Wing crack propagation model under high hydraulic pressure in compressive-shear stress state

A new wing crack model subjected to hydraulic pressure and far-field stresses was proposed considering the effect of hydraulic pressure in wing crack and the connected part of the main crack on the stress intensity factor at the wing crack tip. With the equivalent crack length l _eq of the wing crack introduced, the stress intensity factor K _I at the wing crack tip was assumed to the sum of two terms: on one hand a component K _I⁽¹⁾ for a single isolated straight wing crack of length 2l, and subjected to hydraulic pressure in the wing crack and far-field stresses; on the other hand a component K _I⁽²⁾ due to the effective shear stress induced by the presence of the equivalent main crack. The lateral tensile stress and hydraulic high pressure are the key factors that induce crack propagation unsteadily. The new wing crack theoretical model proposed can supply references for the study on hydraulic fracture in fractured masses, hydraulic fracturing in rock masses.     

热破裂花岗岩渗透率变化的临界温度

利用600℃20 MN伺服控制高温高压岩体三轴试验机测量了"鲁灰"花岗岩(200 mm×400 mm)在三轴应力作用下升温过程中渗透率的变化。发现热破裂花岗岩的渗透率随温度变化存在一个临界温度Tc,即300℃。低于该临界温度时,渗透率较小,其量级为10-19m2,并且增幅较小;高于该温度后,渗透率出现了突变,且增幅较大,300~400℃,其数值增加一个量级,为10-18m2;在400℃时,渗透率的数量级增大至10-17m2。同时采用MPV-SP显微光度计定量地研究了"鲁灰"花岗岩试样20~400℃热破裂过程中裂纹数量的变化。长度大于5μm(即l5μm)和长度大于10μm(即l10μm)的微裂纹数量出现两个峰值,并且l5μm的微裂纹数量变化的峰值温度均小于l10μm的微裂纹数量变化的峰值温度;300℃后l10μm的微裂纹数量增加较快,其增加速率约1个/10℃。300℃后微裂纹的快速增加是导致热破裂花岗岩渗透率突然增加的主要原因。     

Bond interface crack propagation of fresh foundation concrete and rock under blasting load

According to concrete age, the dynamic stress intensity factors of bond interface crack of concrete-rock was calculated. Result shows that the propagation of concrete interface crack is mainly caused by tensile stress and shear stress for stress wave reflection. With the growth of concrete age, interface crack fracture toughness increases, and its capacity of resisting blasting load strengthens. Therefore, blasting vibration should be strictly controlled for fresh concrete. Supported by the National Natural Science Foundation of China(50774056, 50779050); Scientific Research Fund of Wuhan University of Science and Technology(080068, 2008XY19)     

Experimental research on combustion fluorine retention using calcium-based sorbets during coal combustion （Ⅰ）

In order to provide experimental guide to commercial use of fluorine pollution control during coal combustion, with fluorine pollution control during coal combustion in mind, this paper proposed the theory of combustion fluorine retention technology. Feasibility of fluorine retention reaction with calcium-based fluorine retention agent was analyzed through thermo-dynamic calculation during coal combustion. By simulating the restraining and retention effects and influential factors of calcium-based sorbets on vaporized fluoride during experimental combustion using fixed bed tube furnace, the paper systematically explored the influential law of such factors as combustion temperature, retention time, and added quantities of calcium-based sorbets on effects of fluorine retention. The research result shows that adding calcium-based fluorine retention agent in coal combustion has double effects of fluorine retention and sulfur retention, it lays an experimental foundation for commercial test of combustion fluorine retention. Supported by the National Natural Science Foundation of China(50476032); China Postdoctoral Science Foundation(2004035555); New Century of Talents Scheme Projects of Universities in Liaoning Province(RC-04-04)     

Experimental study on creep mechanics characteristics of gassy under disturbance conditions

