Rock burst risk evaluation based on equivalent surrounding rock strength

On-site investigations consistently show that the rock burst inherent to coal seams varies greatly with coal seam thickness. In this study, impact factors related to coal seam thickness and surrounding rock strength were analyzed and a corresponding rock burst risk assessment method was constructed. The model reflects the influence of coal seam thickness on the stress distribution of surrounding rock at the roadway. Based on the roadway excavation range, a stress distribution model of surrounding roadway rock is established and the influence of coal seam thickness on rock burst risk is analyzed accordingly. The proposed rock burst risk assessment method is based on the equivalent surrounding rock strength and coal seam bursting liability. The proposed method was tested in a 3500 mining area to find that it yields rock burst risk assessment results as per coal seam thickness that are in accordance with real-world conditions. The results presented here suggest that coal seam thickness is a crucial factor in effective rock burst risk assessment.     

Simulation of the relationship between roadway dynamic destruction and hypocenter parameters

Many factors can induce rock burst. Shock energy and shock distance are two key factors affecting rock burst. The 32101 roadway of the Xingcun coal mine, which has a tendency for rock burst, was used as an example. The dynamic module of Itasca's FLAC (Fast Lagrangian Analysis of Continua) 2D explicit finite-difference software was used to simulate the roadway's destruction. The vibration velocity and displacements of the rock surrounding the roadway were modeled for different shock energies and hypo-center distances. The simulation results indicate that the vibration velocity and displacement of rock surrounding the roadway have a quadratic relationship to the shock energy and a power law relationship to the distance of the hypocenter from the roadway. A dynamic view of the process was obtained from a series of "snap-shots" collected at 100 different time steps. This shows an isolat-ing "river" is first formed at the hypocenter. The region above the "river" is a low stress zone while below the "river" a high stress zone exists. This high stress zone surrounds the ribs of the roadway in a "double ear" pattern. Continuous and repeated action of the high stress in the "double ear" shaped zone destroys the roadway.     

Prediction of rock-burst-threatened areas in an island coal face and its prevention:A case study

The island coal face arises in coal mines with the purpose of preventing gas explosion or maintaining the balance between mining and tunneling. However, its particular stress conditions in the surrounding rock may increase the difficulty of stress control in the coal face and in its mining roadways, especially when the coal seam, the roof, and the floor have rock-burst propensities. The high energy accumulated in the island coal face and in its roof and floor will intensify rock-burst propensity or even induce rock burst,which further result in great casualties and financial losses. Taking island coal face 2321 in Jinqiao coal mine as a case, we propose a method for the prediction of rock-burst-threatened areas in an island coal face with weak rock-burst propensity. Based on the analysis of the movement of the overlying roof and characteristics of stress distribution, this method combined numerical simulation with drilling bits to ensure the prediction accuracy. The effects of coal pillars with different widths on the mitigation of stress concentration in the coal face and on the prevention of rock burst are analyzed together with the mechanism behind. Finally, corresponding measures against the rock burst in the island coal face are proposed.     

综放全煤平巷锚杆支护模拟试验研究

根据“巷道围岩松动圈支护理论”,以南屯矿３上 煤层综放工作面全煤平巷围岩条件为基础,对不同动压系数、侧压系数、锚杆支护参数条件下,锚杆支护巷道围岩应力分布、围岩变形及巷道破坏规律进行了模拟试验．试验证实,矩形煤巷顶板中存在一个卸压区,巷道两帮和角部区域围岩破坏严重,是支护的重点部位．锚网支护能有效控制采动压力影响下全煤巷道围岩的稳定性．试验得到的结论对于综放全煤巷道锚网支护设计和应用具有指导意义．     

Rock burst induced by roof breakage and its prevention

Based on the research on rock burst phenomenon induced by the breakage of thick and hard roof around roadways and working faces in coal mines, a criterion of rock burst induced by roof breakage (RBRB) was proposed and the model was built. Through the model. a method calculating the varied stresses induced by roof breakage in support objects and coal body was proposed and a unified formula was derived for the calculation of stress increment on support objects and coal body under different breaking forms of roof. Whilst the formula for calculating dynamic load was derived by introducing dynamic index K _d. The formula was verified in Huating Mine by stress measurement. According to the formula for stress increment calculating, the sensitivities of dynamic load parameters were further studied. The results show that the thickness and breaking depth of roof, width of support object are the sensitive factors. Based on the discussion of the model, six associated effective methods for rock burst prevention are obtained.     

