Prediction of thermal conductivity of rocks by soft computing

The transfer of energy between two adjacent parts of rock mainly depends on its thermal conductivity. Knowledge of the thermal conductivity of rocks is necessary for the calculation of heat flow or for the longtime modeling of geothermal resources. In recent years, considerable effort has been made to develop artificial intelligence techniques to determine these properties. Present study supports the application of artificial neural network (ANN) in the study of thermal conductivity along with other intrinsic properties of rock due to its increasing importance in many areas of rock engineering, agronomy, and geoenvironmental engineering field. In this paper, an attempt has been made to predict the thermal conductivity (TC) of rocks by incorporating uniaxial compressive strength, density, porosity, and P-wave velocity using artificial neural network (ANN) technique. A three-layer feed forward back propagation neural network with 4-7-1 architecture was trained and tested using 107 experimental data sets of various rocks. Twenty new data sets were used for the validation and comparison of the TC by ANN. Multivariate regression analysis (MVRA) has also been done with same data sets of ANN. ANN and MVRA results were compared based on coefficient of determination (CoD) and mean absolute error (MAE) between experimental and predicted values of TC. It was found that CoD between measured and predicted values of TC by ANN and MVRA were 0.984 and 0.914, respectively, whereas MAE was 0.0894 and 0.2085 for ANN and MVRA, respectively.     

天津地区浅层地热能赋存条件浅析及前景展望

通过对地质、钻探资料和物探测井、岩土体热物性参数测试等资料的研究,结合综合勘查技术方法和对已有资料的二次开发,查明了天津地区浅层地热能赋存条件,尤其是岩土体的热物理参数变化规律,并借助Excel办公软件,采用数理统计方法对岩土体热物性参数的变化进行了分析。结果表明区内岩土体的热导率为1.23~1.62 W/(m·℃),比热容为1898.52~2201.70 J/(kg·K);粘土和粉质粘土含水量在19%左右时热导率最佳,粉土和粉砂含水量在17%左右时热导率最佳。该区浅层地热能赋存丰富,具有很广阔的开发前景。     

The effects of strain rate and saturation on a micro-cracked marble

It is well known rock masses contain several types of weakness planes varying from micro-fissure to fault in size. The fracture frequency, degree of saturation and time are the basic rock parameters affecting its behaviour. However, in most cases, it is practically difficult to test heavily fractured rock in laboratory environment. In this study, the effects of micro cracks, strain rate and water saturation on strength are discussed using a small-scale physical experiments. It is attempted to detach the grain boundaries of coarse-grained rock specimens of the Mu?la marble by thermal treatment that would serve as a small-scale physical simulation of fractures in rock masses and enable a discussion of the variations in time dependent mechanical behaviour. An experimental study was conducted on marble specimens induced thermally by micro-cracks in different frequencies. The thermal treatment periods being 24 h in inert atmospheric condition were varied for each test specimen except categories A and G. Effective porosity increased up to 2.4% after the last thermal cycle of category F. Then conventional compression tests with different strain rates were carried out using a servo-controlled testing machine on both dry and saturated specimens. It is concluded that both lowering strain rates and increasing porosity related with thermally induced micro cracks have important effects on strength and failure path. The progressive failure entirely occurs along the grain boundaries fissured by cyclical treatment and inter-granular deformation depends upon degree of thermal influence. The small-scaled laboratory model enabled to demonstrate that parameters such as joint frequency, time and saturation have a significant effect on mechanical behaviour of rock masses.     

The potential use of serpentinite in the passive treatment of acid mine drainage: batch experiments

The efficiency of serpentinite as an alternative alkalinity generating material for the passive treatment of acid mine drainage (AMD) was assessed in the laboratory. Three series of batch experiments were designed for the passive treatment of a low pH (1.6) AMD synthetic solution containing 2,500 ppm Fe²⁺, 6,600 ppm SO₄^2–, 10.5 ppm Al, 15 ppm Ni, and traces of Cr, Mn and Cu. The influencing factors studied were: the effect of water/rock ratio, residence time, type of the alkalinity generating material (dolomite, magnesite, marble, serpentinite), and nature of the system (open vs. closed cells). The variations in solution chemistry observed in the open cells indicate that a lower water/rock ratio (0.33 ml/g) was the most efficient for metals removal. The optimal residence time in open cells was 24 h to reach the higher pH values. In the closed cells laboratory setup, synthetic AMD was placed in contact with the various alkaline materials for three different contact times (24, 48, 72 h). The optimal pH was reached after 48 h and did not change appreciably for longer contact time, and the best results for metal removals were obtained with marble and serpentinite. Single treatment efficiency was compared with a successive treatment approach. The most promising results were obtained with a five step treatment: (1) pre-treatment in a closed cell using serpentinite, (2) aeration and settling, (3) treatment in an open cell using marble, (4) final aeration and settling, and (5) filtration with a coarse silica sand. With this configuration, the final pH was 6.5 and pronounced metals depletion was achieved (100% for Al, 99.95% for Fe, 85.7% for Ni).     

