兰州大学机构库 >土木工程与力学学院
纳米二氧化硅固化黄土力学性能和结构特征研究
Alternative TitleStudy on mechanical properties and structural characteristics of nano-SiO2 stabilized loess
孔冉
Thesis Advisor谌文武
2019-09-30
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name博士
Degree Discipline地质工程
Keyword黄土 纳米二氧化硅固化 力学性能 结构特征 机理分析 性能评价
Abstract黄土广泛分布在世界上的许多地方,而中国是世界上黄土分布最广泛的国家。由于黄土特殊的性质和结构特征,在加载和变湿过程中常易发生变形破坏,形成了大量的滑坡等地质灾害、水土流失等环境灾害、沉降等工程问题,已造成了大量的经济损失和人员伤亡。加之当前黄土高原大规模的平山造地等人类工程活动,必将加剧对黄土性质和行为的改造,形成更多不可预测的工程问题和灾害事件。可见,黄土既是一种常见的灾害材料,又是一种典型的问题性土。因此,采用环境友好的固化方法提升黄土性能,分析固化黄土性能提升的规律,解释固化黄土性能提升的机理,对保障黄土工程中的安全运营和生命周期具有重要的经济社会价值,为黄土高原中水土流失和地质灾害提供新的解决方案,也具有实际的工程意义。本研究选择了甘肃省兰州市马兰黄土为固化对象,纳米二氧化硅为固化添加剂。首先,以0.0 %、0.2 %、0.4 %、0.8 %、1.0 %、1.5 %和2.0 %的质量比添加干的纳米二氧化硅到干黄土中;然后根据设计的含水量和干密度制作成标准的圆柱形试样,并对不同纳米二氧化硅添加含量的试样分别养护7天、14天、28天和60天;接着,利用无侧限单轴抗压强度评价了部分试样制备的质量,并对所有养护完成后的试样进行了密度和含水量等物理性质与抗压和抗拉力学性质的测试;随后,对养护后的试样进行了微观的XRD矿物成分、SEM微观电镜、BET孔径分布,细观颗粒尺寸分布、宏观结构崩解特性的测试分析;最后,分析纳米二氧化硅固化黄土力学性能提升的机理,评价了固化黄土状态结构、力学性能、结构稳定性和环境效应等方面的效果。从试样制备的相似度、试样制备的均匀性、人员制样的差异性3个方面的试样质量评价的结果发现,全自动电子伺服压力机上执行的无侧限单轴抗压强度测试是一种快速便捷的试样制备质量的评价方法,试样制备时的压制方向与测试时的加载方向会影响测试结果的一致性,不同研究人员在制备试样过程中引起的内部结构的细微变化会降低应力-应变关系曲线的吻合度。物理力学性能的测试结果和分析发现,在不同含量和养护周期下纳米二氧化硅固化黄土的基本物理状态均发生了不同程度的变化,固化黄土的含水量和密度均随养护周期的增长而降低,孔隙比只有非常轻微地增加,导致养护后固化黄土呈现了轻微地疏松化,而这些物理状态指标随含量的增加只有较小的变化;对于纳米二氧化硅固化黄土的力学性能而言,无侧限单轴抗压强度、割线模量、弹性模量、劈裂抗拉强度均随着含量的增加和养护周期的增长而增大,而纳米二氧化硅含量0.2 %固化黄土在较长养护周期下的力学性能也有明显的提升;力学性能各指标之间有很好的相关性,而与物理状态之间的关系相对较差;这些数据和结果均表明,纳米二氧化硅固化黄土物理力学性能的变化对养护周期的依赖性更强。纳米二氧化硅固化黄土结构特征的分析发现,在不同含量和养护周期下,纳米二氧化硅固化黄土没有发生化学上的反应,也没有产生可观察的新矿物成分;微细观尺度的数据显示,纳米二氧化硅添加到黄土以后,以填充固化黄土聚粒内的孔隙为主,形成了更加接触紧密和尺寸更大的聚粒,导致了聚粒间更大的微观孔隙尺寸,使固化黄土具有更大的累积总孔隙;浸水崩解过程不但反映了宏观的基本物理状态的调整,还很好地反映了试样聚粒状态和微观结构的变化。这些在微观、细观和宏观尺度上的结构特征很好地印证了宏观物理力学性质的变化。纳米二氧化硅固化黄土的机理分析和性能评价发现,纳米二氧化硅添加到黄土后发生的养护失水、结构聚集化和分散均质化效应是修改基本物理状态和提升力学性能的关键;新构建的养护含水量与平均颗粒尺寸比、养护含水量与累积孔隙体积比与传统的养护后含水量与纳米二氧化硅含量的水灰比相比,与固化黄土的力学性能存在更好的关系,表明了固化黄土性能与结构之间的紧密联系;性能评价结果显示,固化黄土的力学性能与结构稳定性均有明显地提升,且没有产生明显的化学环境效应变化。因此,纳米二氧化硅固化黄土性能提升本质上具有物理均质化与化学稳定性的固化机理。从以上的结论可以总结,纳米二氧化硅固化黄土的力学性能和结构特征的变化主要是物理修改的固化过程,宏观性能与微观结构之间存在紧密的联系,在没有化学环境效应发生下,固化黄土的力学性能和结构稳定性得到了显著地提升。可见,纳米二氧化硅可以作为一种潜在的环境友好的新材料去固化黄土。
Other AbstractLoess widely distributed in many parts of the world. China owns the largest loess deposit. Due to its special properties and structures during loading and wetting, here has encountered many geotechnical problems, geohazards, and environmental problems, such as landslide, erosion, and settlement in loess. These have caused serious injuries and significant economic losses. In addition, there are a lot of development projects to create land by filling valleys with soils cut from hilltops in the Chinese Loess Plateau. This may aggravate to modify the properties and behaviors of loess, which will lead to more unpredictable geohazards and engineering problems. So, loess is not only common hazard material but also typically problematic soil. Hence, there is a great need to improve loess performance using eco-friendly stabilized methods, then to analyze the changes of stabilized loess properties and its mechanism. It is important to socio-economic value to security and life cycle in loess engineering. It is also curial afford new solution to soil erosion and geohazards in the loess plateau.In this study, the samples were taken from Malan loess in Lanzhou city, Gansu province, and Nano-SiO2 is selected as the stabilized agent. First, the dry nano-SiO2 was added to the dry loess with a weight ratio of 0.0%, 0.2%, 0.4%, 0.8%, 1.0%, 1.5% and 2.0%. The cylindrical samples were prepared according to the designed water content and dry density. Then the samples with different nano-SiO2 contents were cured for 7, 14, 28 and 60 days, respectively. First, the unconfined compressive strength test was used to evaluate the sample quality during preparation. Then, the physical properties, unconfined compressive strength compressive and tensile strength of all samples were tested after curing. After that, the samples were tested and analyzed through XRD, SEM, BET, particle size distribution, and disintegration tests. Finally, the improved mechanism of mechanical properties of