Permeability evolution and gas flow in wet coal under non-equilibrium state:Considering both water swelling and process-based gas swelling

Accurate knowledge of gas flow within the reservoir and related controlling factors will be important for enhancing the production of coal bed methane.At present,most studies focused on the permeability evolution of dry coal under gas adsorption equilibrium,gas flow and gas diffusion within wet coal under the generally non-equilibrium state are often ignored in the process of gas recovery.In this study,an improved apparent permeability model is proposed which accommodates the water and gas adsorption,stress dependence,water film thickness and gas flow regimes.In the process of modeling,the water adsorption is only affected by water content while the gas adsorption is time and water content dependent;based on poroelastic mechanics,the effective fracture aperture and effective pore radius are derived;and then the variation in water film thickness for different pore types under the effect of water content,stress and adsorption swelling are modeled;the flow regimes are considered based on Beskok’s model.Further,after validation with experimental data,the proposed model was applied to numerical simulations to investigate the evolution of permeability-related factors under the effect of different water contents.The gas flow in wet coal under the non-equilibrium state is explicitly revealed.

Effect of suppressing dust by multi-direction whirling air curtain on fully mechanized mining face

A combined method of numerical simulation and field testing was adopted in this study in the interest of solving the problem of hard to control high concentrate dusts on a fully mechanized mining face.In addition,the dust suppression effect of a multi-direction whirling air curtain was studied in this paper.Under the influence of the wall attachment effect,the compressed air which blows out from the two-phase or three-phase radial outlets on the generator of the air curtain can form a multi-direction whirling air curtain,which can cover the whole roadway section of a fully mechanized mining face.The traditional method of controlling dust is a forcing system with exhaust overlap which has the major disadvantage of lacking a jet effect and consequently results in poor dust control.It is difficult to form the air flow field within the range of L_p5Sr^(1/2).However,due to the effect of this novel system,the radial airflow can be turned into axial airflow allowing fresh air to flow through the length of the heading.The air flow field which is good at controlling dust diffusion can be formed 12.8 m from the heading face.Furthermore,the field measurement results show that before the application of a multi-direction whirling air curtain,the dust concentration is 348.6 mg/m^3 and 271.4 mg/m^3 respectively at the roadway cross-section measurement points which are 5 m and 10 m from the heading face.However,after the application of the multi-direction whirling air curtain,the dust concentration is only 61.2 mg/m^3 and 14.8 mg/m^3,respectively.Therefore,the dust control effect of a multi-direction whirling air curtain is obvious.

Breaking process and mining stress evolution characteristics of a high-position hard and thick stratum

Based on the boundary support conditions of overlying high-position,hard and thick strata,a Winkler foundation beam mechanical model was built.Computational expressions for the characteristics and position of the bending moment for high-position,hard and thick strata were constructed by theoretical analysis,and the initial breaking position of high-position,hard and thick strata was also analyzed.The breaking process and evolution law of mining stress in high-position,hard and thick strata were studied by similar material simulation tests.Studies show that:due to the foundation deformation effect of the lower strata,the initial break position in high-position,hard thick layers is in the middle of goaf;vertical tension fractures first occur under the middle surface,then tilt tension fractures form at both sides and a non-uniform thickness of the fracture structure forms and produces subsidence deformation;behind the coal wall tilt fractures extend and eventually complete the migration.Mining stress produces obvious changes before and after the breakage of the high,hard and thick stratum;high stress concentration forms in front of the coal wall before breakage and fracture stress concentration significantly reduces after migration.Coal seam mining under high-position,hard thick strata can easily induce dynamic phenomena.

Analysis of diffusion behavior of harmful emissions from trackless rubber-wheel diesel vehicles in underground coal mines

To define the diffusion behavior of harmful exhaust substances from diesel vehicles and support safety risk assessments of underground coal mines,we performed a multi-species coupling calculation of the emission and diffusion of harmful substances from a trackless rubber-wheel diesel vehicle.A computational fluid dynamics(CFD)model of the diffusion of harmful emissions was hence established and verified.From the perspective of risk analysis,the diffusion behavior and distribution of hazardous substances emitted by the diesel vehicle were studied under 4 different conditions;moreover,we identified areas characterized by hazardous levels of emissions.When the vehicle idled upwind in the roadway,high-risk areas formed behind and to the right of the vehicle:particularly high concentrations of pollutants were measured near the rear floor of the vehicle and within 5 m behind the vehicle.When the vehicle idled downwind,high-risk areas formed in front of it:particularly high concentrations of pollutants were measured near the floor and within 5 m from the front of the vehicle.In the above cases,the driver would not breathe highly polluted air and would be relatively safe.When the vehicle idled into the chamber,however,high-risk areas formed on both sides of the vehicle and near the upper roof.Forward entry of the vehicle caused a greater increase in the concentration of pollutants in the chamber and in the driver’s breathing zone compared with reverse entry.

