Alkaline Substances Test On The Red Clay Dam Failure Mechanism

Yunnan Province is located in Chinese southwestern border, which is a typical highland mountainous province and is one of the provinces that laterite is widely distributed. Laterite is acidic and because mountain reservoir sedimentation remains of a large number of animals and plants, organic acids, hydrogen sulfide and other substances have been produced during fermentation and commonly used pesticides, fertilizers are acidic too. These factors all contributed to the water quality of mountain reservoir showing weakly acidic and the acidity of the reservoir water gradually increases with depth.Mistakes have been made in the reinforcement of dams and reservoirs located in mountainous area covered of laterite for a long time. Materials such as the cement, cement clay paste, lime and other strong alkaline substances, are widely used in reinforcement. These materials in hydration will produce large amount of Ca(OH)2,which will produce chemical reaction with the acidic laterite and a large number of the active ingredients that laterite project mechanics need are consumed, and thus physical and mechanical properties of laterite are deteriorated. More regular research shows that the reinforcement of mountainous reservoir projects end with large amount of money putting in and shot benefits getting, which has a strong relation with the wrong use of reinforcement materials. Therefore the research into the interaction between alkaline substances and laterite and finding out the deterioration mechanism of alkaline substances to laterite is highly valuable in the design, selecting of reinforcement materials, saving of investment and prolongation of life of engineering in laterite areas.In this paper, theoretical analysis and laboratory experimenting and prototype validation route are adopted as the main method in the systematic study of the deterioration that alkaline substances in the reinforcement material do to the hydraulic characteristics of the laterite. Due to the limiting of time, the paper is mainly involved the most common substances in the alkaline reinforcement material—calcium hydroxide and accelerated life comparison test is designed based on the relevant theory and the successful examples. Then tests of the soil samples that have been soaked with different concentrations of Ca(OH)2such as moisture content, density, specific gravity, falling head infiltration, compression, direct shear, test of the limits of moisture content and particle analysis are carried out and impact on physical and mechanical indicators of the samples by different concentrations of alkaline solution (distilled water included) is discussed and relevant ion change in the whole infiltration liquid of all soil samples is measured quantitatively and the outcome is compared with real the disease projects. It is showed that deterioration trend of physical and mechanical indicators of the soil samples is obvious after the erosion of the calcium hydroxide and moisture content, permeability coefficient, compressibility, liquid limit, sand and silt content of the testing samples increases with varying degrees, while the density, specific gravity, cohesion, angle of internal friction, plasticity index, clay and colloid content of the testing samples decreases with varying degrees.Conclusions are gotten as follows:(1) the pH value of water medium of the laterite is increased by the alkaline substances in the reinforcement material. As a result, both of the free Fe oxides and Al oxides are negatively charged and produce repulsive force with clay minerals, thus cohesion of laterite is deteriorated.(2) Effective cement substance such as silica sol, alumina is consumed because of the chemical reaction between the alkaline substances and the laterite. Since clay has large surface area and the content of AI2O3is relatively high, the clay is much easier to produce the chemical reaction and then become deconstructed, making the cohesion of laterite decreased and sandy silt slowly showing. The combined effect of pressure and seepage makes the parcel layer of the soil particles and the slow cement slowly deconstructed and particles gradually oozed, resulting much serious leakage on dam.(3) The alkaline substances in the reinforcement material r will also be eroded by the acid soil and water with pressure. Compound produced by chemical reaction which is either dissolve in water or is precipitation of powder is much easily to flow away with pressure water seepage.acid-base reaction between laterite and alkaline substances is right primitive mechanism that agriculture for centuries years adopt to improve acid soil compaction and the primitive mechanism of the relaxation farmland. Chemical reaction gradually bring powder desertification, affinity degradation of the two kinds of materials combined, slowly increasing the gap and the formation of micro seepage channel and ultimately lead to the seepage failure.