loess stabilized by nano-SiO2 was analyzed to assess the physical states, mechanical properties, structural stabilities and environmental effects of stabilized loess.This study evaluated their quality to sample similarity, sample uniformity, sample preparation of different researchers. The results found that the unconfined compressive strength test is a rapid and convenient method for sample preparation. The pressing direction of sample preparation and the direction of during loading can influence the consistency of the test results, and the samples prepared by different researchers can change the stress-strain curves.  The results from physical and mechanical tests found that nano-SiO2 stabilized loess has lower water content and density with increasing curing days. The void ratio shows a very slight increase, which results in a looser packing. And the physical index shows a small change with the increase of the nano-SiO2 content; The unconfined uniaxial compressive strength, secant modulus, elastic modulus, tensile splitting strength increased with increasing nano-SiO2 content and curing days. However, the loess stabilized by 0.2% of nano-SiO2 content has also obvious improvement in mechanical performance. There is a good correlation between mechanical properties. Nevertheless, there has a low relationship between mechanical properties and physical index. These results show that the physical and mechanical properties of the stabilized loess are more dependent on curing days.The results from structure characteristics showed that there not only has no chemical reaction in the stabilized loess with different nano-SiO2 contents and curing days, but also no new mineral components. The microscopic results showed that the intra-aggregate pore will be filled by nano-SiO2, forming tighter contact and greater aggregate. Consequentially, there has greater inter-aggregate pore. The disintegration tests not only reveal the changes in the macroscopic properties, but also the adjustment of the aggregates and its microstructures. The physical and mechanical properties of stabilized loess can be confirmed by micro-, meso- and macro-structure characteristics.  The results from mechanical analysis and performance assessment found that the mechanics includes the loss of water during curing, structure aggregation, and dispersion homogenization. It is key to the modification of physical properties and the improvement of mechanical properties. Compared the traditional water-additive ratio with the ratio of post-curing water content and nano-SiO2 content, the newly parameters: both the ratio of water content after curing and average particle size and the ratio of water content after curing and cumulative pore volume ratio have a better relationship with the mechanical properties of cured loess, indicating a close relationship between the properties and structure of cured loess. The results of performance evaluation show that the mechanical properties and structural stability of cured loess are improved obviously, and there is no noticeable change in the chemical environment effect. Hence, the performance improvement loess treated by nano-SiO2 have the characteristic of physical homogenization and chemical stability in the stabilized mechanism.From the results above, it can be concluded that the mechanical properties and structural characteristics of loess stabilized by nano-SiO2 are mainly the processes of physical modification. There is a close relationship between the macroscopic properties and microstructures, and the mechanical properties and structural stability are significantly improved without chemical activity. Therefore, nano-SiO2 can be used as a potential eco-friendly new material to stabilize loess.
Pages114
URL查看原文
Language中文
Document Type学位论文
Identifierhttp://ir.lzu.edu.cn/handle/262010/342385
Collection土木工程与力学学院
Affiliation土木工程与力学学院
First Author AffilicationSchool of Civil Engineering and Mechanics
Recommended Citation
GB/T 7714
孔冉. 纳米二氧化硅固化黄土力学性能和结构特征研究[D]. 兰州. 兰州大学,2019.
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