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.

Similarity criteria and coal-like material in coal and gas outburst physical simulation

Coal and gas outburst is one of the main gas hazards in coal mines. However, due to the risks of the coal and gas outburst, the field test is difficult to complete. Therefore, an effective approach to studying the mechanism and development of outburst is to conduct the similar physical simulation. However, the similarity criteria and similar materials in outburst are the key factors which restrict the development of physical simulation. To solve those problems, this paper has established similarity criteria base on mechanics model, solid-fluid coupling model and energy model, and presented high similar materials. Combining with three groups of similar number, and considering similar mechanical parameters and deformation and failure regularity, the similarity criteria of outburst is determined on the basis of the energy model. According to those criteria, we put forward a similar material consists of pulverized coal, cement, sand, activated carbon, and water. The similar material has high compressive strength and the accordant characteristics with the raw coal, include density, porosity, adsorption, desorption. The new research is promising for preventing and controlling gas hazards in the future.

Similar material simulation of time series system for induced caving of roof in continuous mining under backfill

With the help of similar material simulation test,time series system for induced caving of roof in continuous mining under complex backfill in ore body No.92 of Tongkeng Tin Mine was studied. According to the similarity theory,a two-dimensional similar simulation test-bed was constructed. The stress and displacement that change along with the advance of mining were acquired and analyzed automatically by data system. The processes of continuous mining of ore-block in 5 intervals and artificial induced caving of roof were simulated. The results of the test show that ore body remained as safety roof in thickness of 15 m guarantees the safe advance of stoping work face. Caving of safety roof puts in practice at the first two mining intervals when the third interval of continuous mining is finished,and one interval as the safety distance should be kept all the time between stopping and caving. While mining in the last interval,pre-slotting should be implemented first of all,and the roof of the last two mining intervals is caved simultaneously. Only this kind of time series system can be an efficient and safe way for induced caving of roof in continuous mining.

Damage and failure characteristics of rock similar materials with pre-existing cracks

In order to further study the damage and failure mechanism for rock similar materials,this study investigated the mechanical properties and failure characteristics,law of damage space development,and damage evolution characteristics for rock similar materials with pre-existing cracks of varying length under uniaxial compression load.The equipment used in this study is the self-developed YYW-Ⅱ strain controlled unconfined compression apparatus and the PCIE-8 acoustic emission monitoring system.Results show that,as the length of pre-existing crack increases:(1) the peak and residual strength reduces,and the peak axial strain and the strain during the initial compression phase increases;(2) the major failure mode is changed from shear failure to tensile failure along a vertical plane that passes the middle of the pre-existing crack;(3) The damage increases during the stable and accelerated development stage,and the effect of the pre-existing cracks is more during the accelerated development stage than the stable development stage.

Study on relation between tectonic stress and coal-mining subsidence with similar material simulation

Using a minitype and stress-type test device for similar material simulation of coal-mining subsidence, the relation between tectonic stress and coal-mining subsidence was successfully simulated, furthermore, the test period of similar material simulation was obviously shortened and the test process was more dexterous and convenient. To do simi-lar material simulation with the minitype and stress-type test device was feasible and high-efficient. Bringing two models with the same geological and mining conditions to bear lateral compressive stress and tensile stress respectively and simulating the process of underground mining, the test results indicate that: under the compressive stress, the col-lapse of the coal roof occurs belatedly and the damaged range in cover of coal seam is smaller, therefore the movement and deformation of the cover and its damage to the ground geological environment are not evident; whereas under tensile stress, the situation is contrary to which mentioned above. A conclusion was obtained from the test that the ground environment hazards in coal mining areas were controlled by the regional geo-logical tectonic stress field.

Application of ultrasonic in strength measurement of similar materials of limestone

Similar materials such as cement, gypsum and sand are options for simulating limestone characteristic.A series of reasonable proportions are chosen to do similar experiments of Karst roof based on the proportions testing of small samples indoors. Applying on ultrasonic, the velocities of transverse wave and vertical wave of similar samples have been inspected with the sound wave instrument. Dynamic modulus of elasticity and Poisson's ratio of the samples have been educed. According to the testing data, the relationship between the transverse wave and vertical wave velocity, compressive strength and anti-bend strength are analyzed. It has been proved that the vertical wave velocity is better for reflecting compressive strength and anti-bend strength of similar materials than the transverse wave velocity. The vertical wave velocity increases with the strengthand dynamic modulus of elasticity.

