核废料储库周边介质热力耦合数值分析

以热力学和热弹性理论为基础,分析热-力相互耦合作用及其对热特性参数和力特性参数的影响。建立了非等温条件下的耦合作用控制方程,给出了相应的空间离散和时间离散形式。利用有限元法对一核废料储库的平面问题进行了计算,讨论了储库周围粘性土介质内温度场、应力场等的动态发展变化规律,并分析了耦合效应对计算结果的影响。研究表明,随时间的增长,热能由储库边壁不断向远处传导和扩散,而在空间上又处于不断变化的非等温状态,这一动态变化过程必然会诱致周围土介质内应力的产生和发展,并随温度的变化而不断变化。     

温度对非饱和土抗剪强度影响的试验研究

在室内试验的基础上,对不同含水量和干密度的粘性土试样进行了不同环境温度下的直剪试验,获得了南京地区非饱和下蜀土重塑土抗剪强度与温度的关系.试验结果表明:温度对粘性土的抗剪强度有比较复杂的影响.当含水量大于约18%时,土的抗剪强度随着温度的升高而降低,表现出强度的热软化现象;而当含水量等于或低于18%时,土的抗剪强度在干密度等于1.67g·cm-3时,几乎不受温度影响,而当干密度小于1.67 g·cm-3时,土的抗剪强度随着温度的升高而增加,呈现出强度的热同结现象.与此同时,还对土的热固结和热软化现象的机理进行了分析.     

热-力耦合作用下垃圾土体积变形特性和模型研究

城市生活垃圾填埋场因有机质降解产热导致其内部温度长期高于环境温度,引发工程运维问题。垃圾土温控三轴试验结果发现,温度变化引起的垃圾土体积应变与应力水平有关,且弹性体积应变占比较大,影响以塑性体积应变为硬化参数的弹塑性本构模型研究。在前期试验基础上,采用GDS温控应力路径三轴仪,研究了排水条件下温度对垃圾土中黏土体积变形特性和压缩特性的影响,并与相同条件下垃圾土体积变形特性进行比较,揭示了温度变化对垃圾土体积变形特性的影响机制。基于垃圾土温控三轴试验结果,推导了垃圾土热弹塑性压缩指数λ_T和热弹性压缩指数κ_T的确定方法;采用等效应力原则,假设温度变化引起的弹塑性体积应变等于某一等效应力增量引起的弹塑性体积应变,建立了垃圾土在热-力耦合作用下的体变计算模型,并对模型进行了验证分析。研究结果表明,孔隙比是影响垃圾土温度体积应变的主要因素;垃圾土的λ_T和κ_T随初始固结应力的增加而减小,比黏土高一个数量级;选取常温下相应固结应力水平的回弹指数κ和压缩指数λ比例值(κ/λ)能够较好地模拟热-力耦合作用下垃圾土的体...     

热-水-力耦合作用下非饱和土变形特性的弹塑性模拟

在已有的非饱和土水-力耦合模型基础上,耦合考虑温度影响,建立了一个热-水-力耦合作用下非饱和土弹塑性本构模型。该模型以土骨架平均应力、修正吸力和温度为应力状态变量,以土骨架应变、饱和度和熵为应变状态变量。通过引入与温度相关的屈服面(LY、TY)以及相应的硬化规律来考虑温度对土体变形的影响。利用建立的模型,对文献中不同吸力和温度条件下的等向压缩和三轴排水剪切试验进行预测,预测结果表明,该模型能够较好地定量描述热-水-力耦合作用下非饱和土的变形特性。     

包气带粘性土层防污性能研究

包气带粘性土的特性及其分布规律是影响污染物自然衰减的重要因素。在分析粘性土类型和粘性土防污机理的基础上,探讨了微生物等因素对粘性土防污效果的影响,指出目前包气带粘性土防污研究中存在的若干问题。3S技术、ADM非确定理论有助于解决研究尺度偏小、量化指标不足的问题,多学科交叉复合将是包气带粘性土层防污研究的必然发展趋势。     

