煤层上覆岩层力学性质随赋存深度变化试验

为获得煤层上覆岩层力学性质随赋存深度变化的规律,钻孔选取从地表到煤层的所有完整岩石,通过室内力学试验获取相应力学参数.试验结果表明:试样的天然密度、抗拉强度、单轴抗压强度和弹性模量等随着赋存深度增加而增大,吸水率、泊松比随着赋存深度增加而减小;试样力学性质除了与赋存深度有关外,还与岩性有直接关系;试验数据的离散性随着赋存深度增加而增大.造成试验数据离散性的原因除构造应力、煤层采动及温度影响外,主要是砂岩等沉积岩试样内部颗粒随着应力解除而重新耦合.     

利用XRD分析高温下淮南煤灰矿物质变化

利用X射线衍射分析四种淮南煤在不同温度下煤灰矿物组成变化。结果表明：淮南煤中主要晶体矿物有高岭石、石英、方解石、黄铁矿等,高岭石类矿物含量越高,煤灰熔点越高;方解石和黄铁矿含量越高,煤灰熔点越低。煤灰中主要晶体矿物有石英、硬石膏、赤铁矿等,硬石膏和赤铁矿含量越大煤灰熔点越低。随着温度的升高,煤灰中石英、硬石膏、赤铁矿等结晶矿物含量逐渐减少,生成新的矿物质,莫来石的生成是导致淮南煤灰熔点高的主要原因,钙长石起到降低煤灰灰熔点的作用。     

Temperature influence on macro-mechanics parameter of intact coal sample containing original gas from Baijiao Coal Mine in China

Investigation of temperature effect on mechanical parameters of coal is very important for understanding the mechanical response of coal bed at high temperature. It is especially beneficial for mitigating the thermal-induced disasters occurred in those coal mines suffering from heat hazard. In this work, coal samples, obtained from the No. 2442 working face of Baijiao Coal Mine, were subjected to uniaxial compression ranging from 20 to 40 °C with an interval of 5 °C. The apparatus used was designed to obtain deformation of a stressed sample, as well as the emission of gases desorbing from coal matrix. The adsorbed gas desorption caused by heating is measured during the entire testing. It is evident that the concentrations of releasing gas (containing methane, carbon dioxide and ethane) slightly rise with increasing temperature. Gas movement observed is closely related to the deformation of coal sample. Both uniaxial compressive strength and elastic modulus of coal samples tend to reduce with temperature. It reveals that increasing temperature can not only result in thermal expansion of coal, but also lead to desorption of preexisting gas in coal which can in turns harden coal due to shrinks of the coal matrix. Even though desorption of adsorbed gas can contribute to the hardening effect for the heated coal, by comparison to the results, it could be inferred that the softening of coal resulted from thermal expansion still predominates changes in mechanical characters of coal sample with temperature at the range from 20 to 40 °C.     

Experimental research on coal seam similar material proportion and its application

In this paper, the optimization design of the low strength mechanical test and orthogonal test have been analyzed in order to simulate the mechanical properties of thick and extra-thick coal seam accurately in a similar material simulation test. The results show that the specimen can reach a wider range of strength when cement has been used compared to that of gypsum, suggesting that cement is more suitable for making coal seam in similar material simulation tests. The uniaxial compressive strength is more sensitive to cement than coal or sand. The proportion of coal and sand do not play a decisive role in uniaxial compressive strength. The uniaxial compressive strength and specimen density decrease as the mass percent of coal and aggregate–binder ratio rise. There is a positive correlation between uniaxial compressive strength and density. The No. 5 proportion(cement: sand: water: activated carbon: coal = 6:6:7:1.1:79.9)was chosen to be used in the similar material simulation test of steeply dipping and extra-thick coal seam with a density of 0.913 g/cm~3 and an uniaxial compressive strength of 0.076 MPa which are in accordance with the similarity theory. The phenomenon of overburden stratum movement, fracture development and floor pressure relief were obtained during the similar material simulation test by using the proportion.     

