【作者】 张平；

【导师】 房营光；

【作者基本信息】 华南理工大学 ， 岩土工程， 2011， 硕士

【摘要】 软土是工程建设中常见的天然地质材料,广泛分布于沿海、河流中下游及湖泊的三角洲地区,其物理力学性质非常复杂,具有含水量高、孔隙比大、压缩性高、强度低、渗透性差、结构性和流变性显著等特点,其中具有代表性的淤泥和淤泥质土,主要由极细的粘土颗粒、有机物、氧化物等固相物质和水组成。长期以来,人们主要从宏观层次研究软土的工程特性,唯像地解释软土不良的工程性质,难于揭示产生不良工程特性的物理机制和本质规律。本文通过实验,测试细颗粒软土固结过程的孔隙率、孔隙尺度分布等孔隙特征及其变化规律,分析软土固结特性的微观机理及其变化机制,为软土地基加固设计提供有价值的理论参考。本文开展的主要研究工作和取得的成果有如下几个方面:(1)综述了土体微结构测试技术的若干进展,介绍了土体微结构的常用测试方法,包括压汞法、气体吸附法、扫描电子显微镜分析法和CT法等。(2)试样制备方法研究。文中对不同的试样制备方法,包括风干法、烘干法和冻干法对软土孔隙特征试验的影响进行研究分析。研究表明,不同的试样制备方法对土体孔隙分布存在一定的影响,且试样的的含水率越高,影响越明显;风干法和烘干法制作试样会引起孔隙收缩,导致土体微孔隙特征的改变;而冻干法不引起孔隙收缩,对土体微孔隙特征的影响很小。因此,冻干法是制备测试软土孔隙特征试样的最佳方法,这一研究结果对土体孔隙特征测试的实验有重要指导作用。(3)天然软土的孔隙特征测试。分别对深圳软土、南沙软土和珠海软土进行了孔隙特征测试。从压汞试验测得的累积进汞量曲线,求得了各土样的退汞效率、总孔面积、平均孔径和曲折因子。试验结果表明,天然软土的孔隙主要分布范围是40nm～2.5μm,占土中总孔隙的80%以上,其中直径为500~1100nm的小孔隙占主要部分。(4)重塑软土的孔隙特征测试。分别对重塑深圳软土、重塑南沙软土和重塑珠海软土进行了孔隙特征测试。从压汞试验测得的累积进汞量曲线,求得了各土样的退汞效率、总孔面积、平均孔径和曲折因子。试验结果表明,重塑深圳软土的孔隙主要分布范围是40nm～2.5μm和10μm～34.4μm,占土中总孔隙的85.8%,其中直径为183nm的微孔隙占主要部分,重塑南沙软土和重塑珠海软土的孔隙主要分布范围是40nm～2.5μm,分别占土中总孔隙的52.8%和82.9%,其中重塑南沙软土直径为3187nm的小孔隙占主要部分,重塑珠海软土直径为1621nm的小孔隙占主要部分。将土重塑以后,土中大孔隙和中孔隙的含量明显增大,小孔隙的含量明显减小,微孔隙和超微孔隙的含量基本不变,同时软土经过重塑以后,渗透系数急剧增大。重塑软土中大孔隙和中孔隙的含量增大是土的渗透系数急剧增大的主要原因。(5)研究了掺加不同比例的膨润土的细颗粒土的微孔隙特征。试验结果表明,只要加入少量的膨润土便可使土体中大孔隙的数量急剧减少;随着膨润土的含量的增多,孔隙尺度分布逐渐发生变化,中孔隙的数量逐渐减少,小孔隙、微孔隙和超微孔隙的数量逐渐增多,峰值所对应的孔隙直径减小。在高岭土中加入不同比例的膨润土后,土的孔隙主要分布范围是40nm～2.5μm,占土中总孔隙的81%以上,其中直径为553~1313nm的小孔隙占主要部分。在石英中加入不同比例的膨润土后,土的孔隙主要分布范围是300nm～11μm,占土中总孔隙的78%以上,其中直径为1051~6037nm的小孔隙和中孔隙占主要部分。(6)不同荷载下固结的软土的孔隙特征测试。对于同一种土,孔隙比先随固结压力增大而显著降低,之后随着固结压力的增大,孔隙比缓慢减小,最后孔隙变化趋于稳定;随着固结压力的逐渐增大,曲折因子缓慢增大,平均孔径不断减小。对于重塑石英、深圳软土、南沙软土和珠海软土中的任何一种土样,随着固结压力的增加,较大尺度的孔隙(如大、中孔隙)的百分比有所减小,而小尺度孔隙(小、微、超微孔)的百分比则有所增加。上述结果说明,在压力作用下,较大尺度的孔隙被压碎分裂成较小尺度的孔隙。固结过程中较大孔隙先被压缩,较小的孔隙后被压缩。大尺度的孔隙向小尺度的孔隙转化,最终小尺度孔隙(小、微、超微孔)占据主导地位。更多还原