非饱和土中热弹性波的传播特性分析

基于非饱和多孔介质的研究成果,考虑热效应和孔隙流体迂曲度的影响,研究了非饱和土中热弹性波的传播特性。利用非饱和土中耦合热的固-液-气三相介质的质量平衡方程、渗流连续方程、动量平衡方程和广义非Fourier热传导定律,建立了问题的热弹性波动方程。通过引入势函数,经过理论推导给出了非饱和土中热弹性波的弥散特征方程。结合数值算例,分析了几类热弹性波的波速和衰减系数随迂曲度、热膨胀系数和介质温度等热物理参数的变化规律。结果表明：孔隙水迂曲度的增大将引起P1波、P3波和S波的波速增大,而孔隙气体迂曲度的增大仅使得P2波的波速增大;热膨胀系数的增大将造成P1波波速的增大和热（T）波波速的减小;介质温度的升高将引起各类热弹性波波速的增大;频率、热膨胀系数和介质温度的变化对各类热弹性波的衰减系数均有较大影响,不可忽视。     

空心圆柱饱和多孔介质热固结问题的解析解

基于考虑热渗效应和等温热流效应的热-水-力耦合的线性热弹性固结控制方程,建立无限长空心圆柱饱和多孔介质热固结问题的一种理论求解方法。该方法先给出Laplace变换域上的解,然后,利用Stehfest法求其数值逆变换。该理论解考虑了空心圆柱体内、外透水界面随时间变化的外力和温度荷载耦合作用过程。最后,通过一算例分析了饱和多孔介质的热固结特征,给出其温度、孔压、位移和应力的演化规律     

温度作用下缺陷花岗岩热损伤:以甘肃北山缺陷花岗岩为例

为了研究温度作用下缺陷花岗岩的热损伤问题,以甘肃北山缺陷花岗岩为例,从损伤力学和热力学的角度出发,研究了缺陷花岗岩内部热应力的产生机理,推导出缺陷花岗岩裂纹热损伤的临界应力公式,分析了高温作用对花岗岩热弹性比能变化的影响规律,建立了温度作用下花岗岩热损伤演化方程,并对温度作用下花岗岩应力损伤面可能存在的形态进行了研究。对含缺陷的花岗岩在温度作用下结构内部结构晶体单元损伤、晶体单元损伤应力变化规律进行数值模拟,结果表明:当模拟温度升高到60℃时,花岗岩缺陷裂纹附近出现明显的热损伤,远离缺陷处出现微弱的热损伤;当温度升高到120℃时,花岗岩缺陷处剪切破坏特征明显,裂纹处的热损伤点继续增大,远离缺陷处出现非常明显的不间断损伤点,损伤量、热应力、能量累计数出现了突变;此后,随着温度升高到200℃,损伤增量变化微弱。北山缺陷花岗岩的损伤量和温度之间存在直接的演化关系。     

路基土体“锅盖效应”的数值模拟分析

基于对道面下路基土体中"锅盖效应"形成机制的定性认识,依据非饱和土中气液传输及热传导多场耦合理论并考虑水的气液相转换,建议了对此问题进行分析的数学模型。采用有限元方法对道面下路基一维土柱进行模拟分析,揭示了土中水和水蒸气在变温作用下的运移及相变规律,分析了"锅盖效应"形成条件和影响因素。数值结果显示,土质和温度分布对路基土发生"锅盖效应"有较大影响。粉土路基较黏土或砂土路基更易形成水分聚集;路基顶部温度较路基深处温度低时,在温度作用下易引起路基土的"锅盖效应"。这些结果可为进一步研究道路工程中的"锅盖效应"提供参考。     

填埋场粘土类防渗系统研究进展

作为防止污染物扩散的防渗系统是填埋场中最重要的部分之一。在总结国内外众多有关填埋场粘性土防渗系统研究成果的基础上,阐述了粘土类防渗系统的工作机理;从粘性土阻滞特性、污染物运移、改性与替代材料以及防渗系统设计等4个方面综述了粘土类防渗系统研究的最新进展;并据此认为,非饱和渗透特性、吸附效应及基于吸附－扩散效应的设计方法等将成为今后填埋场粘性土防渗系统研究的主要问题。     

