粉煤灰改性分散性土的工程特性及其机制研究

发布时间：2018-04-11 09:22

本文选题：分散性土 + 粉煤灰　；参考：《西北农林科技大学》2017年硕士论文

【摘要】：分散性土是近年来岩土工程领域较为关注的特殊土类之一,其具有抗冲蚀能力低、破坏过程迅速、隐蔽的特点,对处于分散性土地区的水利工程等产生极大的危害。粉煤灰作为燃煤火电厂的次生产物,本身具有一定的活性和黏聚力,并且具有压缩性小、强度高、水稳性强等工程特点,因此可作为土体的改性材料。本文基于黏性土体的分散机理,采用针孔试验、碎块试验、压缩试验、无侧限抗压强度试验、自身抗渗试验、扫描电镜试验以及压汞试验等方法,研究了粉煤灰对分散性土的分散性、压缩性、强度特性、抗渗性能以及微观结构的影响,并对粉煤灰改性分散性土的机制进行了分析。研究结论如下。(1)粉煤灰对分散性土的分散性具有良好的改性效果,影响因素主要包括粉煤灰剂量、养护龄期和压实度。随着粉煤灰剂量的增加,养护龄期的延长,压实度的提高,分散性土逐渐丧失分散性,先呈现过渡性土的特征,进而转变为非分散性土。建议在实际工程中,粉煤灰剂量大于4%,养护7d以上,压实度控制在96%以上。(2)粉煤灰可有效降低土体的压缩变形,提高土体的强度及抗渗性能。在同一养护龄期下,随着粉煤灰剂量和养护龄期的增加,土体的压缩性均逐渐降低,无侧限抗压强度逐渐增大。养护7d后,土体的压缩性基本处于一种稳定状态。养护初期,粉煤灰剂量对土体的无侧限抗压强度几乎没有影响。在分散性土中掺入粉煤灰后,土体的渗透破坏坡降逐渐增大,土体的抗渗性能显著增强,可提高土体的渗透稳定性。(3)粉煤灰改性分散性土的主要机制包括水解水化反应、离子交换反应、硬凝反应等,通过这些反应,土体的压缩性明显降低,无侧限抗压强度以及抗渗性能显著提高。扫描电镜结果表明,粉煤灰与分散性土反应生成的水化产物逐渐增多,使得骨架颗粒之间的接触面积增大,骨架颗粒之间的接触方式由点接触转变为面接触,土体的密实性增加。压汞试验结果表明,颗粒之间的孔隙逐渐减小,直径在1~10μm的孔隙数量减小,0.1~1μm的孔隙数量增加。
[Abstract]:Dispersive soil is one of the special soils in geotechnical engineering field in recent years. It has the characteristics of low erosion resistance, rapid failure process and concealment, which has great harm to water conservancy projects in dispersed land areas.Fly ash, as the secondary product of coal-fired power plant, has certain activity and cohesion, and has the engineering characteristics of low compressibility, high strength and strong water stability, so it can be used as the modified material of soil.In this paper, based on the dispersion mechanism of clay soil, the methods of pinhole test, fragment test, compression test, unconfined compressive strength test, self impermeability test, scanning electron microscope test and mercury injection test are used.The influence of fly ash on dispersity, compressibility, strength, impermeability and microstructure of disperse soil was studied, and the mechanism of fly ash modified dispersible soil was analyzed.The results are as follows: (1) fly ash has a good effect on the dispersity of dispersible soil, and the influencing factors mainly include the dosage of fly ash, curing age and compaction.With the increase of the dosage of fly ash, the prolongation of curing age, the increase of compaction degree, the dispersive soil gradually loses its dispersity, and it first presents the characteristics of transitional soil and then changes into non-dispersive soil.It is suggested that in practical engineering, the dosage of fly ash is more than 4, the curing time is more than 7 days, and the compaction degree is more than 96%.) fly ash can effectively reduce the compression deformation of soil and improve the strength and impermeability of soil.Under the same curing age, with the increase of fly ash dosage and curing age, the compressibility of soil gradually decreases, and the unconfined compressive strength increases gradually.After 7 days of curing, the compressibility of soil is basically in a stable state.At the early stage of curing, the dosage of fly ash has little effect on the unconfined compressive strength of soil.After the addition of fly ash into dispersible soil, the slope of soil seepage failure gradually increases, and the impermeability of soil increases significantly, which can improve the permeability stability of soil. The main mechanism of fly ash modified dispersible soil includes hydrolysis and hydration reaction.Through these reactions, the compressibility of soil is obviously reduced, and the unconfined compressive strength and impermeability are improved significantly.The SEM results show that the hydration products produced by the reaction of fly ash with dispersible soil increase gradually, which makes the contact area between skeleton particles increase, and the contact mode between skeleton particles changes from point contact to surface contact.The compactness of soil is increased.The results of mercury injection test show that the porosity between particles decreases gradually, and the number of pores with diameter of 1 ~ 10 渭 m decreases by 0.1 渭 m.
【学位授予单位】：西北农林科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV223

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