弱还原气氛下淮南煤灰矿物质特性研究

对淮南煤在弱还原气氛下的矿物质特性进行实验研究,用X-射线衍射和红外光谱分析不同温度下煤灰矿物组成变化。结果表明：淮南煤中主要晶体矿物有高岭石、石英、方解石、黄铁矿等,高岭石类矿物含量越高,煤灰熔点越高;方解石和黄铁矿含量越高,煤灰熔点越低。煤灰中主要晶体矿物有石英、硬石膏、赤铁矿等,硬石膏和赤铁矿含量越高煤灰熔点越低。随着温度的升高,煤灰中石英、硬石膏、赤铁矿等结晶矿物含量逐渐减少,生成新的矿物质,莫来石的生成是导致淮南煤灰熔点高的主要原因,钙长石起到降低灰熔点的作用。     

Compressive strength of polymer grouting material at different temperatures

In order to study the influence of temperature on compressive strength of polymer grouting material, the compression specimen injection mold is self-made, and the uniaxial compressive test was carried out in the temperature control box under different temperatures. The change regularity of compressive strength of polymer grouting material under different temperatures and the law of volume changes of polymer samples were obtained. The experimental results show that: the compressive strength of polymer material increases with the increase of density; the temperature change has a certain influence on the compressive strength of polymer grouting material; the compressive strength decreases with temperature increases under the same density, but the compressive strength is not significantly affected by temperature when the density is less than 0.4 g/cm³; the volume change of the samples accords with the law of thermal expansion and contraction when temperature changes, and the increase of the volume is obvious when it is under high temperature. The achievements will provide an important basis to the application of the polymer grouting material.     

Mechanical behavior of coal under different mining rates: A case study from laboratory experiments to field testing

During deep mining, the excavation disturbance stress path is the domination factor for the stability of the surrounding rock mass as well as the ground pressure. One of the important parameters of the stress path is the loading or unloading rate of the disturbed rock or coal, which depended on the mining rate. To achieve a well understanding of the mining rate and its effect on the coal behavior, a preliminary case investigation of the mechanical properties of the coal at the various mining rates in both the laboratory scale and field scale was performed. Based on the uniaxial compression test and the digital image correlation(DIC) method, the mechanical behavior of the coal samples, such as the evolution of the strength,surface deformation, crack propagation, and elastic strain energy of the coal under the various loading rates were analyzed. A threshold range of the loading rate has been observed. The uniaxial compressive strength(UCS) and releasable elastic strain energy(Ue) increase with increasing loading rate when the loading rate is below the threshold. Otherwise, the UCS and Uemay decrease with the loading rate.Under the low loading rate( 0.05 mm/min), the tensile deformation of the original defects could result in crack coalescence, whereas failure of the coal matrix is the key contributor to the crack coalescence under the high loading rate(greater than 0.05 mm/min). Afterwards, with the consideration of the bearing capacity(UCS) and energy release of the mining-disturbed coal mass(Ue), a power exponential relationship between the mining rate(MR) in the field and the critical loading rate(vc) in the laboratory was proposed. The application potential of the formulas was then validated against the field monitored data.Finally, based on the critical loading rate, the released strain energy, and the monitored pressure on the roof supports, a reasonable mining rate MRfor the Ji 15-31030 working face was determined to be approximately 3 m/d.     

Resistivity response to the porosity and permeability of low rank coal

Laojunmiao coal samples from the eastern Junggar basin were studied to understand the relationship between coal resistivity and the physical parameters of coal reservoirs under high temperatures and pressures.Specifically,we analysed the relationship of coal resistivity to porosity and permeability via heating and pressurization experiments.The results indicated that coal resistivity decreases exponentially with increasing pressure.Increasing the temperature decreases the resistivity.The sensitivity of coal resistivity to the confining pressure is worse when the temperature is higher.The resistivity of dry coal samples was linearly related to φ~m.Increasing the temperature decreased the cementation exponent(m).Increasing the confining pressure exponentially decreases the porosity.Decreasing the pressure increases the resistivity and porosity for a constant temperature.Increasing the temperature yields a quadratic relationship between the resistivity and permeability for a constant confining pressure.Based on the Archie formula,we obtained the coupling relationship between coal resistivity and permeability for Laojunmiao coal samples at different temperatures and confining pressures.     