Experimental and theoretical study on the dynamic effective stress of loaded gassy coal during gas release

In the process of mining coalbed methane(CBM),an unsteady state often arises due to the rapid extraction,release and pressure relief of CBM.In this case,the effective stress of coal changes dynamically,affecting the stability of the gassy coal seam.In this paper,gas release tests of gassy coal under conventional triaxial compression were performed,and the dynamic effective stress(DES)during gas release was obtained indirectly based on a constitutive equation and deformation of coal.The results show that the maximum increases in DES caused by the release of free gas and adsorbed gas under the stress of 1.1 MPa were 0.811 and 5.418 MPa,respectively,which seriously affected the stress state of the coal.During the gas release,the free gas pressure and the adsorbed gas volume were the parameters that directly affected the DES and showed a positive linear relationship with the DES with an intercept of zero.The DES of the coal sample increased exponentially with time,which was determined by the contents of free and adsorbed gas.Based on the experimental results and theoretical analysis,an effective stress model was obtained for loaded gassy coal during gas release.The results of verification indicated accuracy greater than 99%.

Effect of shear-induced contact area and aperture variations on nonlinear flow behaviors in fractal rock fractures

This study experimentally analyzes the nonlinear flow characteristics and channelization of fluid through rough-walled fractures during the shear process using a shear-flow-visualization apparatus.A series of fluid flow and visualization tests is performed on four transparent fracture specimens with various shear displacements of 1 mm,3 mm,5 mm,7 mm and 10 mm under a normal stress of 0.5 MPa.Four granite fractures with different roughnesses are selected and quantified using variogram fractal dimensions.The obtained results show that the critical Reynolds number tends to increase with increasing shear displacement but decrease with increasing roughness of fracture surface.The flow paths are more tortuous at the beginning of shear because of the wide distribution of small contact spots.As the shear displacement continues to increase,preferential flow paths are more distinctly observed due to the decrease in the number of contact spots caused by shear dilation;yet the area of single contacts in-creases.Based on the experimental results,an empirical mathematical equation is proposed to quantify the critical Reynolds number using the contact area ratio and fractal dimension.

考虑中间主应力影响的隧道开挖应力路径下大理岩应变型岩爆过程试验研究（英文）

应变型岩爆常发生于深埋隧道中,是岩爆的基本类型之一。本文利用自主研制的真三轴试验系统对大理岩试样开展隧道开挖应力路径下应变型岩爆过程试验研究。设计了两种试验路径,一种是常用的真三轴卸载岩爆试验路径,另一种是考虑隧道开挖过程中围岩中间主应力变化的新试验路径。试验过程中,应用高速摄像机记录岩样卸载临空面应变型岩爆破坏过程,并应用声发射监测系统监测岩样破坏过程中的声发射特征。试验结果表明:两种试验路径下岩样均发生了应变型岩爆破坏现象,但新试验路径下岩样应变型岩爆过程更剧烈,表明中间主应力对大理岩的岩爆行为具有显著的影响;卸载前中间主应力越大,岩样内积聚的弹性应变能越多,破坏过程中累计声发射能量越大,即岩样破坏时释放的弹性应变能越多,岩样发生岩爆破坏时弹射碎屑的总质量越大、粒度越大,破坏过程越剧烈。

加载速率对煤岩组合体试样破坏及应变能特征影响的实验与数值模拟

岩石的变形破坏过程是能量积聚与耗散的过程,岩石变形破坏是能量驱动的结果。基于室内岩石力学试验及数值模拟软件,进行了5种不同加载速率下的煤-岩组合试件的单轴压缩试验,得到了不同加载速率时煤-岩组合体的强度、变形及能量特征。试验结果表明:煤岩组合体试样的强度、变形、声发射和能量等特征均具有明显的加载速率效应,单轴抗压强度和弹性模量随着加载速率的增加呈增加趋势;峰值强度处的声发射能量呈先增大后减小再增大的趋势,而煤岩复合试样的声发射累积计数则呈先减小后增大趋势;总的吸收能量U和耗散能Ud随着加载速率的增加呈非线性增长趋势,而弹性应变能Ue则呈先增大后减小的趋势。通过选择合适的煤岩本构模型以及对煤岩组合体试样的力学参数进行准确的估算和标定,采用颗粒流程序(PFC)模拟了不同加载速率的煤岩组合体试样的单轴压缩试验,数值计算结果与室内实验结果取得了较好的一致性。该研究得到了不同加载速率下煤岩组合体的能量特征,为煤岩组合体试样的破坏提供参考。