Creep mechanics characteristics of large scale tectonic coal was studied under gas draingae and disturbance conditions by using the new self-developed coal gas coupling three axial creep equipment. The results show that when σ ₁ is smaller, σ ₃ is larger, gas pressure and disturbance load are smaller, gassy coal has no disturbance to creep. When σ ₃ is smaller, gas pressure and σ ₁ are larger, disturbance load is constant, gassy coal has remarkable effects of disturbance to creep. The concepts of disturbance load sensitive domain and disturbance creep sensitive domain were put forward. Under same amplitude disturbance stress condition, blasting disturbance has a stronger influence on gassy coal deformation is related to frequency of disturbance load; gas drainage, blasting excavation and mining play an important role in coal-gas outbursting. The relationship of gassy coal creep and gas pressure gradient, the creep constitutive equation built with gas pressure gradient and disturbance load as independent variables within the framework of fluid-solid two phases coupling were established. Supported by the National Natural Science Foundation (50474029); the China Natural Science Foundation(50534080); the Innovative Research Group(50221402); the Anhui University of Science &Technology Doctor’s Fund Project(11142)     

煤岩破裂过程声发射时-频信号特征与演化机制

掌握声发射信号时-频域特征及其与煤岩力学性质间的本质联系是利用该方法预测、预警煤岩失稳的基础。以具有不同夹矸和原始裂隙煤岩压缩破坏声发射监测试验为基础,引入小波变换方法,结合数字信号分析、岩石力学等相关理论深入分析煤岩破坏过程声发射时-频信号演化规律,构建了裂纹扩展释放弹性能引起应力波的振幅、频率力学表达。结果表明:受所含弱夹矸或裂隙增加影响煤岩强度、弹性模量降低,峰后软化特征明显,声发射存在由低幅振荡向高幅脉冲转化的信号激增点,强度越高,能量信号幅值显著提高、累积总能量越多,波形幅值增加,信号波形两相邻波峰间隔时间增长,夹杂的小幅振荡波越少;db5和sym2小波基函数分别与激增点、峰值点时域波形相似度最高,更适用于煤岩声发射信号研究;试验所用煤岩声发射信号主频带为0～70 kHz,煤岩强度越低信号频率分布越宽泛,随所受应力升高信号频带分布范围逐渐向主频移动。弹性模量和裂纹扩展速率共同确定了应力波振幅的变化范围,裂纹尺寸决定了振幅和频率的变化趋势,裂纹扩展速率是决定应力波频率的关键参量,进而3个参量共同影响声发射信号时-频特征。试验结果建立了裂纹表征参量与声发射信号频率、幅值的定性描述,为提高声发射信号监测准确性提供了理论基础,开展该理论的定量化应用是后续研究工作的重点。     

Experimental research on combustion fluorine retention using calcium-based sorbets during coal combustion (II)

During the fixed bed tube furnace combustion experimental study, stimulated the calcium-based sorbent grain size and microstructured influencing factors to explain the fluorine retention effect influence law, and expounded the combustion fluorine retention agent developing principle, and probed into the high-temperature fluorine retention agent technical approach. The results show that the calcium-based sorbent particle grain size and pore structure also have the bigger influence on the combustion fluorine retention effect, and reducing the calcium-based sorbent particle grain size and improving the calcium sorbent structure characteristics at very high temperature to enhance the fluorine retention effect is the important approach to the fluorine retention agent development. Supported by the National Natural Science Foundation of China(50476032); China Postdoctoral Science Foundation(2004035555); New Century of Talents Scheme Projects of Universities in Liaoning Province(RC-04-04)     

The intensity calculation of the gas absorption line by multi-line Voigt fitting

Adopted the distribution feedback type (DFB) laser to measure the coal mine gas methane, according to the methane located 1.6 μm nearby 2ν 3 with a R9 direct absorption spectrum, attraction wire intensity of each line was calculated through the multi-line Voigt fitting. The experimental result indicates that in the obtained four attraction recover of wire, the maximum deviation is 2.7%, and the minimum deviation is 0.02%, other results are all in experimental error scope. This research method may apply in the spectrum survey methane gas density, it has characteristics including high precision, strong selectivity, fast response and so on. Supported by the National Natural Science Foundation of China (50574005); Natural Science Foundation of Education Department of Anhui, China (2005KJ081)     

