Stress spatial evolution law and rockburst danger induced by coal mining in fault zone

In order to explore the influence of coal mining disturbance on the rockburst occurring in fault zone, this research constructed a mechanical model for the evolution of fault stress, and analyzed the influence of the ratio of horizontal stress to vertical stress on the stability of fault, and the spatial distribution of the stress in fault zone as well as its evolution rule. Furthermore, the rockburst danger at different spatial areas of fault zone was predicated. Results show that: when both sides of the working face are mined out, the fault zone in the working face presents greater horizontal and vertical stresses at its boundaries but exhibits smaller stresses in its middle section; however, the ratio of horizontal stress to vertical stress is found to be greater at middle section and smaller at boundaries. As the working face advances towards the fault, the horizontal and vertical stresses of the fault firstly increases and then decreases; conversely,the ratio of horizontal stress to vertical stress keeps decreasing all the time. Therefore, if the fault zones are closer to the goaf and the coal wall, the stress ratio will be smaller, and the fault slip will be more prone to occur, therefore rockburst danger will be greater. This research results provide guidance for the rockburst prevention and hazard control of the coal mining in fault zone.     

Evolution and distribution of macroscopic gas channels in an overburden strata

The evolution of gas bearing channels in the roof, and their spatial distribution, was studied. A complete consideration of gas flow changes through the stress–strain changes in the roof near a working face is made. The theoretical abutment pressure distribution using displacement monitors and borehole visual recording instruments allow a theoretical analysis. Field test research determined the conditions for formation of macroscopic gas channels. These appear along the working face roof, normally distributed to it. These results show that the coal rock stratification becomes a macroscopic gas channel boundary if its deformation is less than the lower layer, or greater than the layer above it. At the same time the stability is greater than the distance from the roof for hanging dew conditions. The working face advances and the roof gas channels experience a cycle of development. Microscopic channels dominate the initial stage then macroscopic gas channels form, develop, and close. The evolution of the macroscopic channels depends on the ratio between the distances from the new compaction area in the goaf to the initial stress area in front of the working face. The amount of daily advance of the face also affects channel development. The experimental observations in one mining area showed that the main gas channels are located about 2 and 6.2 m above the lower surface of the roof and that they have an evolution period 7 to 11 days long.     

Effect of crack face contact on dynamic stress intensity factors for a hole-edge crack

In order to determine the dynamic stress intensity factors(DSIFs)for a single edge crack at the center hole of a finite plate under a compressive step loading parallel to the crack,the finite element method was employed to solve the cracked plate problem.The square-root stress singularity around the crack tip was simulated by quarter point singular elements collapsed by 8-node two-dimensional isoparametric elements.The DSIFs with and without considering crack face contact situations were evaluated by using the displacement correlation technique,and the influence of contact interaction between crack surfaces on DSIFs was investigated.The numerical results show that if the contact interaction between crack surfaces is ignored,the negative mode I DSIFs may be obtained and a physically impossible interpenetration or overlap of the crack surfaces will occur.Thus the crack face contact has a significant influence on the mode I DSIFs.     

易自燃煤层放顶煤开采工作面合理长度分析

以采空区自然发火危险为约束条件,用采空区场流方法(数值模拟)和自燃三带理论,结合实例,研究放顶煤开采工作面合理长度问题.得到工作面长度安全临界值与煤的最短自然发火期成正比关系.通过现场测定风量和采空区气体浓度分布,得到在当前工作面特定采空区流场环境下的自燃氧化带宽度和模型基础参数,数值模拟出不同工作面长度的采空区自燃氧化区宽度的变化关系;回归得到,在理论上,工作面长度与自燃氧化带宽度近似服从二次曲线关系.分析中给出了自燃安全判别量和自燃安全区间.     

