酸碱污染重塑粉质黏土的塑性及其与力学特性的关系

酸碱溶液会显著改变黏性土的力学特性因而在污染土的研究中备受关注。通过室内试验,详细研究了硫酸、盐酸和氢氧化钠污染重塑粉质黏土的现象、孔隙水离子成分以及土的塑性、压缩性和强度的变化规律。从孔隙溶液的pH值、离子交换以及土的结构三方面解释了硫酸和氢氧化钠污染土塑性增大、盐酸污染土塑性减小的机理。给出了这3种污染土的力学特性与塑性指标之间的关系,并与一些用于非污染重塑土的经验公式进行了对比。发现这3种酸碱污染土均表现出一定的结构性,尽管结构性形成的机理并不相同,但均导致压缩性增大,适用于非污染重塑土的经验公式会低估这类污染土的压缩性。研究发现这种低浓度的污染土的结构性不足以改变不排水抗剪强度cu与液性指数IL之间的关系,因而其强度可以大致通过未污染土的cu–IL关系来预测。

Plasticity and its relationship with mechanical properties of a remolded silty clay contaminated by several acids and bases

The fact that the mechanical properties of clay can be significantly changed by acid and base solutions draws high attention in the study of the mechanical properties of contaminated soils. The change of ionic composition of pore water, soil plasticity, compressibility and strength of the remolded silty clay soaked by sulfuric acid, hydrochloric acid and sodium hydroxide solutions are investigated. The mechanism of the increase of plasticity by sulfuric acid and sodium hydroxide contaminated samples and the decrease of plasticity of hydrochloric acid samples are explained from three aspects: pH value, ion exchange and soil structure. The relationships between mechanical properties and plasticity indexes of the three types of contaminated soils are presented, and they are compared with the empirical formulas for uncontaminated remolded clay. It is found that although the mechanisms are not the same, the three types of contaminated soils show a certain structural effect, which leads to the increase of compressibility. Therefore, the empirical formulas between plasticity and compressibility for uncontaminated remolded clay will underestimate the compressibility of these contaminated samples. However, the structural effect is not sufficient to change the relationship between undrained shear strength c_u and liquidity index I_L, so the strength of contaminated samples can be approximately predicted through the relationship between c_u and I_L of uncontaminated samples.