颗粒岩土介质热导率预测关联式及其演化机制

以多相-多孔颗粒岩土介质热导率为研究对象,首先聚焦岩土颗粒几何形状特征构建细观颗粒/孔隙尺度改进型固液气三相圆柱单元结构;其次采用集总参数热电模拟法建立单元结构热导率与固液气组分热导率和孔隙率、饱和度等结构参数间的关联;进一步以饱和度参数为纽带,通过土水特征曲线类比提出统一性土-水-导热特征曲线及其演化机制概念模型。研究结果表明:(1)基于多尺度研究均质化思想建立的颗粒岩土介质热导率预测关联式模型无经验常数,各参数均有明确的物理意义,且提高了与实验测试结果的吻合度(与砂土实验测试结果的差异性比值由1.58降低至1.27,通过线性修正可进一步缩小误差至3%~16%);(2)颗粒岩土介质孔隙水分布形式与物理作用机制影响热导率的变化,不同类型(细粒含量、胶结程度)岩土介质热导率随饱和度变化曲线可以认为是由特定S型函数曲线沿低/高饱和度水平移动的演化过程,该演化机制可以解释岩土介质热导率随饱和度增加呈现出的"凹"与"凸"形增长关系,是可以统一表征不同岩土介质热导率预测模型的有效工具。     

土的热导率

本文简要论述了土的热导率研究的重要性，介绍了土的热导率的测试方法及土的热导率的变化规律。     

砂土地震液化及其防治

针对砂土振动液化这一现象，分析了引起砂土液化的原因，介绍了防治砂土地震液化的方法以及处理液化地基的措施，从而提高砂土的抗液化能力，防止或减轻地震时对建筑物的破坏。     

砂土液化的防范措施

通过砂土液化机理、砂土液化影响因素等的论述，提出了防止砂土液化的一些措施。     

考虑状态相关的砂土非正交弹塑性本构模型

砂土的力学特性具有显著的状态相关性，主要体现为不同应力状态与密实状态下砂土的变形特性具有显著差异。合理的状态相关硬化规律与剪胀规律描述是反映砂土状态相关变形特性的基础。提出了能够有效描述砂土等向压缩规律与临界状态规律的微分表达式，并基于等向压缩硬化规律建立了状态相关因子ω，发展了砂土状态相关的硬化参数H，旨在合理确定塑性应变增量的大小；在利用非正交塑性流动法则确定塑性应变增量的方向的过程中，引入了状态变量ψ对分数阶次μ的影响，从而考虑了塑性应变增量方向的状态相关性，合理地描述了砂土的状态相关剪胀性。进一步，结合引入了状态变量的Hooke定律，确定了弹性应变增量，从而发展得出能够描述砂土状态相关特征的非正交弹塑性本构模型。通过合理预测Toyoura砂的常规三轴排水及不排水试验结果，验证了所建模型能够有效捕获砂土的状态相关力学特性。     

振冲法加固砂土地基的试验及应用

根据某厂振冲碎石桩加固液化砂土地基的工程实践及试验资料，对挤密碎石桩加固砂土地基的机理进行了探索，并通过分析，进一步证明该法对砂土地基的加固是卓有成效的．从振冲碎石桩加固砂土地基的加固原理和受力情况出发，扼要阐述了振冲碎石桩加固砂土地基的设计要点和施工工艺．     

突变理论在砂土液化分析中的应用

突变理论主要研究事物的突变及不连续性态，目前在井巷围岩位移的判定及利用坡脚隆起位移研究滑坡方面得到了应用。砂土在振动作用下，从稳定状态到液化，具有突变性。基于突变理论对砂土液化安全系数的分析，建立了基于砂土液化安全系数法的突变模型，并针对历史场地砂土进行了分析计算，其结果与抗液化剪应力法和现场液化情况较吻合，表明突变理论应用于砂土液化分析是有效、可行的。     

基于支持向量机的砂土地震液化判别模型

根据影响砂土地震液化的主要因素，建立了砂土地震液化的支持向量机判别模型。该模型通过有限的经验数据的学习，获得了砂土地震液化与其影响因素之间的非线性映射关系。运用所建立的模型对具体的场地进行了液化判别，其结果表明，利用支持向量机理论构建分类器能在一定可靠度条件下正确判别砂土地震液化。     

