Experimental Research On Soil Contaminated By Acid And Alkali

With the development of urban construction, the environmental pollution is rapidly increasing, and the contaminated soils have increasing influence on the engineering construction. The research on contaminated soil becomes one of the popular problems and obtains much attention in the domain of environmental geotechnology. Based on laboratory tests, the mechanism of chemical corrosion, the physical-mechanical property and the microstructure of soil contaminated by acid and alkali are studied, as follows:(1) Based on the method of soak in laboratory, the hydrochloric acid and sodium hydroxide in different consistence are used to prepare the contaminated soil. The colors of acid and alkali are changed after the soil pollution, and it is caused by the ion-exchange between the mineral element of soil and the chemical solution.(2) Based on the determination of mineral element before and after the soil pollution, the main constituents of clay mineral are kaolinite and illite, which are not reacted with acid or alkali generally. The contents of oxide dissociative and water miscible salt have changed in the chemical reaction, such as corrosion and deposition, and new mineral elements are created. Because the humic acid and fulvic acid in the humic matter react with acid and alkali, with the increasing of consistence of acid and alkali, the organic content of soil deceases. Based on the ion-exchange, the membrane of bound moisture becomes thicker with the ions of the solution entering it, which causes the change of physical-mechanical property.(3) According to the determination of the physical-mechanical property before and after the soil pollution, with the change of consistence of acid and alkali, the physical-mechanical properties of soil, including mass, density, water content, specific weight, porosity ratio, liquid limit, plastic limit and plasticity index are affected. Besides, the deformation behavior and the shear strength of the soil sample are also change after the corrosion. The reasons of these changes are that the soil has chemical reaction with acid or alkali, which results in the change of mineral element and the destroying of soil structure, and some specials ions enter the membrane of bound moisture and affect its thickness, which lead to the change of innergrannular force between the soil grains.(4) The microstructure of the soil contaminated by acid is investigated with scanning electron microscope, and the parameters of microstructure are analyzed with the image processing program Geolmage. With the increasing of consistence of acid, the proportion, the distributing fractal dimension and the degree polymerization of grain decrease and those of pore increase, the Euler's number of the soil increase. Some parameters which belong to the macroscopical physical-mechanical property have correspondence with the parameters of microstructure, and the changes of the microstructure and the macroscopical property have the strong interaction.