Generalized Parameters of Porous Materials as Similarity Numbers

In the multifactorial preparation of porous materials, the simultaneous/se- quential influence of a number of technological variables changes the individual parameters of the texture of the material (surface area, volume, pore size, etc.) to different values and with increase or decrease. Generalized parameters (GPs) combine these changes;new dependencies arise. GPs behave like the dimensionless similarity numbers known in science and technology (Reynolds, etc.). They split the data (phenomena) into series with similar properties, reveal special patterns and structural nuances. New GPs proposed. The average pore size is presented as the product of two GPs: the dimentionless shape factor F and pore width of unknown shape (reciprocal of the volumetric surface). Using F, for example, the SBA-15 dataset (D. Zhao, Science 1998) was split into 3 series of samples differing in synthesis temperatures, unit cell parameters, intra-wall pore volumes, pore lengths, and the ratios of wall thickness to pore size. A surprising phenomenon was discovered one of the copolymers acts in a similar way to high temperatures. The standard deviation (STD, %) of the texture parameter in the series is its serial GP. The surface topography (micropore volume per m2) is proposed;it eliminates fluctuation in material density and has a lower STD than cm3/g. Examples of the use of GPs for silica, carbon, alumina and catalysts are given. A correlation has been shown between the efficiency of some catalytic reactions (adsorption) and GPs. GPs provide new information about materials and open up new research challenges.

Experimental study on similarity materials for soft rock of deep-buried tunnels

When every parameter is properly scaled down in accordance with some similarity coefficients, it is possible to study the physical-mechanical properties of rock mass with a scale model. To identify the key mechanisms of soft rock in deep buried tunnels, the proper sand, binder and ratio were selected. During the process, the model manufacture technology was introduced and typical tests were done and the results were presented. The physical and meehanieal properties effects caused by each composition were discussed. It is shown that the physical and mechanical properties of chosen ratio material such as uniaxial compressive strength tests, elasticity modulus, tensile strength, internal frictional angle, and Poisson＇s ratio meet with similarity relationship well. The physical and mechanical properties of deep soft rock are simulated successfully.

Refill friction stir spot welding (RFSSW): a review of processing, similar/dissimilar materials joining, mechanical properties and fracture mechanism

Refill friction stir spot welding(RFSSW)provides a novel method to join similar and/or dissimilar metallic materials without a key-hole in the center of the joint.Having the key-hole free characterization,the similar/dissimilar RFSSW joint exhibits remarkable and endurable characteristics,including high shear strength,long fatigue life,and strong corrosion resistance.In the meanwhile,as the key-hole free joint has different microstructures compared with conventional friction stir spot welding,thus the RFSSW joint shall possess different shear and fatigue fracture mechanisms,which needs further investigation.To explore the underlying failure mechanism,the similar/dissimilar metallic material joining parameters and pre-treatment,mechanical properties,as well as fracture mechanisms under this novel technology will be discussed.In details,the welding tool design,welding parameters setting,and the influence of processing on the lap shear and fatigue properties,as well as the corrosion resistance will be mainly discussed.Moreover,the roadmap of RFFSW is also discussed.

Tree and shrub species preferences and planting materials used by sub-religious communities in the village groves of floodplain area of Bangladesh

An exploratory study of the traditional homestead forest of two different religious groups (Hindu and Muslim) in one selected floodplain area of Bangladesh was conducted over a period of six months from January to June 2002. The species' (both tree and shrub) preferences, similarities, use and sources of planting materials, spacing and location of species in the homesteads of both Hindu and Muslim communities were studied. It was found thatMangifera indica as tree species andOcimum sanctum as shrub species were the best preferred species of the Hindu community.Artocarpus heterophyllus as tree species andLawsonia inermis as shrub species were found best preferred by the Muslim community. Floristic similarities between the two groups were found 86.57% in tree species and 78.48% in shrub species. Both seed and seedlings of tree and shrub species as planting materials were used by the highest percentage of both the religious communities. For tree species, homegarden was reported to be the highest source (39%) and for shrub species, nature was the highest source (40%), which was found in the Hindu community. Key words Species preferences - Species similarity - Planting materials - Hindu - Muslim - Homestead forests - Floodplain area - Bangladesh CLC number S72 Document code A Biography: Md. Danesh Miah (1971): male, Assistant Professor in the Institute of Forestry and Environmental Sciences, University of Chittagong, Chittagong 4331, Bangladesh.Responsible editor: Chai Ruihai

隧道突涌水灾害缩尺物理模型试验研究综述

随着我国经济的快速发展,隧道工程建设越来越多地面临着大埋深、高地应力、高地温、高渗透压力等复杂地质环境,运用物理模型试验开展复杂环境下隧道突涌水灾变机理与安全防控研究已成为岩石力学的热点问题。结合近年来国内外针对隧道突涌水灾变缩尺物理模型试验开展的研究工作,重点对该类物理模型的流固耦合相似理论、相似材料研制、渗透压加载方法等内容进行了系统梳理,并对下一步的可能发展方向进行展望。参考部分文献和突水典型案例后,总结了流固耦合相似准则和高地应力下的相似准则、相似材料选用方案及材料配比、试验中的水压加载方案,认为未来关注的重点包括考虑温度场的物理模型试验相似准则的研究和涌水涌泥与突水突泥间渐变过程的研究2个方面。

