Research On Change Laws Of Water Content In Sandy Soil Embankment With Laboratory Test

Sandy soil is a kind of subgrade filler with good gradation, high strength and excellent performance, but its performances are obviously influenced by the changing water content. For this reason, through choosing the subgrade filler of sandy soil from the extension project of Fo-Kai Expressway in Guangdong Province, the thesis researched the change laws of inner water content of soil sandy embankment with the similar model test in the laboratory and the test method of electric resistance.1) The test results of granular analysis, limit water content, heavy compaction, scanning electron microscopy and other methods showed that the uniformity coefficient and the curvature coefficient of the experimental soil are 7.54 and 2.89, the liquid limit and the plastic limit are 22.2% and 15.8%, and the maximum dry density and the optimum water content are 9.5% and 1.88g/cm3, respectively. These indicate that the soil is well in gradation, easy to compact, main in single granular structure, and more uniform in granular distribution, as well as the small particles are attached to the large particles. Then the experimental soil is named as clayey sand SC in engineering.2) Through the tests of the modified permeability of normal water-head and the capillary water rising, the soil permeability coefficients are negatively correlated with the compactness and the fine granular content, and all the correlation coefficients are more than 0.9. Both influence the soil permeability by affecting the void ratio. The water content is higher, the rising speed of capillary water is slower, because the higher water content and the smaller soil suction. The compactness is greater, the rising height of capillary water is greater, but the initial rising speed is slower. The influence of temperature on capillary water is relatively weak, the higher the temperature and the faster the capillary water rising.3) The conductive characteristics of clayey sand SC are studied by the self-designed tests, and the results show that the soil electric resistances are most sensitive to water content changes in both ends of the probe diameter of 5cm around. The soil electric resistances are negatively correlated with the compactness and the water content, and there are very good correlations of line and power function, respectively, and the correlation coefficients both are more than 0.9. So the test mehod of the soil electric resistances can be applied to reflect the changes of water content. 4) The indoor similar model of embankment was made for the tracing observation, and the results show that there is a well positive correlation between the inner water content and the depth in the model, as well as the greater the depth and the greater the water content. However, the change curve of water content with depth from the field observation shows a"C-type"curve generally, as well as the middle is low, but both the upper and the lower are high, because the indoor model does not come into contact with more rainfalls. During the last December to the next May, the change laws of water content in the model are basically consistent with the field observation. For the change correlations between water content and temperature, the results of indoor embankment model are also basically consistent with the field observation, and the changes of water content to the changes of temperature exist a different degree of delay, as well as the greater the depth and the more obvious the delay.In summary, the changes of inner water content in sandy soil embankment are the comprehensive effect results of compactness, temperature, ground water and other factors. The change laws of inner water content in the model with the test method of electric resistance are basically consistent with the field results with the tracing observation.