Mountain tunnel under earthquake force:A review of possible causes of damages and restoration methods

Accurate seismic assessment and proper aseismic design of underground structures require a comprehensive understanding of seismic performance and response of underground structures under earthquake force.In order to understand the seismic behavior of tunnels during an earthquake,a wide collection of case histories has been reviewed from the available literature with respect to damage classification,to discuss the possible causes of damage,such as earthquake parameters,structural form and geological conditions.In addition,a case of Tawarayama tunnel subjected to the 2016 Kumamoto earthquake is studied.Discussion on the possible influence factors aims at improving the performancebased aseismic design of tunnels.Finally,restoration design criterion and methods are presented taking Tawarayama tunnel as an example.

大变形锚杆锚固效应及防冲吸能支护机理

大变形锚杆支护是冲击地压灾害防治的重要手段之一,为研究大变形锚杆拉伸及锚固特征,建立了大变形锚杆拉伸及拉拔数值模型,研究了拉拔力、锚杆轴力和锚固段界面剪应力演化规律,分析了结构元件设计位置对其锚固效应的影响,探讨了大变形锚杆防冲吸能支护机理。结果表明:普通锚杆在拉伸或拉拔过程中,拉拔力、锚杆轴力和锚固段界面剪应力均随着位移的增加而不断增大,但大变形锚杆进入结构变形阶段后,拉拔力、锚杆轴力和锚固段界面剪应力会处于相对稳定状态,尤其是锚固段锚杆轴力及界面剪应力分布会保持稳定;大变形锚杆的结构元件越靠近拉拔端,拉拔力波动幅度越小、自由段锚杆轴力分布越稳定、锚固段界面剪应力增速越小,更利于锚固体受力稳定。在大变形锚杆工作过程中,不仅锚杆本身应变很小和工作阻力相对稳定,而且锚杆轴力和锚固段界面剪应力分布相对稳定,当围岩发生冲击破坏时,锚杆不易被拉断或粘结界面不易破坏,可更有效地吸收围岩释放的弹性变形能,降低冲击地压灾害程度。

Study on seepage and deformation characteristics of coal microstructure by 3D reconstruction of CT images at high temperatures

To study the seepage and deformation characteristics of coal at high temperatures,coal samples from six different regions were selected and subjected to computed tomography(CT)scanning studies.In conjunction with ANSYS software,3 D reconstruction of CT images was used for the establishment of fluidsolid conjugate heat transfer model and coal thermal deformation model based on the microstructures of coal.In addition,the structure of coal was studied in 2 D and 3 D perspectives,followed by the analysis of seepage and deformation characteristics of coal at high temperatures.The results of this study indicated that porosity positively correlated with the fractal dimension,and the connectivity and seepage performances were roughly identical from 2 D and 3 D perspectives.As the porosity increased,the fractal dimension of coal samples became larger and the pore-fracture structures became more complex.As a result,the permeability of coal samples decreased.In the meantime,fluid was fully heated,generating high-temperature water at outlet.However,when the porosity was low,the outlet temperature was very high.The average deformation of coal skeleton with different pore-fracture structures at high temperatures showed a trend of initial increase and subsequent decrease with the increase of porosity and fractal dimension.The maximum deformation of coal skeleton positively correlated with connectivity but negatively correlated with the fractal dimension.

复合软岩穿层锚固效应的理论和数值模拟研究（英文）

复合软岩的锚固机理及锚固失效特征不同于单一岩体锚固。针对西部矿区复合软岩顶板锚固问题,考虑岩层间的横向剪切滑移,建立了含软弱界面复合软岩锚固的力学模型;提出采用锚固效应因子量化穿层锚杆的锚固效应;从加锚复合岩体的变形破坏过程出发,研究了系统锚杆的加固效果与机理,建立加固效果演化方程;采用有限元方法,进一步建立了复合软岩锚固的数值计算模型,分析了岩体在横向载荷作用下,节理面附近锚杆和岩体的变形特征、应力分布规律以及破坏行为。理论研究结果表明,穿层锚杆的加固效应与锚杆的刚度参数、几何参数,围岩的刚度参数和几何参数据有关。锚固效应因子是一个随着围岩工作状态改变而变化的量。从数值计算结果看,锚杆在横向荷载作用下的弯折变形主要集中在节理面附近的两塑性铰之间,变形曲线可用Doseresp模型进行表征;在2个塑性铰处,锚杆存在最大拉压应力,在节理面处,出现最大剪应力,复合岩体在节理面附近由于锚杆的反作用最先出现塑性破坏区。以上结果为进一步研究复合软岩锚固失效奠定了理论和计算基础。