Experimental study of thermal effects on the mechanical behaviour of a clay

The paper presents the results of an experimental study of thermal effects on the mechanical behaviour of a saturated clay. The study was performed on CM clay (Kaolin) using a temperature-controlled triaxial apparatus. Applied temperatures were between 22 and 90°C. A comprehensive experimental program was carried out, including: (i) triaxial shear tests at ambient and high temperatures for different initial overconsolidation ratios; (ii) consolidation tests at ambient and high temperatures; and (iii) drained thermal heating for different initial overconsolidation ratios. The obtained results provide observations concerning a wide scope of the thermo-mechanical behaviour of clays. Test results obtained at 90°C were compared with tests performed at ambient temperature. Based on these comparisons, thermal effects on a variety of features of behaviour are presented and discussed. Focus is made on: (i) induced thermal volume change during drained heating; (ii) experimental evidence of temperature influence on preconsolidation pressure and on compressibility index; (iii) thermal effects on shear strength and critical state; and (iv) thermal effects on elastic modulus. Thermal yielding is discussed and yield limit evolution with temperature is presented. The directions of the induced plastic strains are also discussed. Several remarks on the difference in the mechanical behaviour at ambient and high temperatures conclude the paper. Copyright © 2004 John Wiley & Sons, Ltd.     

考虑温度影响的重塑非饱和膨胀土非线性本构模型

以非饱和土的非线性模型为基础,通过对土性参数的修正和考虑温度本身引起的土的变形,建立了考虑温度效应的重塑非饱和膨胀土的本构模型。该模型包括土骨架的本构关系和水量变化的本构关系两个方面,涉及18个参数,都可用非饱和土三轴试验确定。共做了13个重塑非饱和膨胀土温控三轴试验,分析了温度对土的强度和变形的影响,研究了模型参数的变化规律。     

黏土地基中能量桩力学特性数值分析

能量桩是将地源热泵系统中的换热管埋置在桩体内部,桩同时起到承载和换热的作用,是一种新型的基础型式。为了合理分析黏土地基中能量桩的力学特性,需要了解能量桩运行过程中桩和地基土的温度响应,并考虑温度变化对土体力学性能的影响。基于有限元软件ABAQUS建立了能量桩传热分析三维有限元模型,把能量桩的传热简化为换热管内液体与管壁之间的对流传热、桩体中的热传导和地基中的热传导,将计算结果与常规理论和实测数据进行了对比验证。对热力耦合边界面本构模型进行了二次开发,通过算例验证了模型对土体压缩和剪切性状温度效应的模拟能力。利用所提出的能量桩传热分析方法和热边界面模型,考虑不同的桩顶工作荷载水平,对正常固结黏土地基中能量桩单桩的长期性能进行了研究,分析了温度循环对桩顶沉降、桩侧摩阻力和桩身轴力的影响。结果表明,工作荷载越高,温度循环次数越多,桩顶累积沉降越大。     

寒区渠基黏土热参数最优概率分布

为分析寒区渠基黏土热参数的随机分布特征及概率分布模型,以寒区渠基黏土的导热系数为样本,结合经典分布拟合法、多项式逼近法、最大熵法和正态信息扩散法,分别对寒区渠基黏土热参数的概率分布规律进行了研究。首先通过分析热参数的离散性,并比较概率分布曲线、拟合检验值和累计概率分布值,对不同方法描述热参数随机性的优劣进行了评价;然后,基于寒区渠基黏土热学参数对温度的敏感性,提出了一个可以达到理想拟合精度的寒区渠基黏土热参数概率推断的区间取值标准。研究结果表明：寒区渠基黏土的热参数具有随机变量的特征;正态信息扩散法可以描述热参数样本的随机波动性;在4种方法中,正态信息扩散法的拟合精度最高。使用3.5σ法,将[μ-3.5σ,μ+3.5σ]（μ为随机变量的均值,σ为标准差）作为概率函数推断时的取值区间,同时考虑偏度的影响,可使得累计概率值达到1.000 0的精度,能够较准确地推断热参数的概率分布函数。     

Magnitude of latent heat in thermally loaded clays

Temperature changes are known to induce specific couplings in clay, in particular, an anomalously high thermal pressurization in undrained conditions or a thermal compaction in drained conditions, both of which are potential threats for the mechanical stability and sealing capacity of the geomaterials. Thermodynamical analysis of those peculiar thermomechanical couplings points to a potentially important latent energy, which in turn could limit the temperature change upon heating or cooling. The direct measurement of latent energy developed during a laboratory geomechanical test is challenging. Instead, proper identification of thermal hardening in conventional experiments with temperature changes provides an alternative route to estimate latent energy. In this work, existing laboratory thermomechanical tests of clays are analyzed with a rigorous thermodynamic framework to quantify the magnitude of latent energy in thermomechanically loaded clays. A thermodynamically consistent constitutive model for fully saturated clays that combines two key features, (a) the temperature dependence of the blocked energy and (b) the framework of bounding plasticity, is proposed. The performance of the model is validated by reproducing results obtained in laboratory tests for Boom and Opalinus clays. The thermomechanical loads considered to validate the model performance were then used to estimate the percentage of work that remains latent in the clayey material during plastic yielding. We find that the magnitude of latent energy is quite significant, typically a few tens of percent of the total dissipated energy, and increases significantly with temperature. Accordingly, it is expected to play an important role in the thermomechanical response of clays.     

