pH值对云南红黏土力学特性及微观结构的影响

为探明土体在酸碱污染情况下力学特性和微观结构的演化规律,以云南红黏土为研究对象,以不同浓度的盐酸(HCl)和氢氧化钠(NaOH)为污染源,考虑酸碱全范围pH值变化和作用时间对红黏土抗剪强度的影响,并采用扫描电子显微镜(SEM)观察红黏土微观结构的变化。结果表明:与经历pH值为8.2的溶液处理过的红黏土相比,随着pH值升高或降低,红黏土的抗剪强度τ_f、黏聚力c、内摩擦角均呈现下降趋势;当pH值为0.5和13.8时,随着酸碱作用时间延长,红黏土的抗剪强度τ_f、黏聚力c、内摩擦角逐渐减小,7 d之后趋于稳定;对酸碱污染红黏土的SEM照片及其特征参数进行分析,发现酸碱污染红黏土抗剪强度衰减是酸碱溶液侵蚀土体结构导致的;碱污染红黏土与酸污染红黏土相比较,前者工程性质更差。该研究成果对云南红土地区水环境恶化型工程病险的认识和防治具有指导意义。

Effect of pH Value on Mechanical Properties and Microstructure of Yunnan Laterite

In order to explore the evolution law of mechanical properties and microstructure of soil under acid and alkali pollution, the Yunnan laterite polluted by different concentrations of hydrochloric acid (HCl) and sodium hydroxide (NaOH) was investigated. Then, the effects of full range of pH values and their action duration time on the shear strength of the Yunnan laterite were studied. The microstructure changes were detected by scanning electron microscopy (SEM). The test results show that the shear strength (τ_f) and the strength parameters (cohesion (c) and internal friction angle ()) all decrease with the decrease or increase of pH values compared with pH=8.2. The τ_f, c and  all decrease with extension of action duration time and come into stable after 7 d. SEM images and characteristic parameters of laterite polluted by acid and alkali were analyzed. The results show that the degradation of shear strength is caused by the corroded soil structure resulted from the acid and alkali pollution. The worse of engineering properties is most significant in alkali soils. This research can give guiding significance for the understanding and prevention of water environment deterioration engineering hazards in Yunnan laterite regions.