珠海软土固结性质的宏微观试验及机理分析

发布时间：2018-06-27 14:43

本文选题：珠海软土 + 固结性质　；参考：《华南理工大学》2013年博士论文

【摘要】：软土是工程建设中常见的天然材料，其物理力学性质非常复杂，具有高含水量、大孔隙比、高压缩性、低强度、且渗透性差、结构性显著等特点，广泛分布于沿海、河流中下游及湖泊的三角洲地区。在软土中具有代表性的有淤泥和淤泥质土，主要是由极细的粘土颗粒、有机物、氧化物等固相物质和水组成。珠海软土表现出典型的软土性质，其地基土呈现出低承载力、大沉降量、沉降稳定所需时间长等，这将会直接影响工程造价、进度以及安全性。大量的研究与实践证明，软土特定的历史环境会影响其工程性质的形成，而且软土的工程性质不仅与其矿物成分，颗粒大小、深度、外荷载状态及排水条件有关外，还与其微观颗粒及孔隙特征、颗粒的连结方式及组成排列、颗粒之间的胶结方式等微观结构形态特征有关。目前阶段而言，大量学者都主要从宏观层面对软土的工程特性进行研究，而这从根本上解释不了软土表现不良工程特性的本质规律。本文通过宏观与微观试验，系统的介绍了研究珠海软土工程性质的手段方法，分别从宏观及微观的角度分析了珠海软土固结等工程特性及其固结过程变化的微观机制。本文主要开展的研究工作以及理论成果如下：（1）通过珠海原状软土不同深度的室内基本物理力学性质试验，得出珠海软土颗粒土以细粒土为主，粘土矿物含量大。珠海软土中颗粒以粘粒和粉粒等细粒土为主，且矿物成分中，粘土矿物以高岭石为主，其次为伊利石，蒙脱石含量较少。比表面积较大，液塑限与其比表面积呈正相关关系；粘土矿物比表面积值及吸附性能强于非粘土矿物，结合水量高；比表面积与渗透系数呈现一定负相关性，表现出比表面积越大，渗透性越低的特征。（2）通过珠海软土的常规固结试验及回弹试验的成果数据，可以得出珠海软深厚土层属于欠固结土。软土的固结特征与先期固结压力相关，当固结压力超过先期固结压力时，土体的固结速率呈现增长趋势。水平向固结系数在固结的初始阶段与竖向固结有较大区别，随着土样深度的增加，最终的固结系数稳定值呈现减小趋势。珠海相软土的结构性较强，当固结压力超过上覆土体荷载时，土体处于回弹初始阶段，回弹曲线特征较为平缓；当固结压力卸载到小于上覆土体荷载时，土样处于快速回弹阶段，回弹曲线特征较陡，孔隙比增长迅速。（3）运用环境扫描电子显微镜技术对珠海原状不同深度及不同切面方向的软土以及固结后的土样进行观测分析，得出珠海天然软土的微观结构主要有蜂窝状结构、海绵状结构及凝块状结构三种类型。土颗粒呈曲片絮凝状叠聚体，微孔隙分布较多，深部比浅部土样的微观颗粒小，密实度大，且絮凝结构明显，微孔隙分布多，定向概率熵较大。固结过程中大量的大孔隙被压缩成小孔隙，土体变得更加密实，颗粒也无明显定向性，颗粒单元体呈现出由原来边-面、边-边组合转化为面-面组合为主，无明显曲片状结构，颗粒凝聚成团，且相互之间接触紧密。在荷载增加的过程中，孔隙中的水分减少，结合水膜变薄，颗粒凝聚成团状形式。大孔隙面积和数量减少，小孔隙数量增多，等效孔径相应减小，孔隙由粒间孔隙向团聚单元体内部孔隙转变。固结过程中垂直方向比水平方向的微观性质变化明显，长轴容易被切割破坏成小颗粒，土样的微观结构单元体特性主要在受压方向发生相应的变化。（4）通过压汞试验，研究珠海软土的渗透作用对其微观孔隙尺度分布的变化影响，及固结过程当中土样的微观孔隙变化规律进行分析。珠海原状软土的微观孔隙都主要分布400nm-2500nm及30nm-400nm。渗透后土样的微观孔隙有所增大，渗透力的作用带走了部分颗粒，且孔隙集中分布孔径大于原状样的峰值孔径值，同时软土的孔隙面积有所减小，，且对微观孔隙尺度的分布有均化的作用。在固结过程中土体较大的孔隙逐渐转变为较小孔隙。软土试样在固结压力100kPap200kPa时，孔隙比和平均孔径都减小迅速；而当固结压力p200kPa，孔隙比及平均孔径仍在减小，但速度减缓。（5）针对单向固结的普遍方程和太沙基单向固结理论，通过微观参量比表面积S、等效孔径D、颗粒的定向概率熵H m、颗粒的分形维数D p与土的固结系数的相应关系，给出了考虑微观因素修正的固结系数方程，并通过微观参量的范围取值，给出了相应微观参量的影响因子α、β、ζ、η数值。并通过实际的工程，真空联合堆载预压对珠海金湾软土的现场取样图片、十字板剪切数据、及实际固结沉降量等结果的分析，验证其分析值与室内的宏观与微观试验测试分析的数据及理论的正确性及可靠性。
[Abstract]:Soft soil is a common natural material in engineering construction, its physical and mechanical properties are very complex, with high water content, large pore ratio, high pressure shrinkage, low strength, poor permeability and significant structural characteristics, widely distributed in the coastal area, the middle and lower reaches of the river and the delta area of the lake. In the case of fine clay particles, organic matter, oxide and other solid substances and water, the soft soil in Zhuhai shows typical soft soil properties, and its foundation soil presents a low bearing capacity, large settlement, and a long settlement, which will directly affect the cost, progress and safety of the project. A large number of research and practice have proved that soft soil is specific. The historical environment will affect the formation of its engineering properties, and the engineering properties of the soft soil are not only related to its mineral composition, particle size, depth, external load state and drainage conditions, but also with the microscopic particle and pore characteristics, the connection mode and composition of particles, the cementation between particles and other microstructure features. In the previous stage, a large number of scholars mainly study the engineering characteristics of soft soil from the macro level, which can not fundamentally explain the essential law of the soft soil performance. This paper systematically introduces the methods and methods to study the engineering properties of Zhuhai soft soil through macroscopic and microscopic tests, respectively, from the macro and micro angles. The microstructural mechanism of consolidation and other engineering characteristics of soft soil in Zhuhai is analyzed.
The main research work and theoretical achievements in this paper are as follows:
(1) through the laboratory basic physical and mechanical properties test of different depth of Zhuhai soft soil, it is concluded that the soft clay in Zhuhai is mainly fine grained soil with large clay mineral content. The particles in Zhuhai soft soil are mainly fine clay particles such as clay particles and powder particles, and in the mineral composition, clay minerals are mainly high ridge, followed by illite, and the content of montmorillonite is less than that of illite. The surface area is larger, and the liquid plastic limit is positively related to the specific surface area; the clay mineral is stronger than the surface area and the adsorption property is stronger than the non clay mineral. The specific surface area and permeability coefficient show a certain negative correlation, which shows that the larger the surface area is, the lower the permeability is.