Effect of dry density,soil texture and time-spatial variable water content on the soil thermal conductivity

Study of the heat transfer process in saturated and unsaturated soils requires, basically, a relationship between thermal conductivity and the characteristics of the soil, such as water content, dry density and texture of the soil. This study intends to produce a generic model that can predict soil thermal conductivity with the help of easily measurable parameters. The proposed model is first calibrated using measured thermal conductivities from literature data. In order to validate the proposed model the predicted thermal conductivity of this proposed model as well as existing ones are compared with the measured thermal conductivity in literature for different soils. Validation of the proposed model was also performed on our experimental results obtained for a compacted Misillac sand and in-situ clay loam soils. The results show an average of 15% improvement in prediction accuracy for the proposed model compared to the existing models, considering all soil textures. Moreover, we perform a model to estimate thermal conductivity over time throughout the profile of soil in the context of seasonal variation of temperature. The proposed model shows an important effect of heterogeneity on the thermal conductivity variations of a double layered soil.     

Thermo-hydro-mechanical behaviour of two heavily overconsolidated clays

An experimental study on the thermo-hydro-mechanical behaviour of two heavily overconsolidated clays is presented. Laboratory tests have been conducted on a Spanish bentonite (FEBEX bentonite) and a Belgian kaolinitic/illitic clay (Boom clay), statically compacted at different initial dry densities and water contents. Volume change behaviour of the soils during suction reduction paths at different temperatures and during heating-cooling cycles at constant water content or suction have been investigated through the use of suction and temperature controlled oedometer cells. In addition, the volume change response under unconfined conditions and constant water content has been measured to determine thermal expansion coefficients. The results show similarities and differences between the observed behaviour of the two types of clays that have been interpreted on the basis of their different structures and regarding their proportion of intra-aggregate water.     

砾石地层冻土热物理特性研究

地铁建设中时有穿越富含砾石的地层,需使用冻结法施工,而砾石地层的热物理性质是冻结法设计的重要依据。为研究人工冻结砾石土热物理特性,通过自制试验仪器,开展了砾石土冻结温度、导热系数和容积热容量测定方法及其特性研究,并与黏土、粉土等典型土层进行对比分析。结果表明:砾石土冻结温度曲线变化符合常规变化规律,且冻结温度为-0.21 ℃,高于黏土、粉土等;砾石土容积热容量与黏土、粉土等相近,随颗粒粒径增大,常温和冻结状态下土体容积热容量比值减小,其中砾石土的比值为1.19;砾石土导热系数较大,冻结状态下达3.89 W/(m·k),是常温状态下的1.65倍,符合颗粒粒径对导热系数的影响规律。砾石土导热系数可按各组成物质的导热系数及其相应的体积比推算。     

不同温度应力路径下饱和黏土剪切特性

在精准温控动三轴试验系统上开展了不同温度及不同升温路径饱和黏土剪切试验研究,探讨了不同温度对饱和软黏土不排水剪切特性的影响,分析不同升温固结方式对饱和软黏土孔压发展、体变、强度以及模量的影响规律。试验结果显示：在4～76 ℃试验研究范围内,环境温度升高导致饱和软黏土的不排水剪切强度有所减少,但温度升高对土体模量增加影响明显,温度T和模量ET关系可用ET = 2.69T 0.3表达;升温变化时正常固结黏土产生超孔隙水压力并随着温度增大而增大,升温热固结后土的剪切强度将明显提高,且排水状态下升温固结对土剪切强度增长小于升温完成后再固结情况;土体从26 ℃分别升高20、40 ℃时,升温引起的超孔压比分别为0.41、0.61,剪切峰值强度分别增加8.23%、22.37%。研究表明：升温幅值增大会使土体热固结程度越大,升温分级越多,热固结也越充分,其对应的体变、强度增长率则越大;同时最终温度及热固结路径对其剪切相转换特征存在影响,升温越高、热固结路径越多其剪胀性越明显,但温度变化范围、固结分级、热固结路径总体上对孔隙水压力的发展基本不产生影响。