复杂条件下上提蹬空工作面矿压显现特征研究

为了解决蹬空对巷道围岩变形影响严重等问题,针对张集矿1410（1）工作面复杂的地质条件,采用计算机数值模拟（UEDC）系统和现场工程实践相结合的方法,对工作面推进不同距离时上覆岩层垮落形态、初次来压步距、周期来压步距、液压支架受力以及巷道围岩的变形特征进行研究。研究表明：工作面老顶初次来压步距约为32 m左右,周期来压步距约为16 m左右。工作面液压支架所需支撑的最大岩层高度约为25m。在工作面每天正常推进8m的情况下,工作面压架的危险性较小。     

任意裂纹面荷载作用下界面断裂分析

为研究裂纹面上作用的荷载对裂纹稳定性的影响,本文基于比例边界有限元方法提出裂纹面作用有任意方向、任意大小面荷载的界面应力强度因子求解模型.界面裂纹具有复数形式的应力奇异性指数,在任意裂纹面荷载作用下其奇异应力场更为复杂.应用本模型,径向的位移和应力可解析求解,无需网格细分即可自动反映裂尖的应力奇异性.裂纹面上的任意荷载首先可分解成平行于裂纹面以及垂直于裂纹面的分量,并进一步分解成有限项幂函数的和.对每个幂函数荷载解析求解,基于线性叠加原理获得结构在全部荷载作用下的解.该模型对各向同性材料和各向异性材料均适用.文中通过板承受裂缝面荷载时的应力强度因子求解的多个算例对该模型进行了验证和应用,对板的几何尺寸和双材料参数进行了敏感性分析,并应用于重力坝坝踵界面裂缝在水压力作用下的应力强度因子求解.     

采场风流模拟实验台研制

本文从采场风流流动及瓦斯运移数学模型导出模型实验的相似准则,指导实验台设计。采用新型的实验材料和独特的采空区充填技术加工制做的多功能、组合式采场风流模拟实验台,具有设计结构合理、密封性能良好、重量轻、采空区充填带调整简单易行、风流流动及瓦斯涌出状态易控制、模型倾角任意可调等特点。预备实验证明,用该实验台研究采场风流流动及瓦斯运移规律是可行的。     

Elastodynamic stress intensity factor due to three-dimensional concentrated transient loading on the faces of a crack

The dynamic stress intensity factor for a semi-infinite crack in an otherwise unbounded elastic body is analyzed The crack is subjected to a pair of suddenly applied point loads on its faces at a distance l away from the crack tip The solution of the problem is obtained by superposition of the solutions of two simpler problems. The first of these problems is Lamb' s problem, while the second problem considers a half space with its surface subjected to the negative of the normal displacement induced by Lamb's problem in the range x>0. The latter is solved by means of integral transforms together with the application of Weiner-Hopf technique and Cagniard-de Hoop method. An exact expression is derived for the mode I stress intensity factor as a function of time for any point along the crack edge. Some features of the solution are discussed.     

Stress distribution and surrounding rock control of mining near to the overlying coal pillar in the working face

The occurrence of overlying coal pillar (OCP) exerts a strong effect on the stress and strain distribution of the surrounding rock in the stope. In this paper, the stress distribution characteristics are analyzed via the numerical calculation with the account of OCP presence or absence. In addition, this study revealed the joint effect of side pressure relief area of the goaf and stress concentration in OCP on the final stress distribution. Furthermore, the rules of abutment stress distribution affected by three influencing factors, namely horizontal-vertical distances between OCP and working face and buried depth of OCP, are analyzed. The functional model linking the peak stress of surrounding rock with the above influencing factors is developed. The field application of the above results proved that the rib spalling and deformation of a 2.95 m-high and 5.66 m-wide roadway could be efficiently controlled by rationally adjusting working states of the support, and adopting the hydraulic prop coordinated with the π type metal beam and anchor cable to strengthen the surrounding rock of working face and roadway, respectively. The proposed measures are considered appropriate to satisfy the safe operation requirements.     

SH波作用下圆形衬砌与直线形裂纹的相互作用

研究SH波入射情况下圆形衬砌结构与直线形裂纹的相互作用问题.在含有圆形衬砌弹性空间上,考虑仅含衬砌结构的情况,求出应力,取时间谐和的出平面线源载荷作用时的位移函数基本解作为Green函数,利用裂纹的"人工切割",在裂纹实际存在区域加置与所求应力大小相等、方向相反的应力,从而构造出裂纹.文中给出圆形衬砌与裂纹同时存在情况下的位移、应力表达式,求解衬砌边的动应力集中问题.最后利用算例讨论裂纹对衬砌结构的动应力集中系数的影响.     