Deformation tests and failure process analysis of an anchorage structure

In order to study the failure process of an anchorage structure and the evolution law of the body’s deformation field,anchor push-out tests were carried out based on digital speckle correlation methods(DSCM).The stress distribution of the anchorage interface was investigated using the particle flow numerical simulation method.The results indicate that there are three stages in the deformation and failure process of an anchorage structure:elastic bonding stage,a de-bonding stage and a failure stage.The stress distribution in the interface controls the stability of the structure.In the elastic bonding stage,the shear stress peak point of the interface is close to the loading end,and the displacement field gradually develops into a‘‘V’’shape.In the de-bonding stage,there is a shear stress plateau in the center of the anchorage section,and shear strain localization begins to form in the deformation field.In the failure stage,the bonding of the interface fails rapidly and the shear stress peak point moves to the anchorage free end.The anchorage structure moves integrally along the macro-crack.The de-bonding stage is a research focus in the deformation and failure process of an anchorage structure,and plays an important guiding role in roadway support design and prediction of the stability of the surrounding rock.

双轴压缩条件下侧向压力对不同类型岩石力学行为影响机制

大量现场案例证明,层裂结构通常出现在深部煤岩体的开挖过程中。为对探讨层裂结构形成机制提供实验数据,本论文通过测试分析四种类型岩石宏观破裂面的形成机制,研究了侧向压力对不同类型岩石力学行为的影响机制。结果表明,由于矿物成分和内部结构不同,岩石或煤的脆性和冲击倾向性均强于石膏。当侧压低于单轴强度的10%时,峰值应力和弹性模量随着侧压的增加而升高;当侧向压力高于单轴强度的10%时,峰值应力和弹性模量随着侧压的增加略有下降或保持不变。分析其原因为当侧压达到临界值时,继续施加侧压时会导致岩石局部失效。低侧压条件下,试样破坏主要受拉伸机制控制;较高侧压条件下,试样邻近自由面区域发生拉伸劈裂破坏,远离自由面区域发生剪切破坏。

Deformation transition of intact coal induced by gas injection

Gas migration in coal bed is a multiple-physical process, of which not only includes gas desorption/diffusion through coal matrix and gas Darcy flow through the cleat system, but also results in deformation of solid coal. Especially for enhanced coal bed methane(ECBM) and CO2 capture and sequestration(CCS), gas injection is mainly controlled by the gas diffusivity in the coal matrix and coal permeability.Although the relevant coal permeability models have been frequently developed, how the dual-porosity system of coal affects gas adsorption/diffusion is still poorly understood. In this paper, a series of experiments were carried out in order to investigate deformation evolution of intact coal subjected to hydrostatic pressure of different gases(including pure H2, N2 and CO2) under isotherm injection. In the testing process, the coal strain and injected gas pressure were measured simultaneously. The results show that the pressure of non-adsorptive helium remained unchanged throughout the isothermal injection process, in which the volumetric strain of the coal shrinked firstly and maintained unchanged at lower isobaric pressure. With the injected pressure increasing, the coal volume underwent a transition from shrinking to recovery(still less than initial volume of the coal). In contrast, N2 injection caused the coal to shrink firstly and then recover with decreasing gas pressure. The recovery volume was larger than the initial volume due to adsorption-induced swelling. For the case of CO2 injection, although the stronger adsorption effect could result in swelling of the solid coal, the presence of higher gas pressure appears to contribute the swelling coal to shrink. These results indicate that the evolution of coal deformation is time dependent throughout the migration of injected gas. From the mechanical characteristics of poroelastical materials, distribution of pore pressure within the coal is to vary with the gas injection,during which the pore pressure in the cleats will rapidly increase, in contrast, the pore pressure in the matrix will hysteretically elevate. Such a difference on changes of pore pressure between the cleats and the matrix will contribute to the shrinkage of the matrix as a result of initially greater effective stress.Besides, both gas-adsorption-induced swelling and decreasing effective stress also control the coal deformation transition. This work gives us an insight into investigation on influence of effective stress on coal-gas interaction.