低应力下岩石裂隙水力特性

针对地表附近30～50 m的岩体裂隙处于一种低围压状态（约1 MPa左右）这一情况,提出了低应力状态下裂隙变形的两点假设：（1）裂隙面处于线弹性状态;（2）隙宽减小量相对于初始力学隙宽是一个微小量。结合Barton公式,建立了低法向应力下裂隙渗流的半经验理论公式,并从实验的角度验证了该公式的合理性。实验结果和理论分析表明：低法向应力作用下,裂隙渗透系数随法向应力的增加而线性降低。此外,给出了一种间接确定裂隙初始力学隙宽的方法。     

高温循环作用后大理岩裂纹扩展试验研究

利用偏光显微镜对经历不同高温循环作用后的细粒大理岩进行观测,通过统计微裂纹长度、开度、数量等参数,探讨不同加热循环次数后岩样内微裂纹的扩展规律。结果表明,（1）经历不同热循环次数作用的岩样,微裂纹的数量和长度均不同,未经热处理岩样内颗粒致密,胶结较好,内部无明显的微裂纹。经历4次热循环作用后岩样内微裂纹发育明显,以晶界裂纹为主,开度和长度均显著增加。岩样经历16次热循环作用后开度持续增大,为55 µm,是4次热循环的4倍;（2）对不同热循环处理后岩样内部发育微裂纹的方向进行了统计,发现微裂纹无明显的方向性,还表明细观切片的取样位置对微裂纹的发育影响不大;（3）线性裂纹密度随热循环次数的增加而增大,经历16次热循环作用后岩样的线性裂纹密度是没有经历热处理岩样的21倍。     

岩土体综合导热系数影响因素研究

为缓解中国能源消耗与经济发展的矛盾,高效调整国家能源结构,开发利用绿色的地热能已是大势所趋。通过室内测试法和现场热响应试验,研究了不同岩土体的导热系数特征值及其影响因素。研究结果表明: 岩土体导热系数与天然含水率和孔隙率呈负相关,与天然重度和干燥重度呈正相关; 导热系数受干燥重度和孔隙率影响程度较大,受天然含水率和天然重度影响程度较小。通过比较不同加热功率和单、双U地埋管换热器的现场热响应试验测定的各类岩土体导热系数的差异可知,大功率(6 000 W)情况下岩土体综合导热系数比小功率(4 000 W)时大10%~30%; 在相同功率条件下,同一场地内双U地埋管换热器导热系数比单U地埋管大30%左右,使用双U地埋管换热器可有效减少成孔深度及个数。通过系统分析岩土体导热系数的影响因素,为地热能的勘查评价提供数据和理论支持,旨在促进区域地热能开发利用,为构建环境友好型社会服务。     

地热-Ⅰ型热导仪实验室间互检及改进

作者于1980年访美期间,通过样品的成组对比测试,将我国自行试制的地热-Ⅰ型岩石热导仪与美国地质调查所西部总部地热实验室的改型分棒仪,进行实验室间的互检,历时近三个月。对比结果,既肯定了地热-Ⅰ型热导仪的总体适用性,同时也揭示了几项误差因子,为我实验室尽快筹建地热-Ⅱ型热导仪提出了改进方向和设计依据。本文简要报道互检结果及对各项误差因子的分析。     

