重塑黄土论文：渗流条件下重塑黄土强度的变化规律试验研究

1、重塑黄土论文：渗流条件下重塑黄土强度的变化规律试验研究【中文摘要】渗流是黄土工程性质劣化的一个重要原因。当黄土作为防渗材料时,在长期渗流作用下,由于复杂的土-水相互作用将改变原来土体的物理力学性质,最终导致强度降低。因此,研究渗流条件下黄土的强度和化学成分等物理力学性质随着时间的增长缓慢变化的规律具有重要的工程意义。鉴于室内模拟的难度,目前的研究主要集中于土-水相互作用机理上,对于渗流条件下黄土长期强度的研究极少。本文结合国家自然科学基金项目“黄土工程性质劣化机理与构筑物寿命预测研究”,以杨凌地区Q3重塑黄土为研究对象,通过室内试验模拟自然状态下土坝等黄土构筑物所经历的长期渗流作用,研究了不同

2、pH值渗流溶液对土体短期强度的影响以及酸性溶液较长时间渗流作用下土体中碳酸钙含量与抗剪强度之间的关系。土-水相互作用中主要有三种具有力学效应的化学作用即:溶蚀作用、沉淀或结晶作用和阳离子交换吸附作用。这三种作用发生的条件以及程度都受到土颗粒间水环境的影响。所以在不同pH值渗流溶液环境下,土体的短期强度也必然发生不同的变化。试验研究发现:经过酸溶液渗流后土体的强度比用纯水渗流之后的强度高,甚至会超过土样的初始抗剪强度。酸性溶液渗流条件下,土中矿物成分在酸性环境中发生一系列化学反应,主要是HCO 3-易溶盐在酸性环境下反应生成CO2气体,对土体强度在一定程度上起到了正面作用;渗流作用下,以碳酸钙为

3、主的胶结物以及其他盐分发生溶蚀和沉淀或结晶作用,改变了土颗粒的联结方式,阳离子交换吸附作用则改变土颗粒表面的双电层。这一系列复杂的反应使土样粘聚力c发生了不同程度的增大,而使内摩擦角发生了减小;在短期（10h）内,土体中碳酸钙含量和强度之间没有较强的相关性。这说明渗流初期土体中的物理化学作用比较剧烈,土中碳酸钙的溶蚀作用不能主导土体的抗剪强度变化。而经过较长时间的渗流之后,土体中难溶盐碳酸钙的溶蚀将对土体强度的变化起决定作用。在酸性溶液较长时间的渗流作用下,土-水相互作用持续发生。试验结果表明:此种情况下,由于碳酸钙的溶蚀流失,土体强度的时程曲线将会呈现出波浪起伏的形态。在分析其影响机理的基础

4、上,可以推断在一定时间内土体强度时程曲线的波动幅度将逐渐减小,峰值强度也持续降低。对比发现:低压实度土体对外部附加荷载（400kPa围压内）的反映相对迟钝,具体表现为土体强度时程曲线在各围压情况下呈现良好的一致性;而高压实度土体对外部附加荷载比较敏感,表现在不同围压情况下强度时程曲线都有差别,尤其是在低围压（200kPa）时。本文根据试验结果模拟土体中碳酸钙含量与强度（主应力差）相对变化率之间的关系,并建立了简单的数学模型,这也是本次研究的一个创新点。但是其准确性以及模型参数的物理意义、获取方法等还需要进行后续试验研究。【英文摘要】Seepage is an important reason

5、for the engineering properties deterioration of loess. The loessial physical and mechanical properties change with complex soil-water interactions carrying on under sustained seepage, which decreases its strength, when it is used as impermeable material. Therefore, it has important engineering signi

6、ficance to study on the law of loessial physical and mechanical properties （strength, chemical constituents, and so on） changing slowly with time-lapse. In view of the difficulty of laboratory simulation, the current researchs are concentrated on the mechanism of soil-water interactions, and little

7、on the loessial long-term strength under seepage. This paper studies on its short-term strength under seepage of different pH solutions and the relationship between its CaCO3 content and strength under sustained seepage of acidic solution by laboratory simulation, using Q3 remolded loess in Yangling

8、 as research object. It relies on the National Natural Science Foundation project“The Research of Properties Deterioration Mechanism of Loess Engineering and Life Prediction of Loess Structures”.It includes three chemical interactions with mechanical effect in soil-water interactions: dissolution, p

9、recipitation or crystallization, cation exchange adsorption. The water environment between soil particles affect on their occurrence and development. So the short-time strength of loess is different under seepage of different pH solutions. It is found through test that: The strength of loess after s

10、eepage of acidic solution is bigger than after seepage of pure water, even more than its initial strength. A series of chemical reaction take place between the bicarbonate in soil and acid under seepage of acidic solution, which produced carbon dioxide gas to increase the strength of loess; The diss

11、olution and precipitation or crystallization of calcareous cement and other soil salinity changed the connection between soil particles, and the cation exchange adsorption changed electric double layer on particle surface. This improved the cohesion while decreased the internal friction angle. It sh

12、ows a weak correlation between its CaCO3 content and strength in 10h. This suggests that the dissolution of CaCO3 is not the dominant factor of loess strength in the early seepage, but it could determine loess strength after long-time seepage. Soil-water interactions are continuous under long-time s

13、eepage of acidic solution. The results show that: The time-history curves present wave shape. Based on mechanism analysis, it can be deduced that the peak strength and fluctuation range of the time-history curves will decreased gradually. Comparison study shows that the remolded loess with lower com

14、pactness responded badly to external additional load （confining pressures lower than 400kPa）, while the time-history curves present strong consistency; But the remolded loess with higher compactness make good respond to external additional load, while the time-history curves are different under diff

15、erent confining pressures, especially lower confining pressures （200kPa）.This paper simulated the correlation between CaCO3 content and the relative change rate of loess strength and builds a simple mathematical model, based on the test results. It is an innovative point of this research. But it nee

16、ds more work to verify its accuracy, to determine the physical significance and acquisition method of the model.【关键词】重塑黄土 长期渗流 强度 碳酸钙含量【英文关键词】remolded loess sustained seepage strength CaCO3 content【目录】渗流条件下重塑黄土强度的变化规律试验研究摘要5-7ABSTRACT7-8第一章 绪论11-261.1 引言111.2 饱和粘性土的渗透特性11-181.2.1 粘性土孔隙水的分类11-121.2.2

17、 粘性土中孔隙水的渗流特性121.2.3 饱和粘性土的渗透特性12-151.2.4 饱和粘性土渗透特性研究现状15-161.2.5 长期渗流的研究现状16-181.3 水-土化学作用机理研究18-241.3.1 水-土化学作用机理19-201.3.2 水-土化学作用研究进展20-221.3.3 酸碱环境下水-土化学作用研究22-241.4 研究目的及内容24-261.4.1 研究目的241.4.2 研究内容24-26第二章 试验原理及方法26-322.1 试验原理26-272.2 试验方法27-322.2.1 渗流水溶液配制27-282.2.2 试验材料及试样制备28-302.2.3 试验内容30-32第三章 不同 pH 值溶液渗流对重塑黄土强度的影响研究32-423.1 引言323.2 重塑黄土抗剪强度及其指标的获取方法32-343.3 不同pH 值溶液渗流对重塑黄土抗剪强度的影响34-373.3.1 不同pH 值溶液渗流对土样主应力差的影响34-363.3.2 不同pH 值溶液渗流对土样c、值的影响36-373.4 渗流对重塑黄土强度及c、值的影响37-383.5 碳酸钙含量对重塑黄土