(2) through the data of conventional consolidation test and rebound test of Zhuhai soft soil, it can be concluded that soft deep soil in Zhuhai belongs to underconsolidated soil. The consolidation characteristics of soft soil are related to the pre consolidation pressure. When consolidation pressure exceeds the pre consolidation pressure, the consolidation rate of soil is increasing. The horizontal consolidation coefficient is in the initial order of consolidation. There is a great difference between the vertical consolidation and the vertical consolidation. With the increase of the soil sample depth, the final stability of the consolidation coefficient decreases. The structure of the Zhuhai phase soft soil is stronger. When the consolidation pressure exceeds the overlying soil load, the soil is in the initial stage of rebound, and the characteristic of the rebound curve is relatively gentle; when the consolidation pressure is less than the overburden soil load, the consolidation pressure is less than the overburden soil load. At the time of loading, the soil sample is in a rapid rebound stage, and the rebound curve is steeper and the void ratio increases rapidly.
(3) by observing and analyzing the soft soil with different depth and different tangent direction in Zhuhai with environmental scanning electron microscopy, it is found that the microstructure of Zhuhai natural soft soil mainly consists of honeycomb structure, spongy structure and three types of clot like structures. In the deep part, the depth is smaller than the shallow soil, the density is large, the flocculation structure is obvious, the distribution of the micropore is more and the directional probability entropy is larger. In the consolidation process, a large number of large pores are compressed into small pores, the soil becomes more dense and the particles have no obvious orientability, and the granular element body is transformed from the original side to side, side side combination transformation. In the process of the increase of load, the water in the pore is reduced, the water film becomes thinner and the particles are condensed into a mass form. The size and quantity of the macropores are reduced, the number of small pores increases, the equivalent pore size decreases, and the pores are from intergranular pores. The internal pore changes in the agglomeration unit. In the process of consolidation, the microscopic properties of the vertical direction change obviously than the horizontal direction. The long axis is easily cut into small particles, and the characteristics of the microstructural elements of the soil sample are mainly changed in the compression direction.
(4) through the mercury pressure test, the influence of the permeability of Zhuhai soft soil on the change of the micropore size distribution and the micropore change law of the soil samples during the consolidation process are analyzed. The micro pores of the original soft clay in Zhuhai are mainly distributed in the micro pores of 400nm-2500nm and 30nm-400nm. infiltration, and the permeability is increased. Some particles are taken away, and the pore size distribution is larger than the peak value of the original sample, while the pore size of the soft soil decreases, and the pore size distribution is homogenized. During the consolidation process, the larger pores of the soil gradually change to smaller pores. The pores of the soft soil specimen are at the consolidation pressure of 100kPap200kPa. The ratio and average pore diameter decrease rapidly, while the pore ratio and average pore diameter decrease while the consolidation pressure is p200kPa, but the speed decreases.
(5) in view of the universal equation of unidirectional consolidation and the unidirectional consolidation theory of Tai Sha foundation, the relation between the microscopic parameter specific surface area S, the equivalent aperture D, the directional probability entropy H m of the particle, the fractal dimension D P of the particle and the consolidation coefficient of the soil is given, and the equation of the fixing coefficient considering the correction of the microcosmic factors is given, and the value of the microscopic parameters is obtained. The results of field sampling pictures, cross plate shear data and actual consolidation settlement of Zhuhai Golden Bay soft soil were analyzed by the actual engineering, vacuum combined loading preloading, and the data and theory of the analysis value of the analysis value and the macro and micro test test in the room were verified. Correctness and reliability.
【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU447

【参考文献】