砂土振动蠕变与长期强度研究

本文通过对砂土变形的细观分析，讨论了砂土振动蠕变机理，提出了振动蠕变长期强度的概念，认为砂土的振动蠕变长期强度数值上等于其剪胀临界应力，其测试可用静力试验取代费时费力的长期振动蠕变试验，这一结论与试验结果基本一致。     

基于可拓学理论的砂土液化势综合评价研究

将可拓学理论引入到砂土液化势评价工作中，利用网络编程技术开发了基于Web平台的可拓综合评价系统，选取最关键的7个参数作为评价指标，建立了砂土液化势的可拓评价模型，从而找到了砂土液化势评价行之有效的新途径。     

A modified Kozeny–Carman equation for predicting saturated hydraulic conductivity of compacted bentonite in confined condition

Kozeny–Carman (KC) equation is a well-known relation between hydraulic conductivity and pore properties in porous material. The applications of KC equation to predicting saturated hydraulic conductivities of sands and non-expansive soils are well documented. However, KC equation is incapable of predicting saturated hydraulic conductivity of expansive soil (e.g. bentonite) well. Based on a new dual-pore system, this study modified KC equation for improving the prediction of saturated hydraulic conductivities of bentonites. In this study, an assumption that inter-layer space (micropore) has limited effect on fluid flow performance of compacted bentonite was adopted. The critical parameters including total porosity and total tortuosity in conventional KC equation were replaced by macroporosity and tortuosity of macropore, respectively. Macroporosity and microporosity were calculated by basal spacing of compacted bentonite, which was estimated by assuming that specific surface area is changeable during saturation process. A comprehensive comparison of bentonite's saturated hydraulic conductivity predictions, including modified KC equation proposed in this study, conventional KC equation, and prediction method based on diffuse double layer (DDL) theory, was carried out. It was found that the predicted saturated hydraulic conductivity of bentonites calculated using modified KC equation fitted the experimental data better than others to a certain extent.     

脆性岩石损伤与热传导特性的细观力学模型

 基于均匀化方法给出低孔隙率脆性岩石在热–力耦合荷载作用条件下的各向异性损伤模型和有效热传导特性模型。其中,损伤模型可考虑非等温条件下裂纹的法向压缩变形、刚度恢复以及裂纹的滑动剪胀特性,热传导特性模型可反映损伤过程中细观结构的演化以及裂纹形态、孔隙率和饱和度变化对岩石有效热传导特性的影响。讨论低孔隙率结晶岩裂纹形态和饱和度对其有效热传导特性的影响;采用瑞典Äspö闪长岩在三轴压缩条件下的应力–应变曲线验证损伤模型的有效性,并分析岩石在损伤演化过程中裂纹体积率、密度、形态、饱和度和有效热传导特性的演化规律。研究成果对于深部岩体的热–力耦合特性研究具有一定参考意义。     

A composite sphere assemblage model for porous oolitic rocks: Application to thermal conductivity

The present work is devoted to the determination of linear effective thermal conductivity of porous rocks characterized by an assemblage of grains (oolites) coated by a matrix. Two distinct classes of pores, i.e. micropores or intra oolitic pores (oolite porosity) and mesopores or inter oolitic pores (inter oolite porosity), are taken into account. The overall porosity is supposed to be connected and decomposed into oolite porosity and matrix porosity. Within the framework of Hashin composite sphere assemblage (CSA) models, a two-step homogenization method is developed. At the first homogenization step, pores are assembled into two layers by using self-consistent scheme (SCS). At the second step, the two porous layers constituting the oolites and the matrix are assembled by using generalized self-consistent scheme (GSCS) and referred to as three-phase model. Numerical results are presented for data representative of a porous oolitic limestone. It is shown that the influence of porosity on the overall thermal conductivity of such materials may be significant.     