A triaxial creep model for coal containing gas and its stability analysis

Triaxial creep tests on CCG specimens were systematically performed using a self-made creep seepage experimental apparatus for determining the creep law of CCG. An improved triaxial creep model of CCG was established on the basis of a Nishihara model and another visco-elasto-plastic model, parameters of which were fitted on test data. Furthermore, the creep model is validated according to the result of triaxial creep experiments, and the outcome shows that the proposed triaxial creep model can properly characterize the properties of various creep deformation phases of CCG, especially the accelerating creep phase. At the same time, the instability conditions of CCG were presented based on the discussion of the improved model’s stability in terms of stability theories of differential equation solution. Supported by the National Natural Science Foundation of China(50874124); the National Basic Research Program of China (973) (2005CB221502); the National Natural Science Foundation of China(50534080); the Natural Science Foundation Project of CQ CSTC(2008BA6028)     

Experimental investigation of divergence of confined turbulent jets

Conclusions The author gives the results of experimental investigations of confined turbulent flows between two parallel surfaces with sudden broadening of the cross section of the channel followed by narrowing. They find that the angle of divergence of the jet does not depend on the initial speed of the incoming current to the chamber, u_ic, or the length of the inlet channell _ic and is equal to about 20° as long as the formation of the main jet is not subjected to the confining effect of the side walls, i.e., up to m≤0.3. If the jet cross section is m>0.33 and the inlet and outlet channels are symmetrical relative to the width of the chamber and on the same axis, there is “adhesion” of the jet to one of the side walls on account of the pressure redistribution. The length of the circulation zone depends linearly on the jet confinement parameter B_r/2d₀, andl _R is constant for Reynolds numbers between 0.5·10⁴ and 1.6·10⁴. The results of the above investigations can be used to construct schemes of formation of currents in large-span extraction workings and analysis of their ventilation. Mining Institute, Kola Branch, Academy of Sciences of the USSR, Apatity. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 3, pp. 106–111, May–June, 1981.     

法向应力对岩石剪切裂纹演化与贯通机理的影响

利用自主研发的煤岩剪切细观试验装置,以砂岩为研究对象,开展了不同法向应力条件下的岩石剪切细观开裂演化与贯通机理试验研究,分析了砂岩剪切细观开裂演化过程及细观贯通机理,探讨了法向应力对细观开裂和细观裂纹形态特征的影响。研究结果表明:随着法向应力的增加,峰后残余强度呈增加趋势,试件表面起裂裂纹的长度在减小,施加法向应力后裂纹开裂时间均发生在峰前阶段;中部裂纹形成和贯通过程中出现的岩桥,在摩擦滑移的过程中发生不断的偏转,导致脱落,形成局部剥离;端部贯通裂纹形成后,由于法向应力的限制及端部应力集中,出现端部次级裂纹,并与原有的贯通裂纹连通,形成分叉,引起端部局部剥离;法向应力的作用,使得贯通裂纹周边颗粒间产生许多微裂纹,加剧了剪切裂纹左右侧壁的损伤范围;随着法向应力的增大,砂岩剪切过程中出现的宏观间断裂纹的数目呈逐渐增加规律,间断裂纹的长度呈减小趋势,次级裂纹数目和裂纹发育带范围均呈增加趋势。     

On the treatment of thermal cracks in lining concrete of water conveyance system of Three Gorges Project permanent ship locks

A comprehensive investigation was performed for repairing the different types of cracks appearing on the surface or inside the concrete lining at various depths. The material properties used in grouting and two methods for crack repair were discussed in details, and consequently reliable repair measures were proposed and implemented. It is a better choice to adopt the hole-drilling method for the relatively regular crack. The grouting pressure should not be too high and it is generally between 0.4∼0.6 MPa. For the second time grouting, the pressure maybe increased to 0.8 MPa. Other method is the pasting nozzles method which is more suitable for irregular cracks such as cracks with intensive density and crossing cracks. Its grouting pressure is generally between 0.6∼1.0 MPa. The in-situ tests in Three Gorges Project demonstrate favorably the feasibility and applicability of the proposed methods for crack repair within the lining concrete. Supported by the National Natural Science Foundation of China (10602049)     

