【作者】 付伟；

【导师】 汪稔；

【作者基本信息】 中国科学院研究生院（武汉岩土力学研究所） ， 岩土工程， 2009， 博士

【摘要】 随着我国寒区工程建设项目的增多，冻土的强度与变形问题以及冻胀融沉特性研究成为面临的最重要任务，但是由于冻土的复杂性，现有的冻胀机理相关研究尚不成熟，大多还是研究已冻土和融土物理力学性质差别，缺乏对正冻正融过程的相关研究。本文得到冻土工程国家重点试验室开放基金“冻土冻融过程的细观变形机理和结构性模型研究”的资助，针对青藏铁路北麓河粉质粘土，利用自主研发的电阻率测试设备，结合冻土单轴压缩试验设备和冻融循环试验设备，通过室内单轴压缩试验，系统的研究了单轴载荷下冻土电阻率的变化规律以及电阻率与力学指标间的关系；通过冻融循环过程电阻率试验，对正冻正融土体电阻率特性展开了初步研究。本文所研究内容及获得的结论主要包括以下几个方面：(1)分别用不同电源类型(直流电压、交流电源)、不同电路组成(伏安法、参比电阻法)在不同电压下进行试验，最终确定用10V直流稳压电源伏安法电阻测试方法能满足冻土电阻测试要求，并且通过试验获得了电极与土体间的接触电阻，并提出了真实电阻的修正方法。(2)通过不同干密度、不同含水量、不同温度冻土单轴载荷下电阻率-应力-应变试验研究表明单轴载荷下冻土经历压密、弹性变形、塑性屈服、破裂后四个阶段，诸阶段对应着电阻率变化趋势是减小至最小、电阻率平衡阶段、稳定增加、剧烈增加，并从细观角度上解释了四个阶段的应力应变电阻率机制。研究了冻土温度、干密度及含水量对电阻率的影响规律，建立了电阻率与单轴抗压强度的关系。(3)开展了封闭系统、开放系统下冻融过程电阻率试验，分析了封闭系统与开放系统下电阻率特性的异同性；分别针对冻融循环过程中土体的变形的五个阶段：冷缩、冻结剧增、冻胀稳定发展、融化骤减、完全融化后变形稳定阶段，进行电阻率变化机理研究。(4)通过饱和粉质粘土封闭系统下反复冻融过程电阻率试验表明：每次冻融中冻土电阻率随着冻融次数增加呈指数关系减小，融土电阻率随冻融次数增加呈指数关系增加；每次冻胀量与融沉量随冻融次数的增加而减小，平均干密度随冻融次数增加而增加，并且经过5次冻融循环后冻胀融沉量和干密度均趋于稳定。(5)通过单轴载荷与冻融作用下冻土电阻率特性试验研究表明土体电阻率与应力-应变关系、正冻正融过程以及土体温度的变化具有很好的同步性，说明利用电阻率实时观测的方法研究冻融循环过程、冻融作用对土体结构影响以及载荷作用下土体强度与变形问题是可行的。更多还原

【Abstract】 In China,more and more constructions in cold regions appear,Strength and deformationof frozen soil,characteristics of frost heave and thaw collapse have become the major task forcold regional construction.But researches on mechanism of frost heaving are still not maturedowing to complexity of frozen soil,and the current study,thinking little of the freezing andthawing process,mostly focuses on the different physical and mechanical properties betweenfrozen soil and thawed soil.It is funded by“research on the submacroscopic deformation mechanism and structuralcharacteristics of silty clay under freeze-thaw cycles”(an open fund of State Key Laboratoryof Frozen Soil Engineering).Using uniaxial compression and freeze-thaw cycle apparatuscombined with electrical resistivity observation for whole process,tests are performed for thesilty clay in Beilu River.Based on the experimental results,changes of electrical resistivity offrozen silty clay under uniaxial compression as well as the relationship between resistivityand mechanical properties have been studied systemically,and an Preliminary study onresistivity characteristics has been carried out for freezing and thawing soil.The main resultsof this paper are in detail listed in the following:(1)Orthogonal tests have been performed under different types of power(DC voltage,AC power),different circuit(voltammetry,reference resistor method)and different testvoltages.Through these experiments,the author introduces a new practical device forlaboratory measurement of frozen soil electrical resistivity,which uses two electrodes,10VDC regulated power and voltammetry circuit.Contact resistance between soil sample andelectrodes is obtained,and modified method of real resistance is proposed.Pilot test resultsshow that the equipment is effect and feasible in measuring electrical resistivity of frozen soil.(2)The test results under different dry density,water content and different temperatureshow that stress-strain curve can be separated into compression stage,elastic stage,plasticflow stage,break-up stage corresponding to decreasing fast stage,decreasing to minimumstage,steady increasing stage,unsteady increasing stage in resistivity-strain curve,themechanism of soil conductivity in every stage has been explained separately.The relationshipbetween resistivity and uniaxial strength is established.(3)This paper analyzes on the similarities and differences of resistivity characteristicsunder freeze-thaw cycle in closed system and in open system.The deformation in wholeprocess of freeze-thaw cycle can be divided into five stages:Cold-contraction,Dramaticincreasing,steady increasing,Dramatic decreasing owing to thawing,stability stage after complete thawing.The author analyzes electrical resistivity properties in differentdeformation stage separately.(4)The resistivity of saturated silty clay in closed system under repeated freeze-thawcycles is studied.The resistivity of frozen soil decreases and that of thawed soil increasesexponentially with increasing of freezing-thawing times.The amount of frost heave,thawcollapse and average dry density in every freeze-thaw cycle rise with increasing offreezing-thawing times,and they are trend to stability after 5 freeze-thaw cycles.(5)Researches show that changes of resistivity,temperature,pressure and deformationduring freezing-thawing cycles are real-time and synchronical,which proves that it is feasibleto study the changes of soil structure during freezing-thawing and problem of strength-deformation under external load by using electrical resistivity method.更多还原