藏东南冰碛体剪切特性受冻融循环的影响及改良

藏东南地区广泛分布着冰碛体堆积体,此土体严重影响工程安全。为了研究冰碛体的剪切性能并对其进行改良,运用相似原理配制出级配良好的冰碛体相似材料,分别在不同冻融循环次数和不同含水率的条件下,对冰碛体相似材料开展了直剪试验,同时掺入机油和粉煤灰外加剂进行三轴试验,研究其对冰碛体相似材料抗剪强度参数的影响。结果表明:(1)直剪试验过程中,随着垂直压力的增大,冰碛体的位移-剪应力曲线由弱应变软化型转变为弱应变硬化型。(2)含水率变化对冰碛体抗剪强度的升降受到冻融循环次数的影响。(3)冻融循环为5次是冰碛体材料抗剪强度的分界线。(4)机油和粉煤灰对冰碛体抗剪强度指标(咬合力和内摩擦角)的影响相反。

煤层采动底板突水物理模拟试验研究进展与展望

【目的】底板突水受特定地质构造、水-岩-应力及采掘扰动等因素叠加作用影响,具有复杂性、隐蔽性、突发性等特点。【方法】物理模拟试验能较好地还原底板岩层与承压水赋存环境、直观展现采动底板裂隙扩展及突水路径演化全过程、实时获取灾变各阶段多源数据信息,因而在底板突水研究方面具有独特优势。【结果和结论】对底板突水经典理论、标准规范、模拟试验及工程实践等方面的研究成果进行了回顾,重点梳理了试验加载装置及水压模拟方式、相似材料研制及其特性指标、监测技术及其观测系统设计3个方面的研究进展,其中在模拟水-岩-应力耦合环境下的三维模型底板突水全过程信息捕捉方面有较大突破。面对数智化研究大背景,分析当前底板突水物理模拟试验领域存在的不足,并据此指出未来应重点关注大型三维底板突水综合试验平台研制、基于标准化的多特性相似材料配比数据库建立、多相多场多维耦合监测预警系统构建、人工智能等数智化技术融合应用研究等发展方向。提出的思考有助于从装置、材料、技术等方面提升未来物理模拟试验水平,从而更好支撑煤矿底板水害数智化防治基础研究工作高质量发展。

基于正交试验的煤岩相似材料最优配比研究

目的为了探寻煤岩相似材料最优配比,方法以赵固一矿煤样的自然视密度、单轴抗压强度、弹性模量为模拟指标,采用正交设计法开展相似材料配比试验。选用碳酸钙、水泥、细河砂、煤粉、蒸馏水为原料,以骨料与胶结剂质量比、胶结剂成分间质量比、骨料成分间质量比和掺水率为控制因素,按照4因素3水平正交配比方案制备了9组相似材料。结果试验结果表明:不同配比下相似材料物理力学参数变化较大,各因素对模拟指标影响规律性强,且骨胶比对相似材料各模拟指标起控制作用,自然视密度、单轴抗压强度、弹性模量均随骨胶比增加而显著下降。通过多元线性回归分析得到相似材料最优配比为碳酸钙∶水泥∶河砂∶煤粉∶水=1∶4∶0.9∶5.8∶3.3,经验证,使用该配比制作的试样在物理力学参数、单轴压缩曲线和破坏形态上能够很好地模拟原煤。结论该研究采用理论与试验相结合的方法寻找最优配比有效可行,可为煤岩相似材料领域研究提供一定借鉴。

深埋煤层开采对河流安全性的影响评价

以文家坡煤矿4105工作面深埋覆水煤层开采为例,采用相似材料模拟和数值模拟方法,研究覆岩破坏和裂隙带发育规律,探究深埋煤层开采对红岩河安全的影响。研究表明:当工作面不断推进,采空区面积随之增加,覆岩在重力作用下发生弯曲变形,形成离层;当重力超过岩石变形极限时,覆岩会破坏变形,部分离层垮落消失,在垮落体上部发育新离层,两侧形成裂隙;4105工作面垮落带高度稳定在164 m;随着工作面的不断推进,导水裂隙带高度逐步上升,最终稳定在244 m;地裂缝自地表向下延伸32 m;导水裂隙带上方存在414 m的岩层做保护层,未导通地表,未与地裂缝沟通,因此红岩河不会发生渗漏,煤层的开采不会对红岩河产生影响。