Simulation of microwave's heating effect on coal seam permeability enhancement

As hydraulic fracturing was forbidden in some countries due to possible negative environmental impacts and enhanced coalbed methane(ECBM) was restricted by in-situ conditions, microwave heating was proposed to enhance coalbed permeability. One of the mechanisms of improving coal permeability with microwave irradiation is that thermal expansion caused by microwave heating. To study the influence of microwave's heating effect of coal samples, the simulations were conducted using a coupled electromagnetic, thermal and mechanical model in this paper. The temperature, Von-Mises stress and strain distribution of coal sample are recorded every 10 s. The permeability distribution is also obtained based on the relationship between strain and permeability from articles. It was found that volume average temperature, stress, strain and permeability increase almost linearly with time. The average permeability increased from 1.65×10~(-16) m~2 to 3.63×10~(-16)m~2 under 2.45 GHz and 500W microwave radiation after 300s. The significant increase proved microwave to be effective in coal seam permeability enhancement.     

大尺度冲击性煤体电阻率变化规律的实验研究

在未加载条件下对大尺度煤样的电阻率测试结果表明,在自然状态下煤样的电阻率较大;经过浸泡后其电阻率明显下降．在单轴压缩条件下的大尺度冲击性煤样电阻率实验表明,电阻率变化曲线整体上成不对称的“凹”型,基本符合二次曲线;煤样电阻率随压力增加逐渐减少,当达到一定的应力值时,电阻率达到最小值;继续加载,电阻率将升高,直到完全失稳．1#、3#和4#煤样单轴抗压强度与其受载过程中的视电阻率变化存在一定的正相关性;受载煤体的电阻率变化与其变形破裂过程中的裂隙分叉、发育、汇合贯通密不可分;兼有剪裂和拉裂特点的破坏类型可能是大尺度煤样较常见的破坏形式．     

煤及半焦的XRD结构分析

通过XRD(X射线衍射)对3种单煤以及不同温度半焦的结构进行分析:晋城无烟煤与潞安贫煤在873~1073 K之间温度的半焦性能比较好,而烟煤则在873 K温度左右的半焦性能良好。样品微晶参数的测试结果表明,随着热解温度升高与焦化程度的增加,"煤晶核"BSU的延展度、网面间距、微晶中芳香层单层之间的距离d002、芳香层片平均堆砌厚度Lc、芳香层片的直径La呈现规律性变化。随着热解温度的不断增加,002衍射峰的峰位偏移程度不大,煤的芳香层单层之间的距离d002变化不明显,表示芳香层叠片大小的Lc、La值具有随着加热温度的升高呈先减小后增大的趋势,但是煤热解的三个阶段性特征比较明显。原因是第一阶段随热解温度的升高,碳、氢元素的含量呈先降低后升高;第二阶段芳香族化合物增加与挥发物质的大量逸出;最后阶段中脂肪族化合物、脂环族化合物裂解同时侧链减少,导致煤中大部分物质聚合成稠和度更大的芳环结构,结构渐趋有序化,晶化程度增加。     

Physical and mechanical properties of sandstone containing a single fissure after exposure to high temperatures