利用超高压变质岩的P波速度估算地下岩石的热导率

岩石热导率是了解地球内部热传导过程的重要参数之一, 但热导率的测量在室内和野外都比较复杂.如何利用容易获得的岩石物理参数(如超声波速度) 来估算岩石的热导率就显得非常重要.通过对中国大陆科学钻探(CCSD) 主孔655件样品热导率和超声波速度的相关分析, 把样品分为新鲜榴辉岩、退变质榴辉岩、副片麻岩和正片麻岩4类, 并分别建立了利用岩石P波速度估算热导率的计算方程.回归计算表明, 榴辉岩热导率和P波速度之间的相关性较大, 相关系数在0.7左右, 片麻岩显示的相关系数比较小, 在0.4~0.5之间.鉴于样本数量较大, 这种结果足以表明热导率和P波速度之间可以用给定的线性关系来表达.为了检验获得的方程, 在CCSD主孔中选取典型的岩性单元, 利用测得的P波速度估算相应的热导率, 结果显示估算值和实测热导率平均值非常接近, 表明利用P波估算岩石热导率的方程是可行和实用的, 为本区和相似地区大地热流和热结构计算提供了热导率的计算方法和依据, 因而具有重要的岩石物理学和地球物理意义.      

Marble decay induced by thermal strains: simulations and experiments

Thermoelastic behavior of different marble types was analyzed using computational modeling and experimental measurements. Eight marble samples with different composition, grain size, grain boundary geometry, and texture were investigated. Calcitic and dolomitic marbles were considered. The average grain size varies from 75 μm to 1.75 mm; grain boundary geometry differs from nearly equigranular straight grain boundaries to inequigranular-interlobate grain boundaries. Four typical marble texture types were observed by EBSD measurements: weak texture; strong texture; girdle texture and high-temperature texture. These crystallographic orientations were used in conjunction with microstructure-based finite element analysis to compute the thermoelastic responses of marble upon heating. Microstructural response maps highlight regions and conditions in the marble fabric that are susceptible to degradation phenomena. This behavior was compared to the measured thermal expansion behavior, which shows increasing residual strains upon repetitive heating–cooling cycles. The thermal expansion behavior as a function of temperature changes can be classified into four categories: (a) isotropic thermal expansion with small or no residual strain; (b) anisotropic thermal expansion with small or no residual strain; (c) isotropic thermal expansion with a residual strain; and (d) anisotropic thermal expansion with residual strain. Thermal expansion coefficients were calculated for both simulated and experimental data and also modeled from the texture using the MTEX software. Fabric parameters control the amount and directional dependence of the thermal expansion. Marbles with strong texture show higher directional dependence of the thermal expansion coefficients and have smaller microstructural values of the maximum principal stress and strain energy density, the main precursors of microcracking throughout the marble fabric. In contrast, marbles with weak texture show isotropic thermal expansion behavior, have a higher propensity to microcracking, and exhibit higher values of maximum principal stress and strain energy density. Good agreement between the experimental and computational results is observed, demonstrating that microstructure-based finite-element simulations are an excellent tool for elucidating influences of rock fabric on thermoelastic behavior.     

南方地区城市生活垃圾导热系数的试验研究

温度场对垃圾填埋场的衬垫系统、气体运移和垃圾土工程特性等存在显著影响,导热系数是研究填埋场内温度场的重要参数。以台州卢岙里垃圾填埋场为研究对象,采用DRCD-3030型智能化导热系数测定仪,测定了不同孔隙率和含水率条件下的垃圾导热系数。试验中,垃圾试样的含水率分别取0%、5%、10%、15%、20%、25%、30%、35%、40%、45%和50%;垃圾的孔隙率分别取77.8%、75.0%、71.4%和66.7%。试验结果表明：干垃圾导热系数较小,仅为标准状态空气导热系数的2.5～3.5倍,并随孔隙率的增大而减小;非饱和垃圾的导热系数随含水率的增加而增大,当含水率相等时,孔隙率越小,垃圾的导热系数越大。根据垃圾导热系数的实测数据,利用修正几何加权平均模型和线性拟合技术,建立了垃圾导热系数的计算公式,可以为垃圾填埋场温度场的研究提供重要参考。     

两淮煤田煤系地层岩石热导率特征

基于对淮北和淮南煤田煤系地层所测定的127块岩石样品的热导率结果,对测试的岩石热导率结果进行校正,还原 岩石初始压力和温度环境下的热导率,校正结果值略大于实测值。同时结合区内前人的实测数据,全面报道了两淮煤田岩 石热导率参数及其特征,并从多方面分析了影响热导率大小的因素。结果表明：两淮煤田煤系地层岩石热导率变化范围为0.37～ 4.36 W/mK,平均值2.54 W/mK;热导率与岩性、埋藏深度、地层时代和密度等相关密切,砂岩的热导率普遍大于泥岩和 煤,热导率和深度、密度均表现为正相关关系。     

