【作者】 邵玉娴；

【导师】 施斌；

【作者基本信息】 南京大学 ， 地质工程， 2011， 博士

【摘要】 本文紧紧围绕粘性土工程性质的温度效应研究这一中心课题,以南京地区广泛分布的三种粘性土为研究对象,根据南京城区季节性温差和城市热岛效应实测温度数据,选择5-50℃作为本次研究的试验温度范围,对三种粘性土进行了一系列的温度效应试验研究,得到了三种粘性土吸附结合水量、液塑限、渗透性、膨胀性和强度与温度的变化关系,并对其工程性质温度效应的相关机理进行了分析,相关研究成果归纳如下：1.采用容重法对三种粘性土烘干试样在不同温度下的吸附结合水量进行了试验分析,结果表明：随着环境温度的升高,三种粘性土的吸附结合水量随温度升高呈线性减少,吸附结合水量随温度的变化率与上中亲水性矿物的含量成正比；升温过程可以加快结合水膜内水分子的热运动,使得扩散层中部分水分子挣脱粘土颗粒表面吸附力的作用,游离出吸附水膜成为自由水,导致吸附结合水含量减少。2.随着温度的升高,三种粘性土的塑限变化不大,但液限变化明显。对于不含有机质的粘性土,粘性土中部分结合水转化为自由水,使得粘性土的液限和塑性指数降低,且变化的幅度也与亲水矿物的含量有关；对于含有少量有机质的粘性土而言,升温过程则使有机质活化能增大,吸附能力增强导致液限有所升高。通过试验建立了三种粘性土的界限含水量与温度的关系,证明了结合水膜厚度随温度减小的结论。3同一干密度的三种粘性土的渗透系数都随温度升高呈线性增长趋势,渗透系数随温度的变化幅度呈下蜀土(S2)>淤泥质土(S1)>膨胀土(S3)；不同密度土样的渗透系数随温度的变化率不同,低密度土样的渗透系数变化率比高密度土样大；粘性土干密度越大,渗透系数越小；粘土颗粒结合水膜变薄,土中水的粘滞阻力降低是粘性土渗透性随温度升高而增大的主要原因：结合粘性土吸附结合水试验,发现土中水以何种形式存在以及其随温度的变化规律,直接影响到粘性土的渗透性。4.随着环境温度升高,三种土样的无荷膨胀率均呈线性增大趋势,但增长速率不同,初始膨胀率大的试样反而热膨胀率小。粘性土试样的热膨胀是多种因素共同作用的结果,一方面水和固体颗粒受热膨胀；另一方面,结合水膜厚度的变化是粘性土热膨胀性差异的重要原因。5.温度的变化对非饱和粘性土的强度有一定的影响。温度对粘性土的粘聚力的影响较大,而对内摩擦角的影响规律不明显；对于亲水矿物含量较低的粘性土,当含水量较低(w≤17%)时,表现为强度的热硬化现象,且含水量相同,干密度越高的试样,热硬化现象越明显;当含水量较高(w≥22%)时,表现为强度的热软化现象,此时干密度对粘聚力及其温度效应的影响不大；亲水矿物含量较高的粘性土粘聚力随着温度的升高而降低,表现为强度的热软化现象；粘性土中亲水矿物含量越高,粘性土的强度对温度变化越敏感；非饱和粘性土强度的热硬化和热软化的内在机理与结合水膜的厚度和水的粘滞性的变化有关,同时还受到土的矿物成分、饱和度、密实度等多方面的影响。6城市热岛效应环境中地温场的变化对粘性土工程性质的影响具有一定的隐蔽性,其影响是缓慢的和长期的。根据本文试验结果和南京城市热岛效应强度的实测数据,当浅层土体中年平均城市热岛效应强度为2.14℃时,如S3的吸附结合水量减少了0.66%,强度降低了0.85kPa；在极端城市热岛效应环境中,浅层土体中城市热岛效应最大强度为3.98℃时,S2的渗透系数增加了1.45×10-7cm/s,城市热岛效应对粘性土工程性质的影响是显著的,应引起高度重视由于时间和试验条件的限制,本文对于粘性土工程性质的温度效应研究仅仅是初步的,论文在最后就该研究课题的进一步工作进行了分析和展望。更多还原