Deformation and failure study of surrounding rocks of dynamic pressure roadways in deep mines

In order to understand the change rules of stress-displacement in surrounding rocks of dynamic pressure roadways in deep mines and to obtain a theoretical basis for analyses of roadway stability and designs of support,we established a coupling equation of adjacent rock strength,mining stress and supporting resistance on the basis of an elastic-plastic theory of mechanics.We obtained an analytical solution for stress and displacement distribution of elastic and plastic regions in surrounding rock of dynamic pressure roadway..Based on this theory,we have analyzed the changes in stress-displacement in elastic and plastic regions of surrounding rocks of dynamic pressure roadways in the Haizi Coal Mine.The results show that:1) radial and tangential stress change violently within the first 4 m from the inner surface of a roadway after excavation;radial stress increases while tangential stress decreases within a range of about 6 m from the inner surface of the roadway as a function of q3;2) radial and tangential stress increase with an increase in the mining pressure coefficient k;the increase in the rate of tangential stress is greater than that of radial stress;3) the radial displacement of the inner surface of roadways decreases with an increase in q3,provided that k remains unchanged.     

深部巷道围岩变形试验与数值模拟研究

为了研究深部软岩巷道的变形破坏特性,以淮南矿区某煤矿13-1煤回采巷道为例,在现场调查回采巷道工程概况的基础上,开展了室内深部回采巷道围岩变形特性相似模拟试验,并基于块体离散元法,建立了深部回采巷道围岩的数值模型,模拟了开挖过程中围岩的变形特性。相似模拟试验和数值模拟试验结果表明,深部巷道围岩的典型特征为:巷道底臌量两帮移近量顶板下沉量,巷道不同围岩受开挖扰动的位移影响范围不同,底板为3.5 m,顶板为2.45 m,两帮为5.5 m。     

超长"孤岛"综放面大煤柱护巷的数值模拟

基于兖矿集团兴隆庄4324超长“孤岛”综放工作面开采条件，采用离散元数值计算程序UDEC3．0，模拟研究了不同宽度煤柱护巷条件下巷道围岩的应力分布和变形特征，分析了不同宽度煤柱的承载状况和应力峰值区的位置．研究表明，采用20m大煤柱维护巷道，可以改善巷道围岩应力环境；煤柱的承载能力适应超长“孤岛”综放工作面顶板的活动规律；围岩变形量小；能够保障巷道的整体稳定性和有效断面．通过现场实测，讨论了大煤柱维护巷道的矿压显现规律和对巷道的良好维护效果．     

直墙拱形巷道围岩应力场分析

为得出直墙拱形巷道围岩应力分布规律,应用复变函数弹性理论推导了直墙拱形巷道围岩应力分布的解析表达式。对直墙拱形巷道边界的围岩应力和巷道水平线方向的围岩应力分布规律进行分析,并考虑直墙拱形巷道断面高宽比和侧压系数对其影响规律。研究表明：在不同巷道断面高宽比、侧压系数下,直墙拱形巷道围岩应力集中区域主要集中在直墙底部底角处、拱形顶板中点附近和底板中部3个位置。不同巷道断面高宽比下,直墙拱形巷道沿水平线的应力分布规律基本相同。侧压系数大于1时,采用巷道断面高宽比小于1较有利于巷道稳定;侧压系数小于等于1时,采用巷道断面高宽比大于1较有利于巷道稳定。     

Support technology for mine roadways in extreme weakly cemented strata and its application简