【Abstract】 Soft soil is a kind of common natural materials for civil engineering, which is widely distributed in coastal areas, middle-lower reaches of rivers and lacustrine delta areas. Slit and mucky soil are the most typical ones that characterized with complex physical-mechanical properties, such as high water content, large void ratio, high compressibility, low strength, weak permeability, remarkable structural and rheological properties and so on. Slit and mucky soil are mainly composed of solid phase matter including tiny clay particles, organics, oxides, and water. The research of engineering characteristics of soft soil is still focus on macroscopic stage mainly for a long time, which is unable to reveal the mechanism and essential law of its inferior properties. Base on experimental study, this dissertation analyzes :the pore diameter and pore-scale distribution after consolidation and seepage characteristics of tiny-particle soft soil.The outline of the research tasks and achievements of this dissertation are listed as follows:(1) Some advances of testing methods in microstructure of soil were reviewed in this paper, the methods in common use for testing microstructure of soil are introduced, which include the mercury method, the gas-adsorption method, the scanning electron microscopy analysis method and computerized tomography method.(2) Sample preparation methods research. Based on different sample preparation methods, including air dry method, drying method and freeze dry method on soft soil characteristics of the influence of porosity test research and analysis. Research shows that different samples of soil preparation methods have a certain influence on the pore distribution, and the higher the moisture content of the samples, the more obvious influence; air dry method and drying method legal system for sample can cause pore contractive, led to the changes of character of soil micro pore; And freeze dry method not cause pore contractive, the soil micro pore features a little effect. Therefore, freeze drying is soft soil preparation of test sample the best method of pore characteristic, the findings of the pore characteristic of soil testing experiment is important guiding role.(3) Pore characteristic test of natural soft soil. This paper test the pore characteristic of Shenzhen soft soil、Nansha soft soil and Zhuhai soft soil. Mercury injection measured from the accumulation of test into mercury quantity curve, the soil samples obtained the retreat mercury efficiency, total aperture area, average aperture and twists factor. Test results show that the main natural soft soil pore distribution is 40nm ~ 2.5 muon m, accounting for soil more than 80 percent of the total pore diameter, among them the small pore between 500 ~ 1100nm is main parts.(4) Pore characteristic test of remolded soft soil. This paper test the pore characteristic of remolded Shenzhen soft soil、remolded Nansha soft soil and remolded Zhuhai soft soil. Mercury injection measured from the accumulation of test into mercury quantity curve, the soil samples obtained the retreat mercury efficiency, total aperture area, average aperture and twists factor. Test results show that the main pore distribution of remolded Shenzhen soft soil is 40nm ~ 2.5 muon m and 10 muon m ~ 34.4 muon m, accounting for soil more than 85.8 percent of the total pore diameter, among them the micro pore of 183nm is main parts.,the main pore distribution of remolded Nansha soft soil and remolded Zhuhai soft soil is 40nm ~ 2.5 muon Clay accounted for the total porosity 52.8 and 82.9%, among them the small pore of 3187nm is main parts of remolded Nansha soft soil,and the small pore of 1621nm is main parts of remolded Zhuhai soft soil. After reshape the soil, big porosity and pore content increased obviously , Small pore content is reduced obviously, micro pore and superfine pore content basically unchanged. Meanwhile soft soil after remodeling , the permeability coefficient increases dramatically . In remolded soft soil, big porosity and pore content increased is the main reason for the sharp increase of permeability of soils.(5) Study the micropore structure characteristics of the soil added with different bentonite content.The test results show that just adding a little bentonite can reduce the quantity of the large pore abruptly. With the increase of bentonite content, the pore-scale distribution changes gradually, the quantity of the middle pore increases, the quantities of the small pore , the micro-pore and the supermicro-pore increase gradually,and the pore diameter size corresponding the peak decreases.After kaolin added with different bentonite content, the main soil pore distribution is 40nm ~ 2.5 muon m, accounting for soil more than 81 percent of the total pore diameter, among them the small pore between 553 ~ 1313nm is main parts. After quartz added with different bentonite content, the main soil pore distribution is 300nm ~ 11 muon m, accounting for soil more than 78 percent of the total pore diameter, among them the small pore porosity and pore between 1051 ~ 6037nm is main parts.(6) Under different load of soft soil consolidation of pore characteristic test. For the same soil, porosity ratio reduced significantly as consolidation pressure increase at first, then with the increase of consolidation pressure, porosity ratio decreases slowly,finally the pore change remained stable; along with the consolidation pressure increases gradually, twists factor increases slowly, average aperture constantly decreases. To remolded quartz, shenzhen soft soil, nansha soft soil and zhuhai soft soil in any one kind of soil samples, as consolidation pressure increase, the percentage of large scale pore (such as big pore,pore) reduced, and the percentage of small scale pore (small pore, micro pore, utrasmall pore) increased. The above results indicate that under the action of the pressure, large scale pore crushed split into smaller scale of porosity, finally small scale pore (small and micro, utrasmall hole) hold dominant position.更多还原