江苏干热岩地热资源潜力估算

干热岩是一种清洁的可再生地热资源,随着开发技术日趋成熟,显示出其巨大的利用价值。江苏地区中、新生代发 育大量火山活动,深部热源上涌,具有良好的干热岩赋存背景。文中在对江苏地区大地热流值、不同深度岩石热导率、生 热率分析的基础上,利用贡献率叠加法,对苏北盆地与苏南地区不同深度的温度进行估算,将5~8 km的温度计算结果与采 用温度梯度计算方法所得数据进行对比分析,在此基础上对江苏地区3 km至8 km深处干热岩资源量进行预测。结果显示, 江苏地区3~8 km深处干热岩资源总计为2.18×1021 J,合74.9亿吨标准煤,按2%的可开采资源量计算,即合1.5×108 t标准 煤,约相当于江苏省一年能源消耗总量的一半,开发利用前景巨大。     

松辽盆地北部岩石热导率及其影响因素

本次研究采用瞬态平面源法对松辽盆地北部76个钻孔的263个岩心样品进行了岩石热导率测试。岩心的实测热导率集中在0.58~3.00 W/(m·K)之间, 平均为(1.77±0.64) W/(m·K); 泥岩、粉砂岩、砂岩、砾岩平均热导率分别为(1.30±0.39) W/(m·K)、(1.89±0.64) W/(m·K)、(1.91±0.37) W/(m·K)、(2.18±0.57) W/(m·K); 变质岩、火成岩平均热导率分别为(2.75±0.67) W/(m·K)、(2.70±0.45) W/(m·K)。碎屑岩和凝灰岩热导率整体上呈现出随着埋深和地层年龄的增加而增大的趋势, 而砾岩和变质岩变化趋势不明显。分析了压实成岩作用、砂岩的矿物含量和岩石的变质作用对岩石热导率造成的影响。通过饱水测量获得了原位热导率, 对岩心的原位导热系数进行了修正。最后建立了松辽盆地北部地层热导率柱, 可以为研究区的热流计算、深部地温场建模、盆地热史恢复等提供地层热导率约束。     

岩土体导热系数研究进展

岩土体导热系数在与地热有关的地质基础研究和生产应用中有重要作用。首先介绍了导热系数的概念,然后分析了导热系数的受控因素,最后探讨了导热系数的测定方法。导热系数的受控因素包括地层岩性、孔隙率、含水率、温度以及各向异性。导热系数随地层岩性从大到小排列为海相碳酸盐岩、陆相碎屑岩、火成岩,变质岩导热系数与母岩和变质程度有关;同种岩层的导热系数随沉积过程延续或深度增加而增大;含水率对软弱岩石的导热系数影响较大,导热系数随含水率增大而增大,对孔隙度较大的岩层需进行饱水校正;不同岩性的导热系数随温度的变化较复杂,在应用中需结合实际地层考虑;由于结构面的存在,岩体的导热系数存在各向异性。导热系数的测定方法包括现场测试法、室内测试法、组分类型辨别法以及利用P波速度估算等。利用现场数据求解导热系数时常使用线热源模型和柱热源模型;室内测试法包括稳态测试法和非稳态测试法,分别应用于中低导热系数材料和高导热系数材料;对于组分类型辨别法,平行板式相分布的物体导热系数是各向不等的,热传导方向与平行板平面平行和垂直时分别具有最小和最大总体导热系数;对地下无法直接测量的地质单元,可利用P波速度估算导热系数。要得到准确的导热系数,须基于岩土体的导热系数范围和样品特征选取正确的测定方法。     

温度周期作用下大理岩三轴蠕变试验与理论模型研究

为了解温度周期作用对大理岩蠕变力学特性的影响,采用温度-应力-渗流耦合的岩石力学三轴流变试验系统对大理岩进行了不同温度及温度周期变化下三轴压缩蠕变试验。基于试验结果,研究了大理岩试样在不同温度及温度周期变化下轴向应变随时间的变化规律,分析了不同温度及温度周期变化下蠕变的变形机制,掌握了温度对大理岩三轴蠕变影响的基本规律,并且建立了考虑温度及温度周期变化影响的改进的Burgers模型。理论值与试验结果非常接近,表明考虑温度及温度周期变化的改进Burgers模型适合描述大理岩的黏弹性蠕变特征。为长期暴露于外部环境下的岩质边坡的长期稳定性分析提供了重要的参考依据。     