高温后聚丙烯纤维混凝土热工参数试验研究

采用瞬态热源法对高温处理后不同纤维掺量和纤维长度的聚丙烯纤维混凝土 PFRC 的热工性能开展试验研究。结果表明：高温后PFRC 的表观密度、导热系数、导温系数和比热容均随受热温度升高逐渐减小;孔隙率随着温度升高而增大,聚丙烯纤维的掺量及长度对混凝土的表观密度和孔隙率无明显影响,说明混凝土水分流失和水化产物分解是导致其高温下质量降低和孔隙增大的主要原因;经历同一温度后聚丙烯纤维掺量越高,混凝土的导热系数和导温系数越小。     

Effect of sedimentary facies and geological properties on thermal conductivity of Pleistocene volcanic sediments in Tokyo,central Japan

When ground source heat pump systems are installed underground, an estimate of the thermal conductivity is required to determine the desired total length of the heat exchanger (U-tube). Many large cities in Asia are built on Quaternary sediments, but the thermal conductivity of these sediments is not well understood. To measure the thermal conductivity of Pleistocene volcanic sediments in Tokyo, Japan, we discuss methods of measuring thermal conductivity and factors influencing the thermal conductivity of volcanic sediment, which has low quartz content. The results obtained from experiments using a drill core, borehole data and artificial sediment samples are as follows: (1) values of thermal conductivity predicted using water content, porosity or sand content can be underestimated in volcanic sediment or sediments with large amounts of magnetic minerals; (2) magnetic minerals have a higher thermal conductivity than quartz, so there is a relationship between magnetic susceptibility and thermal conductivity: (3) comparison of thermal conductivity measurements performed using box- and needle-type probes showed that the values measured using the former are comparatively larger. This decrease in thermal conductivity is explained by formation of air-filled cracks when the needle penetrates the sediment, as air has a lower thermal conductivity than sediment.

     

不同孔洞形式多孔砖当量导热系数模拟分析

依据导热系数概念,对当量导热系数进行定义。通过热模拟有限元分析软件Fluent,研究模拟分析过程中的步骤与技巧,针对单一多孔砖进行热工性能的模拟,对比分析影响多孔砖孔洞形式的6大因素即孔型、矩形长宽比、孔排数、孔列数、孔洞排列方式、孔洞率,分析6种因素对多孔砖当量导热系数的作用情况及影响原理,结果表明,孔型的选取应采用矩形孔;进行孔洞优化设计应在规范容许范围内增大矩形孔的长宽比,同时宜适当增加多孔砖的孔排数或孔列数;孔洞排列应采用交错布置的方式,且保证矩形孔长边垂直热传递方向;应在规范容许条件下尽量增大多孔砖孔洞率,并且确保力学强度达到使用需求。     

垂直地埋管地源热泵膨润土基钻孔回填材料导热特性研究

实验通过对膨润土基回填材料的配比、干密度、孔隙率、含水率和环境温度等因素研究发现,膨润土基回填材料的导热性能主要是由骨料(石英砂)含量、干密度和孔隙程度共同决定的,环境温度对回填材料导热性影响较小。含水率应合理控制,适宜配比、正确回灌能有效提高导热性和地下热交换器的工作效率,工程收益率高。     

Fluent软件在页岩空心砖孔型结构优化中的运用

采用基于有限容积法的Fluent软件,对190mm×240mm×115mm烧结页岩空心砖进行了当量导热系数的三维数值模拟和计算。模拟中主要考虑孔型、孔的长宽比、孔的排列数、孔洞率4个因素。模拟结果表明:矩形孔的当量导热系数最小,并随着矩形孔长宽比的增加,当量导热系数逐渐减小;另外,随着孔排列数、孔洞率的增加,空心砖的当量导热系数逐渐减小。     

高温后钢纤维混凝土热学性能试验研究

为预测火灾条件下SFRC 构件内部温度场,对高温后SFRC 的表观密度、孔隙率、导热系数、导温系数和比热容等进行了试验研究,并对导热系数下降机理进行混凝土细观尺度的数值模拟分析。研究表明,SFRC 的表观密度、导热系数和比热容总体上均随受热温度的上升而下降;孔隙率随受热温度的升高而上升,其中约有1%~3%的孔隙率是由SFRC 内热开裂造成;细观尺度有限元模拟显示高温热开裂形成的裂缝热阻是引起导热系数下降的主要原因之一;砂浆与素混凝土导温系数随温度升高而降低,但SFRC 导温系数在300 ℃时出现拐点,呈上升趋势;相同受热温度下,随着钢纤维含量的增加,导热系数和导温系数均呈上升趋势。