基于裂纹扩展模型的深部硐室围岩致裂规律

根据岩体的非均匀性和存在初始裂纹的特征,在二维有限差分程序中建立了非均质体二维模型,并在模型中考虑初始裂纹的影响,利用程序中的自带编译语言,实现了服从不同分布的初始裂纹的长度和角度的赋值。在模型中,利用亚临界裂纹扩展理论描述与时间相关的裂纹亚临界扩展过程,计算过程可体现裂纹扩展的时间效应,从而实现对所模拟结构的寿命预测。模型中裂纹的扩展方式假定为形成翼型裂纹的形式,利用翼型裂纹的简化模型对裂纹的扩展尺寸,应力强度因子等参数进行计算。在每一计算步中,每个单元中的裂纹扩展方向与该时刻单元所受应力情况相关,应力强度因子与该单元所受应力大小及翼型裂纹简化长度相关。利用该模型对高地应力条件下孔洞开挖卸荷导致围岩破坏的过程进行模拟,分析了深部岩体开挖导致的围岩破坏规律,对不同的孔洞形状和初始裂纹的分布情况分别进行了分析,计算结果显示了非连续破裂的形成与初始裂纹角度分布的关系:分区破裂的表现形态与初始裂纹和最大压应力的夹角相关,并且不同初始裂纹角度均值也会导致围岩破裂时间不同。通过建立的多种孔洞形状开挖模型,对不同孔洞形状围岩破裂形态及破坏时间的规律进行总结,发现相同计算步数内方形孔洞周边围岩处破坏单元数量最多,圆形孔洞周边围岩破坏单元数量最少。研究结果证实了裂纹的分布对孔洞周边围岩破坏形态的影响,对裂纹扩展的时间效应的分析可实现对围岩破坏程度和范围的预测,可为深部高地应力条件下诱导致裂非爆连续开采的实施时间和方式提供指导。     

Bifurcation characteristics of coal spontaneous combustion and analysis of critical state of gaseous reaction in a packed bed

The numerical model was presented for the coal combustion in the packed bed. The bifurcation characteristic of the ignition-extinction of solid-phase smoldering and transition to flaming was studied for the packed bed of coal. One of the Frank-Kamenetskii parameter β ₁ was selected as the control parameter. The computed results show that the bifurcation curve is obviously divided into two zones of solid-phase reaction and gasphase reaction, and the total process of ignition-extinction presents twice bifurcation characteristic. Moreover, the vanishing of critical state of ignition-extinction is studied. One of the transition points, ɛ ₂=0.05, is numerically solved for the vanishing of critical state. The larger the value of ɛ ₂ is, the easier the gas-phase can react. However, the combustion temperature will decrease with increasing ɛ ₂. The other transition point α ₂=0.53 is also obtained. With increasing the value of α ₂, the combustion temperature of gas-phase reaction is close to the smoldering temperature of coal. When α ₂ is infinite, the only reaction occurring is the smoldering combustion of solid-phase, and the gas-phase cannot react. Supported by the National Natural Science Foundation(50574049); National Key Technology R&D Pogram of China(2006BAK03B05)     

Biological liquefaction characteristics of Jurassic weak ＆ non-stick coal in Hengshan, North Shaanxi Province

Jurassic weak & non-stick coal in Hengshan of North Shaanxi Province was pretreated by the nitric acid. Then, it was biodegraded by Phanerochaete chrysosporium. The biodegradation role of the white-rot fungus for coal is extremely significant. Orthogonal test demonstrate that liquefied time, liquefaction temperature and the amount of fungus liquids etc. are the main factors affecting the coal biodegradation rate. The best technical condition of the coal biological liquefaction was got. Comparing the coal sample before biodegradation with that after biodegradation, it is found that the ash of the coal residue after biodegradation reduces significantly, H and O contents increase, C and N contents decrease. The biodegradation change the coal macromolecular structure. Supported by the National Natural Science Foundation of China (40772103)     

Carbon monoxide adsorptive capability of low rank coal’s maceral

The centrifugal separation with gravity experiment was made for getting every pure macerals like inertinite and vitrinite, and the isothermal adsorption tests of pure maceral are carried out at 30, 40, 50, 55, 60, 65 °C, respectively, after analyzing the proximate, element and maceral of coal samples, which was aimed to study the CO adsorptive capability of every maceral of low rank coal at difference temperature and pressure. The results show that the adsorption isotherm of CO can be described by Langmuir equation because it belongs to the Type I adsorption isotherm at low temperature(T⩽50 °C), and the temperature effect on coal adsorption is greater than of pressure in lower temperature and pressure area; what’s more, the relationship is linear between the coal adsorption quantity of CO and the pressure at high temperature(T>50 °C), it can be described by Henry equation(Q=KP), which increases with pressure. Both temperature and pressure has great influence on CO adsorptive capability of low rank coals, especially the temperature’s effect is so very complex that the mechanism need to study further. At the same time, the volatile matter, inertinite, oxygen-function groups and negative functional groups are high popularly in low rank coal samples, especially, the content of hydroxide(-OH) has great influence on CO adsorption in that the inertinite has stronger effect than vitrinite on adsorptive capability of low rank coal samples, the result is same to the research on CH₄ adsorption. Supported by the National Natural Science Foundation of China (50474080); Educational Department Foundation for Returnee     