Ground pressure and overlying strata structure for a repeated mining face of residual coal after room and pillar mining

To investigate the abnormal ground pressures and roof control problem in fully mechanized repeated mining of residual coal after room and pillar mining,the roof fracture structural model and mechanical model were developed using numerical simulation and theoretical analysis.The roof fracture characteristics of a repeated mining face were revealed and the ground pressure law and roof supporting conditions of the repeated mining face were obtained.The results indicate that when the repeated mining face passes the residual pillars,the sudden instability causes fracturing in the main roof above the old goaf and forms an extra-large rock block above the mining face.A relatively stable ‘‘Voussoir beam" structure is formed after the advance fracturing of the main roof.When the repeated mining face passes the old goaf,as the large rock block revolves and touches gangue,the rock block will break secondarily under overburden rock loads.An example calculation was performed involving an integrated mine in Shanxi province,results showed that minimum working resistance values of support determined to be reasonable were respectively 11,412 kN and 10,743 kN when repeated mining face passed through residual pillar and goaf.On-site ground pressure monitoring results indicated that the mechanical model and support resistance calculation were reasonable.     

正交异性双材料反平面界面裂纹分析

研究了正交异性双材料反平面界面裂纹问题。采用复合材料断裂复变方法,构造了特殊应力函数,通过求解一类偏微分方程组边界问题,推导出界面裂纹尖端附近的应力场、位移场及应力强度因子的表达式,确定了裂纹尖端应力场的奇异性,结果现实裂尖附近应力具有r^-1/2的奇异性,但没有振荡性。     

Study on fault induced rock bursts

In order to study the rules of rock bursts caused by faults by means of mechanical analysis of a roof rock-mass balanced structure and numerical simulation about fault slip destabilization, the effect of coal mining operation on fault plane stresses and slip displacement were studied. The results indicate that the slip displacement sharply increases due to the decrease of normal stress and the increase of shear stress at the fault plane when the working face advances from the footwall to the fault itself, which may induce a fault rock burst. However, this slip displacement will be very small due to the increase of normal stress and the decrease of shear stress when the working face advances from the hanging wall to the fault itself, which results in a very small risk of a fault rock burst.     

Pore pressure fluctuations of overlying aquifer during residual coal mining and water-soil stress coupling analysis

Three test models and a simulation model were constructed based on the prevailing conditions of the Taiping coalmine in order to analyze pore pressure fluctuations of an overlying aquifer during residual coal mining. As well, the relation between pore pressure and soil stress was evaluated. The model tests show the vibrations of pore pressure and soil stress as a result of mining activities. The simulation model tells of the response characteristics of pore pressure after mining and its distribution in the sand aquifer. The comparative analysis reveals that pore pressure and soil stress vibration are activated by unexpected events occurring in mines, such as collapsing roofs. An increased pore pressure zone always lies above the wall in front or behind the working face of a mine. Both pore pressure and vertical stress result in increasing and decreasing processes during movements of the working face of a mine. The vibration of pore pressure always precedes soil stress in the same area and ends with a sharp decline. Changes in pore pressure of sand aquifer are limited to the area of stress changes. Obvious changes are largely located in a very small frame over the mining face.     

大体积承台混凝土早期表面开裂控制措施

针对大体积混凝土浇筑时因水化热作用引起的早期表面开裂问题,对比分析浇筑温度、环境温度、保温材料以及位移约束条件4种因素对混凝土表面应力的影响程度.以宁波象山港公路大桥承台为实例建立有限元模型,选取6个开裂关键部位的节点,分析这些节点的应力数值在28d龄期内随4种影响因素变化的规律.模拟分析分层浇筑和水管冷却2种降温措施对于减小混凝土表面拉应力的作用.结果表明,混凝土表面拉应力与浇筑温度呈正比,与环境温度呈反比;保温层对承台表面中心部位拉应力的影响大于边缘部位;提高模板的刚度对抗裂有利;分层浇筑和水管冷却可以不同程度地改善表面开裂状况.     