In order to investigate the physical and mechanical properties of sandstone containing fissures after exposure to high temperatures,fissures with different angles α were prefabricated in the plate sandstone samples,and the processed samples were then heated at 5 different temperatures.Indoor uniaxial compression was conducted to analyze the change rules of physical properties of sandstone after exposure to high temperature,and the deformation,strength and failure characteristics of sandstone containing fissures.The results show that,with increasing temperature,the volume of sandstone increases gradually while the quality and density decrease gradually,and the color of sandstone remains basically unchanged while the brightness increases markedly when the temperature is higher than 585 ℃;the peak strength of sandstone containing fissures first decreases then increases when the temperature is between 25℃and 400℃.The peak strain of sandstone containing fissures increases gradually while the average modulus decreases gradually with increasing temperature,and the mechanical properties of sandstone show obvious deterioration after 400 ℃.The peak strain of sandstone containing fissures increases gradually while the average modulus decreases gradually with increasing temperature;with increasing angle αof the fissure,the evolution characteristics of the macro-mechanical parameters of sandstone are closely related to the their own mechanical properties.When the temperature is 800 ℃,the correlation between the peak strength and average modulus of sandstone and the angle α of the fissure is obviously weakened.The failure modes of sandstone containing fissures after high temperature exposure are of three different kinds including:tensile crack failure,tensile and shear cracks mixed failure,and shear crack failure.Tensile and shear crack mixed failure occur mainly at low temperatures and small angles;tensile crack failure occurs at high temperatures and large angles.     

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.     

大掺量矿物细粉掺和料活性粉末混凝土高温性能

研究了大掺量矿物细粉活性粉末混凝土高温爆裂性能和高温后的抗压强度.结果表明,试件的爆裂温度随着水胶比的减小而降低,爆裂几率随水胶比的降低而增大;高温爆裂的初始时间和温度随矿物细粉掺和料掺量增多而降低;聚丙烯纤维能有效地改善活性粉末混凝土抗爆裂性能;活性粉末混凝土经200℃高温后的抗压强度有所增加,且聚丙烯纤维的加入可使活性粉末混凝土抗压强度和200℃范围内残余强度率有一定幅度提高.     

Flexibility of a 300 MW Arch Firing Boiler Burning Low Quality Coals

Experimental investigations on the flexibility of a 300 MW Arch Firing (AF) coal-fired boiler when burning low quality coals is reported.Measurements of gas temperature and species concentration and char sampling using a water-cooled suction pyrometer were carried out along the furnace elevation.The carbon content and the size distributions of the char samples were obtained.The char morphology was examined using a field emission scanning electron microscope (FESEM).The char sampling was performed on this type of boiler for the first time.The results indicate that the flexibility of this boiler burning low quality coals under a moderate boiler load is better than its flexibility under a high boiler load.Because of the insufficient capacity of the coal pulverizers used, in case of low coal quality the pulverized coal fineness will drastically decrease under high boiler loads.This causes an increase in the loss due to incomplete mechanical and chemical combustion.This is the main cause of a low burnout degree of the pulverized coal and the decrease of the flexibility of this AF boiler under a high boiler load.     

Law of gas production during coal heating oxidation

Coal spontaneous combustion is a great threat to mine safety, and gas is the key index to describe coal spontaneous combustion. Taking the coal samples of different kinds of coal as research object, the temperature programmed oxidation experiment was carried out, and the gases produced by coal samples at different temperatures were collected and analyzed by gas chromatography. This research studied the variation characteristics of gas species and gas concentrations in different coal samples during heating oxidation. The experimental results show that different coal samples produce different kinds of gases in the process of heating and oxidation. The order of gas production is CO, C_2H_6, C_2H_4, C_3H_8, and the relationship between gas production and temperature is approximately exponential. With the increase of coal metamorphic degree, the turning point temperature of sharp rise in coal sample gas production rate become higher, the oxidation ability of coal sample decreases, and the quantity of gas production decreases during the same time period.     