An improved apparent permeability model considering full pore pressure range,variable intrinsic permeability and slippage coefficient

Although the slippage effect has been extensively studied,most of the previous studies focused on the impact of the slippage effect on apparent permeability within a low pore pressure range,resulting in the inability of matching the evolution of permeability in the remaining pressure range.In this paper,a new apparent permeability model that reveals the evolution of permeability under the combined action of effective stress and slippage in the full pore pressure range was proposed.In this model,both intrinsic permeability and slippage coefficient are stress dependent.Three experimental tests with pore pressure lower than 2 MPa and a test with pore pressure at about 10 MPa using cores from the same origin under constant confining stress and constant effective stress are conducted.By comparing experimental data and another apparent permeability model,we proved the fidelity of our newly developed model.Furthermore,the contribution factor of the slippage effect Rslip is used to determine the low pore pressure limit with significant slippage effect.Our results show that both narrow initial pore size and high effective stress increase the critical pore pressure.Finally,the evolutions of the slippage coefficient and the intrinsic permeability under different boundary conditions were analyzed.

基于不同预裂长度防控顶板型冲击地压风险:机理与效果研究

顶板预裂是控制潜在顶板型冲击风险的有效方法。本文采用不同预裂长度的细砂岩试样开展了三点弯曲加载试验,利用数字散斑方法(DSCM)和声发射技术(AE)对裂纹扩展全过程进行了监测,分析了预制裂隙对岩梁断裂的影响规律,揭示了岩梁断裂过程的力学机理,提出了顶板预裂设计方法,在济宁二号煤矿10303工作面进行了工程实践。研究结果表明:预裂岩梁的加载曲线表现出明显峰后特征;与完整岩梁相比,35 mm预裂岩梁的抗拉强度和最大拉应变分别降低了32.4%和33.1%,声发射b值增大了30.2%;10303工作面预裂施工后的最大微震能量和平均微震能量分别降低了25.6%和6.4%,厚层坚硬顶板预裂效果良好。

鄂尔多斯盆地侏罗系软岩底鼓控制技术:案例研究

巷道底鼓引起的围岩变形是影响中国西部煤矿安全高效生产的主要难题。为了实现对软岩巷道底鼓变形的有效控制,本文以榆树井煤矿11505工作面轨道巷为研究背景,基于极限平衡法和滑移线场理论,建立了软岩巷道底鼓模型,分析了底鼓控制机理并提出优化支护方法;采用FLAC软件模拟分析优化支护前后巷道围岩的位移场、应力场和塑性区,通过现场应用验证支护技术的可行性和适用性。结果表明:底鼓是软岩巷道围岩变形的主要形式,较合理的反底拱厚度为0.5 m,其支护效果良好;挤压破坏带和剪切破坏带分别受到拉伸破坏作用和剪切破坏作用,巷道围岩的改性和有效支护是软岩巷道底鼓控制的关键;数值模拟与理论计算得出的破坏范围基本一致,数值模拟与现场实测得到最大底鼓量分别为220 mm和240 mm,相对于原始方案分别减少55%和60%,两帮移近量明显减小。优化后的支护方案可以较好地控制巷道底鼓,对榆树井煤矿及西部矿区软岩巷道底鼓控制具有较好的工程实践意义,为软岩巷道支护设计提供有益参考。

Displacement of surrounding rock in a deep circular hole considering double moduli and strength-stiffness degradation

The problem of cavity stability widely exists in deep underground engineering and energy exploitation.First,the stress field of the surrounding rock under the uniform stress field is deduced based on a post-peak strength drop model considering the rock’s characteristics of constant modulus and double moduli.Then,the orthogonal non-associative flow rule is used to establish the displacement of the surrounding rock under constant modulus and double moduli,respectively,considering the stiffness degradation and dilatancy effects in the plastic region and assuming that the elastic strain in the plastic region satisfies the elastic constitutive relationship.Finally,the evolution of the displacement in the surrounding rock is analyzed under the effects of the double modulus characteristics,the strength drop,the stiffness degradation,and the dilatancy.The results show that the displacement solutions of the surrounding rock under constant modulus and double moduli have a unified expression.The coefficients of the expression are related to the stress field of the original rock,the elastic constant of the surrounding rock,the strength parameters,and the dilatancy angle.The strength drop,the stiffness degradation,and the dilatancy effects all have effects on the displacement.The effects can be characterized by quantitative relationships.