Numerical analysis of gas emission rule from a goaf of tailing roadway

Targeting the problem of large amounts of gas emission from the goaf of the No.14201 working face in the Shaqu coal mine of Huajin Coking Coal Co. Ltd., we used a negative exponential function to describe the attenuation process of gas emission in goaf (the stable source) based on the principle of field flow. Equations of two-component flow (gas and air) and see- page-diffusion in a heterogeneous goaf flow field are solved by means of numerical simulation and fluid mechanics principles of air movement and gas distribution during gas emission from goaf. The results indicate that the air diversion volume has a negative, exponential relation with the volume of gas emitted from goaf to the working face and is clearly inversely related to gas concentration. We calculated the minimum amount of air diversion and distributed air volume in the tailing roadway required for safe production.     

Technology of back stoping from level floors in gateway and pillar mining areas of extra-thick seams简

According to the special requirements of secondary mining of resources in gateway-and-pillar goaf in extra-thick seams of Shanxi, this paper presents a technical proposal of back stoping from level floors. Numerical simulation and theoretical analysis are used to investigate the compaction characteristics of cavities under stress as well as an appropriate mining height of the primary-mining layer based on different mining widths and pillar widths. For Yangjian coal mine, the mining thickness of the first seam during back stoping from level floor is determined to be 3 m, which meets the relevant requirements. Gateway-and-pillar goaf of a single layer has a range of influence of 9 m vertically. If gateway-and-pillar goaf occurs both in 9-1 and 9-5 layers, the range is extended to within 11.2 m. When the mining width of a gateway is less than 2 m or larger than 5 m, the gateway-and-pillar goaf in the upper layer of the primary-mining seam can be filled in and compacted after stoping. When the working face is 2 m away from the gateway and pillar before entering into it and after passing through it, the coal body under the gateway and pillar is subjected to relatively high stress. During mining of the upper layer, moreover, the working face should interlock the goaf in primary-mining layer for 20 m.     

Numerical simulation of gas migration into mining-induced fracture network in the goaf

Gas extraction practice has been proven for the clear majority of coal mines in China to be unfavorable using drill holes in the coal seam. Rather, mining-induced fractures in the goaf should be utilized for gas extraction. To study gas migration in mining-induced fractures, one mining face of 10 th Mine in Pingdingshan Coalmine Group in Henan, China, has been selected as the case study for this work. By establishing the mathematical model of gas migration under the influence of coal seam mining, discrete element software UDEC and Multiphysics software COMSOL are employed to model gas migration in mining-induced fractures above the goaf. The results show that as the working face advances, the goaf overburden gradually forms a mining-induced fracture network in the shape of a trapezoid, the size of which increases with the distance of coal face advance. Compared with gas migration in the overburden matrix, the gas flow in the fracture network due to mining is far greater. The largest mining-induced fracture is located at the upper end of the trapezoidal zone, which results in the largest gas flux in the network. When drilling for gas extraction in a mining-induced fracture field, the gas concentration is reduced in the whole region during the process of gas drainage, and the rate of gas concentration drops faster in the fractured zone. It is shown that with gas drainage, the gas flow velocity in the mininginduced fracture network is faster.     

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.     

Roadway deformation during riding mining in soft rock

“Riding mining” is a form of mining where the working face is located above the roadway and advances parallel to it. Riding mining in deep soft rock creates a particular set of problems in the roadway that include high stresses, large deformations, and support difficulties. Herein we describe a study of the rock deformation mechanism of a roadway as observed during riding mining in deep soft rock. Theoretical analysis, numerical simulations, and on site monitoring were used to examine this problem. The stress in the rock and the visco-elastic behavior of the rock are considered. Real time data, recorded over a period of 240 days, were taken from a 750 transportation roadway. Stress distributions in the rock surrounding the roadway were studied by comparing simulations to observations from the mine. The rock stress shows dynamic behavior as the working face advances. The pressure increases and then drops after peaking as the face advances. Both elastic and plastic deformation of the surrounding rock occurs. Plastic deformation provides a mechanism by which stress in the rock relaxes due to material flow. A way to rehabilitate the roadway is suggested that will help ensure mine safety.