冲击倾向性煤体的三点弯曲动态断裂实验

采用三点弯曲冲击断裂实验装置和分布式多火花高速摄影系统对冲击倾向性煤体内裂纹扩展过程进行了观测，分析了裂纹扩展速度、动态裂纹扩展摸式和裂纹扩展的非稳定性.研究发现：冲击倾向性煤体内裂纹扩展具有高度的非线性特征；煤体的非均质性和不连续性对动态裂纹扩展模式和裂纹扩展速度有较大影响.实验结果解释了由放炮等震动诱发冲击地压灾害的滞后突发机理.     

Geophysical criterion of pre-outburst crack propagation in coal beds

The process of crack propagation in the coal face area is considered as an informative sign of coal and gas outburst hazard. In the known condition of crack growth at a certain distance from a coal face, it is suggested to replace mechanical parameters by geophysical data through application of different evaluation approaches: actual stresses—by spectral–acoustic method relative to amplitudes of highfrequency and low-frequency components of acoustic signal generated by mining machines in coal face area; pore pressure—by analysis of methane concentration in mine air in coal face area; strength of the most folded coal bed—by measuring strength based on penetration depth of a steel cone. The author analyzes the influence of acoustic, strength and permeability and porosity properties of coal face area on limit value of geophysical pre-outburst crack propagation criterion.     

Research on inversion high mining pressure distribution and technology of preventing dynamic disasters by MS monitoring in longwall face

Under two rock strata combination conditions, over 10,000 microseismic events were received with microseismic location monitoring technology which possessed by the author’s studying team, used in fully mechanized coal face of Huafeng Mine of Xinwen Coal Mining Group Co., Shandong Province. On the basis of the achievement of the location results, the conclusions were drawn as follows: On the basis of the achievement of 3D strata fracturing situation and the section plane of microseimic events in different areas, the relationship between spatial structure of overlying strata and mining pressure field was found, and we might describe distribution range of dynamic pressure of advance pressure and lateral stress around long face, and range of structure ad-tivation. Quantitative guidance to prevent dynamic disasters was provided. The practice in coal mine got a effective results. According to the FLAC^3D soft numerical simulation of diameter drilling hole (the diameter is 300 mm) to relieve pressure in specified geological condition in Huafeng Mine, the right distance of two dirlls is 2.5 m and the right depth is 12 m. The research pro-vided basic guiding and practical experiences for the underground microseismic monitoring and disaster prevention in side slopes or tunnels engineering. Supported by the National Natural Science Foundation of China (40674017, 50534080); the Open Fund of State Key Laboratory of Coal Resources and Safe Mining(2007-04); the Open Doctor Innovation Fund of Shandong Province (200703020); the Chinese Postdoctoral Science Fundation (20080440304)     

A t10-based method for evaluation of ore pre-weakening and energy reduction

Currently the effect of the pre-weakening of ore particles by high voltage pulses is evaluated by the percentage change of A 1 b values between pulse-treated and untreated ore particles. The values of A 1 b, widely used as an ore breakage competence indicator in the mineral industry, are determined from the parameters of the JKMRC breakage models. In this study a t₁₀-based method was developed to predict the degree of size reduction, t₁₀, of pulse-treated particles from that of untreated particles broken at the same size/energy level. This method incorporates one parameter, C_Ab, which is equivalent to the percentage change of A 1 b values.The t₁₀-based method was validated using nine sets of comparative JK Rotary Breakage Tester data on pulse-treated and untreated ore samples over a wide range of impact specific energies and particle sizes. The t₁₀-based method can be used to calculate the energy reduction due to the pre-weakening effect in the downstream comminution process. It indicates that the energy reduction by pre-weakening increases with an increase in the target product fineness and the degree of pre-weakening, and with the decrease in feed particle size.