Cu(Ⅱ)污染作用下膨胀土的胀缩时程效应研究

TIME EFFECT OF EXPANSION AND SHRINKAGE OF EXPANSIVE CLAY CONTAMINATED BY Cu(Ⅱ)

为探讨Cu(Ⅱ)对膨胀土胀缩特性的影响,针对初始状态相同的膨胀土试样,采用浓度为2.5 g·L^(-1)、5.0 g·L^(-1)、10.0 g·L^(-1)的CuSO_(4)溶液以及去离子水进行处理,开展一系列重金属Cu(Ⅱ)污染作用下的胀缩性试验,并运用Does Response模型对胀缩时程曲线进行描述;利用马尔文激光粒度测试,分析了污染前后膨胀土的粒径分布特征。结果表明:膨胀土试样的膨胀率、收缩速率、竖向收缩率及膨胀含水率皆随Cu(Ⅱ)浓度的增大而增大,但膨胀土试样的损失含水率并不随Cu(Ⅱ)浓度的变化而变化;试样的无荷载膨胀时程曲线可分为快速增长、变减速及缓慢增长阶段;膨胀土的收缩过程可分为缓慢收缩、快速收缩与收缩稳定阶段;Does Response模型不能完全适应无荷载条件下的膨胀时程曲线,但能较好地描述收缩时程曲线;随着Cu(Ⅱ)浓度的增大,未污染膨胀土颗粒在80μm处的粒径分布峰值消失,在47μm处的粒径分布峰值往小粒径方向偏移,说明胶结物逐渐溶蚀,引起部分膨胀土大颗粒分解,依附在土颗粒表面的水膜面积增大,膨胀土吸水能力增强,进而导致高浓度环境中的膨胀土胀缩性较高。

Contamination of heavy metal always leads to the change of engineering characteristics of soil.In order to discuss the influence of Cu(Ⅱ)on the expansion and shrinkage characteristics of expansive clay,we used CuSO_(4) solution with concentration of 2.5 g·L^(-1),5.0 g·L^(-1),10 g·L^(-1) and deionized water to soak samples made of expansive clay.Then,we conducted series of expansion and shrinkage experiments to investigated expansion and shrinkage characteristics.We tried to use Does Response model to fit the deformation process of expansion and shrinkage.Through experiment of Malvern laser particle size,we analyzed the particle size distribution of expansive clay before and after contamination.The results show that rapid growth,variable deceleration and slow growth stages constitute the non-load expansion deformation process,and slow shrinkage,rapid shrinkage and stable stages constitute the shrinkage process.The deformation process of expansion can be described in sections by Does Response model and power function,while the process of shrinkage can be just described by Does Response model.The expansive rate,water absorption quality,shrinking rate and vertical shrinkage rate of expansive clay increase with the increase of Cu(Ⅱ)concentration.However,the loss water content of expansive clay does not change with the increase of concentration.With the increase of Cu(Ⅱ)concentration,peak value of particle size distribution at 80μm disappeared,and the peak value at 47μm change into a value representing smaller particle size.It is proof that the cement dissolves gradually,which causing the decomposition of some large particles of expansive clay.Thus,specific surface area of expansive clay increases and the area of water film attached to the surface of clay particles also increase.As a result,water-absorbent capacity enhances.This brings about higher expansion and shrinkage of expansive clay in high concentration environment.