板离层及锚杆、锚索受力监测数据,评价回风大巷支护效果。井下试验表明:高预应力、高强度锚杆与锚索及注浆联合加固技术,能够有效控制超千米深井岩巷大变形,保持围岩长期稳定。最后,针对井下试验中存在的问题,提出改进意见。     

Validation of critical strain technique for assessing stability of coal mine intersections and its potential for development of roof control plans

Both room-and-pillar and longwall mining systems develop underground excavations whose stability must be ensured over their entire service life. Even though rock bolts have been extensively used as a support element in US coal mines for about 40 years, limited research has been conducted in quantifying its composite reinforcement effects. Recently, the authors suggested an approach to quantify the reinforcement effect of roof supports over a designated area based on critical failure strains in tension, compression and shear. This paper validates the critical strain technique (CST) using a case study and justifies the magnitude of selected critical strain by corroborating with the US roof fall statistics. Intersections are vulnerable to failure due to the larger exposed roof span and associated stress concentrations. Through numerical application of the CST to a case study, it was demonstrated that modifying the opening orientation and installing reinforcement at critical locations can help to improve the overall stability of intersections.     

Blast vibration damage to underground coal mines from adjacent open-pit blasting

A study was conducted to evaluate the effect of heavy blasting in open-pit coal mines on the stability of adjoining underground coal mine workings. Investigations were carried out at seven coal mines in India. Strata monitoring instruments, viz. borehole extensometers, convergence indicators, strain bars, stress capsules and load cells were installed in the roof and pillar. Monitoring of strata behaviour was carried out before and after the blasts. Arrangements were made to mount the transducers of seismographs in the roof and pillars to monitor vibration. Altogether, 202 production blasts were conducted and 622 vibration data were recorded.

The maximum peak particle velocity (PPV) recorded was 372.8 mm/s with the associated frequency of 78 Hz. At this magnitude of vibration, a coal block of 0.38 m³ detached from the roof. Minor damage in the form of loosened coal chips falling from the roof and the pillars was noticed at PPV level of 113 mm/s. Major damage was observed when the magnitude of PPV exceeded 181.9 mm/s. The damage is classified into three groups, viz. major damage, minor damage and no damage. The vibration levels in no damage zone are taken as safe level of vibration, The threshold value of vibration for the safety of underground workings is recommended based on the RMR of the roof rock.

It was also observed that the roof of underground roadways vibrated with 1.1–2.58 times higher amplitude of vibration compared to the pillars, The amplification was further higher at junctions. Monitoring of underground strata behaviour indicated, in all the mines, some amount of divergence between the roof and floor just after the blast, but, later on it was followed by convergence and most of the divergence that occurred was restored.     

厚泥岩复合顶板煤巷围岩控制技术研究

 针对首山一矿11061工作面运输平巷厚泥岩复合顶板强度低、无稳定承载结构、顶板下沉量大的问题,通过监测巷道围岩破坏及离层发育,统计巷道破坏具体形式,分析得出复杂应力条件下厚泥岩复合顶板巷道破坏的力学机制。基于普氏拱理论,结合现场具体支护和破坏状况,提出“预应力锚杆+锚索承载结构,配合原生裂隙区域注浆加固”的改进支护方案：预应力锚索(杆)形成的主、次承载结构协同作用,在两承载层间的泥岩顶板形成压缩区限制离层发展;布置倾斜锚索与垂直锚索,限制巷道顶帮角处围岩塑性区扩展,防止锚索锚固点所在岩层破断失去承载能力。依据塑性圈理论和数值模拟等手段,确定锚杆、锚索等具体支护参数,利用分区注浆加固泥岩强烈膨胀与松动破坏区域。数值模拟和现场工程实践的结果表明：与原支护方案对比,改进的支护方案巷道变形量减少约50%,巷道围岩完整程度明显提高,有效地控制了厚泥岩复合顶板变形与破坏。