Laterite Dam Diseases Chloride Ion Erosion Mechanism

China is abundant with water resources, which is very uneven in regional distribution and seasonal rainfall also hard to meet the demand. Therefore, a lot of dams, a large part of which are earth-rockfill dams, are built to meet the requirement of irrigation waters and electricity and prevent floods and drought. However, owing to historical reasons, serious problems exist in these dams and the variation of physical and mechanical characteristics is the major factor that causes the dam breaks, which occupies a large proportion in the reasons that cause home and international dam breaks. Current analysis of the root cause of the diseases is restricted in the aspect of physical and mechanical characteristics without giving full consideration to the variation of physical and mechanical characteristics caused by chemical reaction in the reservoir water environment. Supported by the national natural science fund and taking Tian Long Qin reservoir as its archetype, a comprehensive analysis of the sources of pollution is presented considering a large existence of Cl1- in the reservoir water,meanwhile, the water and soil mechanism of "Cl1-eroding laterite" is fully got based on the study of physical and mechanical character,microscopic structure characteristics and quantized characteristic parameter of laterite eroded by Cl1-.The achievements can be used as a reference in the consolidation to solve dam problems by the root.Basic physical characteristics permeability coefficient,compression coefficient,sheer strength,critical moisture content and change of components of material of earth-rockfill dams before and after eroded by Cl1- is studied based on chemical accelerated experiments and conventional physical mechanics texts, Chemical composition analysis test, microstructure observation test. Meanwhile, comparative analysis is made for the data of the soil samples before and after eroded by Cl1-. The results turn out that physical and mechanical characteristics are changed obviously in the erosion soil samples compared with original soil samples. The mainly displays are:Decreasing in density, moisture content and specific gravity; Increasing in compression coefficient, decreasing in compressive modulus; Different degree of decreasing in shear strength under different vertical pressure; Increasing in permeability coefficient; Decreasing in liquid-limit and plasticity index, increasing in plastic limit; Increasing in the content of sands and silt and decreasing in the content of clay and micelles. All the data shows clearly that the Cl1- in the reservoir water will affect the physical and mechanical characteristics of laterite that used as material for earth-rockfill dams.Through observation of microstructure characteristics of the soil samples of different concentration of HCl solution by Electronic scanning microscope and analysis of microstructure images of different magnification factor, the result is got that there is a dense apparent structure good solidity in the uneroded laterite by Cl1- and space between the granules is filled with cement. However, as for erosion laterite, there are a number of indications that the cement between the granules is dissolved. Pore of the soil get increased as the content of cement decreases obviously, which makes the soil not dense any more.Based on the analysis of the main reasons that bring the physical and mechanical characteristics of materials of dams down, a conclusion is drowned that:the Cl1- in the reservoir water react with the various free oxide, soluble salts, insoluble salts and other cements which play a role of cementation and framework in laterite soil and produce soluble salts and they could be easily taken away by osmotic water and by mean of which it bring the physical and mechanical characteristics and microstructure characteristics of the soil down. The effect is even more visible for laterite soil which has a good engineering property and is rich in cements and carbonates. The study and its conclusion is of obvious theoretical reference meaning and mass practical value in the design of consolidation of earth-rockfill dams located at acid laterite areas.