榆神府矿区遗留房式煤柱稳定性研究

榆神府矿区大量房式煤柱遗留井下,存在煤柱尺寸偏小引发局部矿震现象。基于上河煤矿房柱式开采具体工程实际,采用理论分析、相似材料模拟实验和FLAC^(3D)计算机数值模拟分析了遗留房式煤柱稳定性状况,结果表明,遗留房式煤柱承受的上覆岩层载荷理论计算数值远小于其单轴极限抗压强度,不会出现压裂破坏;相似材料模拟实验显示遗留房式煤柱未发生宏观破坏和垮落现象,上覆地表下沉量微小;计算机数值模拟得出房式煤柱两帮虽出现微观上剪切破坏,但中部存在较大范围弹性核,不会出现整体塑性破断;因此,上河煤矿当前遗留房式煤柱整体保持稳定状态。如果煤柱与煤房尺寸反向设计开采,房式煤柱将发生明显的塑性破坏和变形,发生失稳并引发矿震现象。研究方法为榆林地区类似生产煤矿探求遗留房式煤柱的稳定性问题具有一定的借鉴意义。

一种引入元路径相似性度量的材料实体检索方法

近年来,随着材料数据的积累以及“材料基因组计划”的普及,面对大量需要处理和管理的材料数据,快速准确地检索并获取相应信息已成为一个重要问题。传统的检索方法由于仅能查询某一材料的相关信息,并且存在检索结果不全面、无法处理复杂语义关系等问题,难以获取相似程度较高的材料。为了快速、准确地找到与某种材料相似的材料,提出可度量不同节点的加权材料相似度计算模型WM-PathSim。首先,使用metapath2vec学习材料节点的嵌入表示;其次,引入TFIDF-CBOW模型学习材料路径实例的存在概率,进而计算不同元路径的权重;最后,加权求和符合条件的元路径得到最后的相似性度量,来预测不同材料之间的相似程度。在真实数据集上的结果表明,在不同的路径关系中,所提模型相比于基线方法在性能上有较大提升,其AUC和precision指标分别提升了0.37~5.02百分点和1~7.33百分点,说明所提模型得到材料间的相似程度更加准确和有效,从而能够获得相似材料。

软土地层基坑群模型试验相似材料研制及应用

针对基坑群连续开挖存在的耦合效应问题,首先确定相似材料配比方案,通过正交试验得出合理的配比材料,进而设计基坑群模型试验来研究两侧基坑叠加作用影响下车站基坑的围护结构和土体表层变形.研究结果表明:满足该软土地层相似常数的土层材料配比为(石英砂∶滑石粉∶双飞粉∶膨润土∶水=0.27∶0.27∶0.232∶0.058∶0.17);基坑群开挖时由于相邻墙体引起的墙后土拱效应叠加导致坑间土体水平应力降低,围护结构受力和变形量减小,坑间土体沉降量增大;基坑间距是支护结构变形的主要影响因素,两侧基坑间距位于1H~2H之间(H为基坑深度),接近1倍开挖深度一侧的叠加影响大于接近2倍开挖深度一侧.

基于相似理论的钢结构模型实验结果修正:以空腹梁为例

以相似理论设计大跨度钢结构缩尺模型试验时常因材料及尺寸等多参数同时畸变的问题而无法正确反映原型结构力学性能。提出了基于响应面法的响应面预测模型对畸变参数进行修正,并考虑材料加工难度及制作成本,基于相似理论设计了三种不同材料制作的1/2空腹梁缩尺模型且梁截面厚度产生畸变,对多参数畸变模型修正前后的误差进行分析。结果表明:建立的响应面方程具有很好的拟合精度和对未知参数的预测能力,在各级均布荷载作用下,多参数畸变的钢空腹梁缩尺模型通过数值模拟及等效刚度理论计算后,未经修正的缩尺模型映射原型结构的力学性能误差较大,而经过建立的响应面模型修正后,误差显著减小,多参数畸变的缩尺模型能够有效地预测原型结构的力学性能。

隧道模型试验中泥岩相似材料试验研究

隧道模型试验中选取合理的泥岩相似材料模拟围岩是试验成败的关键。为解决泥岩取样和试验中存在较大离散性和不确定性的困难,依据泥岩独特的工程地质性质,通过开展室内配合比试验,研制出可用于隧道模型试验的泥岩相似材料。结果表明:用于模拟泥岩隧道围岩的相似材料包括骨料、调节材料与胶结材料3部分;骨料是泥岩相似材料中的核心成分,包括河砂与膨润土;调节材料是模拟泥岩相似材料特征参数的关键要素,主要有铁粉和重晶石;胶结材料为石灰和石膏,胶结材料与骨料的合理配比是满足相似材料强度的主要参数;通过改变材料配比,得到了满足泥岩相似材料力学指标的配合比,试验结果可为制备模拟隧道围岩的泥岩相似材料提供一定参考。