Settlement behavior of coal mine waste in different surrounding rock conditions

In order to investigate the influence of complex conditions of in-situ surrounding rocks on the settlement behavior of nubbly coal mine waste subjected to high gravity pressure,four kinds of loading chambers made of different similar materials with different elastic moduli in experiments were used to simulate the deformation features of in-site rocks,including soft,moderate hardness,hard and extra-hard rocks. The results show that all the settlement-axial load （or axial strain-stress） curves obtained under four different surrounding rock conditions present power-exponential function feature. The final settlement of coal mine waste under the same axial load is closely related to the lumpiness gradations and the deformation behavior of chamber materials used to simulate behaviors of different in-situ surrounding rocks. In the same surrounding rock condition,the final settlement under the same maximum axial load decreases with the decrease of the proportion of larger gradation of coal mine waste. While for the same lumpiness gradation case,the settlement increases with the decrease of elastic modulus of simulated surrounding rocks and the lateral pressure induced by axial load increases with the increase of elastic modulus of loading chambers that are used to simulate different surrounding rocks. The test results also reveal that both the compaction curve and lateral pressure curve show a three-stage behavior,and the duration of each stage,which is closely related to gradations and the deformation feature of loading chamber materials,decreases with the increase of the proportion of the small size of coal mine waste and elastic modulus of the simulated rock materials.     

微波辐射下含水率对混凝土力学性能影响

微波辅助混凝土骨料回收是一项污染少、能耗低的新型绿色技术,是近年来国内外研究的热点方向。为探究微波辐射条件下含水率变化对混凝土加热效果及强度弱化的影响规律,分析微波加热完成后混凝土内部骨料与砂浆的分离效果,采用不同加热路径对混凝土试块进行加热,获得试块的升温特性,并利用单轴压缩实验得到不同含水率试块加热完成后的抗压强度。试验表明,微波辐射功率和含水率是影响混凝土破碎的两个重要因素,试块在含水率相对较高时,采用高功率微波连续加热混凝土,试块在短时低温下就会爆裂,骨料与砂浆分离界面明显,可以从破碎后的混凝土中剔选出来较多砂浆附着率低的完整骨料。文章通过探讨微波辐射下含水率对混凝土强度弱化的影响规律,为微波辅助混凝土再生技术的进一步发展提供参考与借鉴。     

灰岩单轴抗压特性的浸水效应研究

为了考察软岩浸水后软化行为对单轴抗压特性的影响,取河南陈四楼煤矿二1煤底板太原组灰岩为试验材料,在三种不同的加载速率下,对不同浸水时间下试样进行单轴压缩试验,得到关于灰岩抗压特性的浸水效应。试验结果表明:在一定的加载速率下,随浸水时间增加,抗压强度和弹性模量逐渐减小,且降低幅度越来越小;随浸水时间增加,试样逐渐由弹性变形转变为塑性变形,但极限应变基本不变;试样内部不可逆的损伤破坏加剧,总应变能和弹性能与浸水时间呈指数关系,耗散能随浸水时间的变化可以用线性关系拟合。     

水-温循环作用下千枚岩的动态拉伸特性

为研究水-温耦合作用下0°层理倾角千枚岩的动态拉伸特性变化规律,分别对3组试样进行0、1、3、5、7、8、11次温度循环自然降温、温度循环冷水降温、干湿循环后,采用霍普金森杆试验装置对0°层理倾角千枚岩试样开展动态巴西劈裂试验,从动态拉伸应变曲线、动态峰值抗拉强度、动态弹性模量、能量分析与宏观破坏5个角度研究水、温劣化条件下千枚岩的动态拉伸特性。结果表明：千枚岩应力应变曲线包括极速弹性变形阶段、屈服变形阶段、破坏变形阶段;随着水-温循环次数的增加,千枚岩应力-应变曲线极速弹性变形阶段逐渐缩短,屈服变形阶段的应变增长率不断增大;千枚岩动态峰值抗拉强度呈负指数函数关系变化,耗散能比不断减小;水-温耦合条件下,千枚岩峰值抗拉强度、耗散能比普遍小于温度循环自然降温时;动态冲击下,千枚岩发生贯穿层理的张拉破坏,主要破碎为2块;随着水-温循环次数的增加,千枚岩主碎块发生沿层理面的张拉与穿层理面的剪切复合破坏,千枚岩碎块的平均尺寸不断减小;温度循环冷水降温条件下,千枚岩碎块的平均尺寸更小,且降幅最为显著。