【Abstract】 This thesis focuses on the temperature effect on engineering properties of clayey soils. Taking three types of clayey soils in Nanjing as test samples,5-50℃as the test temperature range that is determined by the urban seasonal temperature difference and urban heat island effect in Nanjing. a series of experimental studies have been done in the temperature effects on the engineering properties of three types of clayey soils, including their adsorbed water content, Atterberg limits, permeability, swelling properties and strength etc. and the related mechanisms of the temperature effect on engineering properties are analyzed and the corresponding findings are presented as follows:1. Adsorbed water content of three types of drying clayey soils were tested under various temperatures by unit-weight method. It showed that as the environmental temperature rose, adsorbed water content in the three types of clayey soils decreased linearly and the change rate was proportional to the hydrophilic mineral content. The heating process speeded up the thermal motions of water molecules in bond water. The water molecules in the diffusion layer break away from the adsorptive force and turn into free water, leading to a decrease in adsorbed water content.2. As the temperature rose, the plastic limit of three types of clayey soils hardly changed, but the liquid limit changed remarkably. In the clayey soils with no organic matter, some bond water transform into free water, causing the liquid limit and the plastic indexes’reduction, and the reducing rates depends on the hydrophilic mineral content. For the clayey soils containing a small amount of organic matter, the heating process make the organic matter activation energy increase and the adsorption ability enhance, which leads to the liquid limit increase. The relationship between the Atterberg limits and temperature is established through laboratory study, and the conclusion of decreasing of electric double layer thickness is proved.3. The permeability coefficients of three soils samples in the same dry density increased linearly with the rise in temperature and, the amplitude of variation showing Xiashu soil(S2)> Silt (Sl)> Bentonite(S3). The change rates of the permeability coefficients under the temperature rise differed among the densities of soil samples. The change rates of the infiltration coefficients of lower-density soil samples were higher than those of higher-density soil samples. The higher density of clayey soils, the lower infiltration coefficients was. The two primary causes of the increase in permeability are the attenuation of the electric double layer thickness and the decrease in water viscous resistance. Combined with the experiment on adsorbed water content, it is proved that the forms and thermal variations of water in soils directly affected the permeability of clayey soils.4. As the environment temperature rose, the non-load expansion rates of each sample linearly increased, but the growth rates were distinct. The samples with higher inflation rates had lower thermal expansion rates. Several factors cause the thermal expansion:on one hand, soil particles and water expanded during heating; on the other hand, the changes of electric double layer thickness was a major factor of the thermal inflation rates difference.5. The temperature changes influenced the strength of clayey soils. Temperature had great effects on the cohesive force and unobvious influence on internal friction angle. For clayey soils with lower content of hydrophilic minerals, when the moisture content was lower(w<17%), the shear strength showed the thermo-hardening phenomenon. However, the thermal-softening phenomenon was shown when the moisture content was higher(w>22%), and the temperature effect on shear strength was more obvious when the dry density of sample is higher. The cohesive force of clayey soils with higher content of hydrophilic mineral decreased with the temperature rose, showing thermal-softening on strength, and its strength was more sensitive to temperature change. Moreover, the mechanism of thermal hardening and softening of strength of unsaturated clayey soils relate to the change of the electric double layer thickness and viscous resistance of water, but also affected by soil mineral composition, saturation, density, and other aspects.6. The influence on the engineering properties of clayey soil caused by the environment geothermal field change in urban heat island environment is complex, slow and long-term. According to the test results and the measured data of Nanjing urban heat island effect intensity, when the annual average urban heat island effect intensity is 2.14℃, the adsorbed water content of S3 decrease 0.66%, the strength reduce 0.85kPa; when extreme urban heat island effect intensity is 3.98’C, the permeability coefficient of S2 even increase 1.45×10-1cm/s. The influence on engineering properties of clayey soils caused by UHI effect is remarkable, and it should be payed higher attention to.Due to limits in time and laboratory conditions, this thesis is merely preliminary for the temperature effect research on the engineering properties of clayey soils, and further work on this research topic is analyzed and predicted in the final part of the paper.更多还原