关于岩石导热性野外测定方法的研究

导热系数是岩石重要的物理参数之一,其在地热能开发及岩土热工程应用中有着重要意义.目前的测试方法需要将岩样采回实验室进行表面加工,运输和加工过程会破坏岩石结构和影响含水率等,不仅测试工艺复杂,而且导致测试结果不准确.本研究提出一种现场获取岩石导热系数的新方法.利用导热耦合剂填充岩石表面与探头之间的接触面,减小测试过程中的接触热阻,辅助热物性测试仪器来开展野外导热系数测试工作.通过配制不同导热硅脂与不同铜粉掺量充分混合的导热耦合剂进行对比实验,确定导热耦合剂的最优配比.实验表明,导热耦合剂的涂抹能有效地减小探头与岩石表面的接触热阻,提高测试精度,且导热耦合剂本身对岩石的导热系数影响甚微.研究成果可为野外准确便捷地获得岩石导热系数提供参考.     

重庆永川煤矿煤岩热物性参数特征

煤岩热物性参数是矿井降温、防灭火治理工作所需要的重要基础资料。以重庆永川煤矿为研究对象,采用井下现场测定和实验室测试对该矿目前采掘区域内煤岩密度、比热、导热系数、导温系数以及原始温度、地温梯度等参数进行了测试。测试结果表明,在矿井标高-400 m水平,煤岩样的密度、比热、导热系数、导温系数均处在正常范围之内;在标高-357~-438 m,煤岩密度、比热、导热系数、导温系数不随标高的变化而变化。在标高-400 m水平,煤岩原始温度为35~36℃;矿井恒温带深度以下,-400 m水平以上的地温梯度为2.32/℃ hm,-400 m水平以下的地温梯度值为2.65/℃ hm,存在一个稍微递增的趋势,但仍然处于正常地温梯度范围。结合矿井地勘资料确定煤岩原始温度的实测值较理论计算值偏小,但误差不超过3%,精度符合工程实际要求。     

大理岩非线性蠕变模型研究

为了认识大理岩蠕变特性,采用RLW-1000G岩石三轴流变仪对西安市长安县天赐山大理岩进行了一系列不同加载时间下的单轴蠕变试验,并应用改进的西原模型对蠕变试验曲线进行辨识。试验表明：大理岩轴向变形过程中瞬时变形、等速蠕变及加速蠕变较为明显,减速蠕变历程极短; 大理岩在同级荷载作用下,随着加载时间增长,其损伤效应加剧,导致相应的应变增量增大。应用非线性的黏滞元件对西原模型进行改进,得到了大理岩复合流变模型,并应用大理岩蠕变试验数据对该模型进行拟合分析,取得了较好的效果。 研究结果对认识大理岩蠕变特性及对岩体工程建设具有一定的指导意义。     

X射线荧光光谱分析技术在大理岩鉴定与分类中的应用

大理岩的鉴定与分类主要依靠岩石薄片鉴定及X射线衍射(XRD)矿物半定量检测技术。工作中发现,岩石薄片鉴定技术及XRD矿物半定量检测技术所测得矿物组分含量很少一致,这就需要引入其他技术对岩石薄片鉴定及XRD矿物半定量检测结果加以验证。本文利用X射线荧光光谱仪(XRF)对野外采集的32件大理岩样品进行全岩化学成分分析,以岩石化学成分为基础,分析岩石杂质系数、镁质系数和钙质系数特征,对大理岩进行分类。结果表明:方解石大理岩、白云石大理岩、菱镁矿大理岩的镁质系数值分别为0.01~0.13、0.40~0.46、0.97~0.98,钙质系数值分别为0.78~0.84、0.30~0.49和0.01~0.02,不同类型大理岩的钙质系数和镁质系数明显不同,可以作为划分大理岩类型的主要依据。当岩石中SiO_2+Al_2O_3含量大于35%(杂质系数大于为1.20),不能定为大理岩,只有岩石中SiO_2+Al_2O_3含量小于30%(杂质系数小于1.00)时,可定为大理岩。杂质系数、镁质系数和钙质系数的应用,能够校正岩石薄片鉴定法及XRD矿物半定量法矿物含量检测不一致的问题,使大理岩分类定名更加准确。