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

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 CuSO₄ 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 80 μm disappeared,and the peak value at 47 μm 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.