For the engineering geology conditions of bad mine roadway roof and floor lithology in extremely weak cemented strata, the best section shape of the roadway is determined from the study of tunnel surrounding rock displacement, plastic zone and stress distribution in rectangular, circle arch and arch wall sections, respectively. Based on the mining depth and thickness of the coal seam, roadway support technology solutions with different buried depth and thickness of coal seam are proposed. Support schemes are amended and optimized in time through monitoring data of the deformation of roadway, roof separation, I-beam bracket, bolt and anchor cable force to ensure the long-term stability and security of the roadway surrounding rock and support structure. The monitoring results show that mine roadway support schemes for different buried depth and section can be adapted to the characteristics of ground pressure and deformation of the surrounding rock in different depth well, effectively control the roadway surrounding rock deformation and the floor heave and guarantee the safety of construction and basic stability of surrounding rock and support structure.     

深部沿空切顶成巷围岩稳定性控制对策

基于沿空切顶成巷技术原理,以城郊煤矿深部工作面无煤柱开采为背景,综合运用力学分析﹑模拟计算和现场试验等方法,对深部切顶成巷围岩控制关键对策进行深入研究。结果显示：切顶留巷顶板在侧向形成短臂梁结构,降低了巷旁支护体所受压力,切缝范围内岩层垮落后碎胀充填采空区,使留巷顶板下沉量降低了约50%。采空区侧顶板为切顶巷道围岩变形的关键部位,需进行加强支护;深部切顶巷道实体煤帮塑性区范围大,通过煤帮锚索支护技术可将浅部锚杆承载层锚固在弹性区稳定煤体中;深部切顶成巷来压速度快、强度大,巷内单体支柱易造成冲击破断,采用高阻力液压支架巷内临时支护时可较好地抵抗深部强动压;巷旁刚性挡矸装置因无法适应深部围岩大变形而受压弯曲破坏,深部切顶巷道巷旁挡矸结构需实现一定的竖向让位卸压方可与顶底板协调变形。在研究的基础上提出恒阻锚索关键部位支护+可缩性U型钢柔性让位挡矸+巷内液压支架临时支护+实体煤帮锚索补强的深部切顶成巷联合支护技术,并进行现场工业性试验。现场监测结果表明：留巷围岩在滞后工作面约290 m时基本稳定,且稳定后各项指标满足下一工作面使用要求。     

Spatiotemporal evolution rule of rocks fracture surrounding gob-side roadway with model experiments

A series of plane-strain physical model experiments are carried out to study the spatiotemporal evolution rule of rocks fracture surrounding gob-side roadway, which is subjected to the pressure induced by the mining process. The digital photogrammetry technology and large deformation analysis method are applied to measure the deformation and fracture of surrounding rocks. The experimental results indicate that the deformation and fracture of coal pillars are the cause to the instability and failure of the surrounding rocks. The spatiotemporal evolution rule of the rock deformation and fracture surrounding gob-side roadway is obtained. The coal pillar and the roof near coal pillar should be strengthened in support design. The engineering application results also can provide a useful guide that the combined support with wire meshes, beam, anchor bolt and cable is an effective method.     

Similar simulation study on the deformation and failure of surrounding rock of a large section chamber group under dynamic loading

Large and super-large section chamber groups in coal mines are frequently affected by dynamic loads resulting from production activities such as roadway driving and blasting. The stability of the surrounding rock is poor, and it is difficult to control. In this paper, a similar simulation test was used to study the deformation and evolution laws of the surrounding rock of a triangle-shaped chamber group under different dynamic loads. The results showed that under dynamic loading, the vertical stress of the surrounding rock of the chamber group increased in an oscillatory form. The maximum stress concentration coefficient reached 4.09. The damage degree of the roof was greater than that of the two sides. The deformation of the roof was approximately 1.2 times that of the two sides. For the chamber closer to the power source, the stress oscillation amplitude of the surrounding rock was larger, and the failure was more serious. The force of the anchorage structure showed a phased increasing characteristic; additionally, the force of the anchorage structure on the adjacent side of the chambers was greater than that on the other side. This study reveals the deformation and failure evolution laws of the surrounding rock of large section chamber groups under dynamic loading.     

