Experimental study on the permeability of Pb-contaminated silt solidified by CFG.

The permeability of soil is a fundamental parameter in hydrological and geotechnical studies, nevertheless, the investigations on the silt especially the heavy mental contaminated silt have rarely been reported. The research introduces the effect of the different factors, including the osmotic pressure, curing time, the content of binders and the concentration of lead, on the permeability and microscopic properties of lead-contaminated silt, which is solidified by a novel curing agent, formed by mixing cement, fly ash and desulphurization gypsum (CFG). According to the tests of the permeability and scanning electron microscope (SEM), the permeability of samples is investigated under different influencing factors. The results demonstrate that the permeability coefficient of the contaminated silt increases with the increasing osmotic pressure and lead ion concentration, while decreases with the increasing CFG content and the curing time, additonally, there are interactions among various factors, which jointly affect the permeability of samples. Moreover, the statistical analysis shows that osmotic pressure has the most significant effect on permeability among various factors. Besides, the influence of lead ion concentration, osmotic pressure and CFG content on the permeability coefficient at the curing time of 14d is more significant than that of 28d, and the influence order of factors was slightly different at different curing time. Furthermore, the SEM test proves the conclusion of the statistical analysis, which also explains the common reasons for the enhancement of the impermeability and unconfined compressive strength (UCS) of the lead-contaminated silt with the increasing curing time.

Study on mechanical and permeability characteristics of nickel-copper-contaminated soil solidified by CFG.

The study introduces the potential use of a novel curing agent formed by mixing cement, fly ash, and desulfurization gypsum (CFG) for the stabilization/solidification of nickel-copper-contaminated soil. According to the tests of the unconfined compressive strength (UCS), permeability, and scanning electron microscope (SEM), the samples' characteristics, which include UCS, deformation, and permeability, are investigated under different curing time, ion concentration, and curing agent content. The correlation between the UCS and permeability of samples is estimated. The results demonstrates that the gradual increase of the UCS and impermeability of the samples can be recognized with the increase of curing age; however, the failure strain decreased gradually but the trend is reversed with the increase of heavy metal concentration. Besides, greater amounts of CFG results in better mechanical and impermeability properties. The correlation between UCS and permeability coefficient reveals that the UCS of contaminated soil is significantly negatively correlated with permeability coefficient, and the prediction formulas of permeability coefficient based on age and CFG content are given respectively. Moreover, the microscopic analysis demonstrates that the hydration products calcium silicate hydrate(C-S-H) and ettringite (AFt) of CFG curing agent are the main reasons for the enhancement of the UCS and impermeability of contaminated soil. However, the increase of nickel and copper concentration leads to the decrease of hydration products and the compactness of solidified soil, which is the reason for the weakening of the compressive strength and impermeability of contaminated soil.