深部巷道围岩控制原理与应用研究

采用理论分析、数值模拟和现场试验的方法，研究深部巷道围岩稳定问题，认为深部巷道围岩控制的基本方法是提高围岩强度、转移围岩高应力以及采用合理的支护技术．提出了深部巷道围岩控制的基本技术和控制过程：1）应力转移降低巷道浅部围岩应力；2）采用高预紧力、大延伸量的高强度锚杆、锚索支护系统，强化锚固区围岩强度，提高巷道围岩自身稳定性；3）加强巷道两帮、底角支护，提高巷道最薄弱部位（两帮、底角）残余强度、提高巷道围岩的整体稳定性；4）应用高水速凝材料注浆加固破碎区，提高破碎围岩的完整性和力学参数．该研究成果已成功应用于工程实践．     

Rock burst mechanism analysis in an advanced segment of gob-side entry under different dip angles of the seam and prevention technology

In order to investigate the frequent occurrences of rock burst in gob-side entry during the mining process of the mining zone No. 7, the mechanical model of main roof of fully-mechanized caving mining before breaking was established by the Winkler foundation beam theory, and the stress evolution law of surrounding rock with different dip angles of the seam during the mining process was analyzed by using FLAC3 D. The results show that: with the dip angle changing from 45° to 0°, the solid-coal side of gobside entry begins to form an L-shaped stress concentration zone at a dip angle of 30°, and the stress concentration degree goes to higher and higher levels. However, the stress concentration degree of the coalpillar side goes to lower and lower levels; the influence range and peak stress of the abutment at the lateral strata of adjacent gob increase with dip angle decreasing and reach a maximum value at a dip angle of 0°, but the tailgate is not affected; the abutment pressure superposition of two adjacent gobs leads to stress concentration further enhancing in both sides of gob-side entry. With the influence of strong mining disturbance, rock burst is easily induced by dynamic and static combined load in the advanced segment of gob-side entry. To achieve stability control similar to that in the roadway, the key control strategy is to reinforce surrounding rock and unload both sides. Accordingly, the large-diameter drilling and high-pressure water injection combined unloading and reinforced support cooperative control technology was proposed and applied in field test. The results of Electromagnetic Emission(EME) and field observation showed that unloading and surrounding rock control effect was obvious.     

Comparative study of model tests on automatically formed roadway and gob-side entry driving in deep coal mines

Automatically formed roadway(AFR) by roof cutting with bolt grouting(RCBG) is a new deep coal mining technology. By using this technology, the broken roadway roof is strengthened, and roof cutting is applied to cut off stress transfer between the roadway and gob to ensure the collapse of the overlying strata. The roadway is automatically formed owing to the broken expansion characteristics of the collapsed strata and mining pressure. Taking the Suncun Coal Mine as the engineering background, the control effect of this new technology on roadways was studied. To compare the law of stress evolution and the surrounding rock control mechanisms between AFR and traditional gob-side entry driving, a comparative study of geomechanical model tests on the above methods was carried out. The results showed that the new technology of AFR by RCBG effectively reduced the stress concentration of the roadway compared with gob-side entry driving. The side abutment pressure peak of the solid coal side was reduced by 24.3%, which showed an obvious pressure-releasing effect. Moreover, the position of the side abutment pressure peak was far from the solid coal side, making it more beneficial for roadway stability. The deformation of AFR surrounding rock was also smaller than the deformation of the gob-side entry driving by the overload test. The former was more beneficial for roadway stability than the latter under higher stress conditions. Field application tests showed that the new technology can effectively control roadway deformation. Moreover, the technology reduced roadway excavation and avoided resource waste caused by reserved coal pillars.     

构造应力区巷道变形破坏特征及控制技术研究

水平构造应力对巷道围岩稳定有重要的影响,针对鹤壁九矿东总回风巷在锚网索喷＋u型钢支护难以保证巷道稳定的情况,通过相似材料模拟试验研究不同水平应力作用下锚注支护巷道围岩变形破坏和位移变化特征．试验表明,随着水平应力的增大,底板加强后,水平应力对顶板的作用明显,当水平载荷达到49MPa时有少量浆皮脱落,左肩部出现块状冒落,底板比较稳定,没有发生明显臌起,只出现少量横向裂隙,锚注支护结构能控制围岩变形．将试验结果在现场应用后,通过矿压观测,两帮的最大移近量为144mm,顶底板最大移近量为105mm,锚注支护提高了围岩的自承能力,能够维持巷道稳定,为类似地质条件下的巷道支护提供借鉴．     

Control technology and coordination deformation mechanism of rise entry group with high ground stress

Based on engineering practices of Wuyang Coal Mine, we carried out X-ray diffract researches on No. 3 coal; and the rocks of its roof and floor by XRD meter, and simulated the interactive effect of the surrounding rock deformation by FLAC^2D5.0 numerical simulation software under the condition of different tunneling method of multimine roadway in parallel. The internal structures of the surrounding rocks of 76 belt roadway were monitored by borehole observation instruments; and then, we analyzed the reason of failure and deformation of surrounding rocks of several rise entry, and proposed the technical measures for controlling interactive effect of several rise entry surrounding rock deformation at last. For the thickness seam rise roadway, two conclusions were drawn: one is that the co-deformation among roadway groups mainly reflect on that both shear failure and deformation in coal pillar among roadways have decreased the width of pillar core region and clamping action of coal pillar to roof strata, increased the actual span of roof strata, intensified the flexural failure of roof strata and prized the bed separation of roof deep rock strata. The other conclusion is that the factors controlling the interactive deformation among roadways is obvious when appropriate re-adjustment in construction sequence of the tunneling of multimine parallel roadways because the construction sequence among roadways also has great effects on deformation of the surrounding rock in roadway.     

Effect of faulting on coal burst——A numerical modelling study

Coal burst occurrence on roadways has always been a major concern in deep underground coal mines,especially under complex geological conditions. To evaluate the effect of faulting on coal burst, the stress concentration in the vicinity a reverse fault was analysed considering the geological history of the fault formation where high horizontal stresses led to the initiation and propagation of the reverse fault.Various in situ stresses and mechanical parameters of the fault, including the ratio of horizontal stress to vertical stress were used to analyse the state of fault. Numerical modelling was conducted using two and three dimensional distinct element models(UDEC and 3 DEC) based on a geotechnical conditions of an Australian underground coal mine. The formation process of reverse fault was simulated to evaluate the stress characteristics in the coal seam and the immediate roof and floor near the fault. The results show that, both the horizontal and vertical stress in footwall were higher than those in hanging wall after the formation of the reverse fault. The stress condition near fault was complicated due to complex geology in the coal measures, and the vertical stress peaked in the footwall at a distance of about 160 m from the fault. When a roadway was excavated, stress concentration occurred at both the roadway face and ribs, which reached as high as 38 MPa in the ribs at a depth of 500 m. This will significantly elevate the risk of dynamic instability of the roadway such as coal burst. The stress concentration zone in the footwall can be considered as a hazardous zone near the reverse fault. This study provides a general reference for analysis of roadway stability affected by faults.     

基于微震成像的采煤工作面应力异常监测

为了实现对深井采煤工作面的冲击地压灾害预防,采用微震走时成像技术,监测采煤工作面的应力异常.根据系统要求布置传感器台网,实现工作面全覆盖;采用层状模型分析地震波传播路径,计算地震波传播速度,利用子空间分阶段求解的方法进行反演,实现对监测区域的地震波走时层析成像;结合地震波速度和岩石所受应力的关系,达到研究采煤工作面应力异常的动态分布及变化特征的目的.试验结果表明：工作面推进时,煤层顶板高应力异常达到最大,工作面前方的高应力异常区动态变化范围较大,工作面后方存在较稳定的地震波低速异常,利用微震成像技术可以有效地监测地震波速度异常区域的范围及变化特征.