Experimental Study On Strength Characteristics Of Remolded Loess Under Seepage

Seepage is an important reason for the engineering properties deterioration of loess. The loessial physical and mechanical properties change with complex soil-water interactions carrying on under sustained seepage, which decreases its strength, when it is used as impermeable material. Therefore, it has important engineering significance to study on the law of loessial physical and mechanical properties (strength, chemical constituents, and so on) changing slowly with time-lapse. In view of the difficulty of laboratory simulation, the current researchs are concentrated on the mechanism of soil-water interactions, and little on the loessial long-term strength under seepage. This paper studies on its short-term strength under seepage of different pH solutions and the relationship between its CaCO₃ content and strength under sustained seepage of acidic solution by laboratory simulation, using Q3 remolded loess in Yangling as research object. It relies on the National Natural Science Foundation project"The Research of Properties Deterioration Mechanism of Loess Engineering and Life Prediction of Loess Structures".It includes three chemical interactions with mechanical effect in soil-water interactions: dissolution, precipitation or crystallization, cation exchange adsorption. The water environment between soil particles affect on their occurrence and development. So the short-time strength of loess is different under seepage of different pH solutions. It is found through test that: The strength of loess after seepage of acidic solution is bigger than after seepage of pure water, even more than its initial strength. A series of chemical reaction take place between the bicarbonate in soil and acid under seepage of acidic solution, which produced carbon dioxide gas to increase the strength of loess; The dissolution and precipitation or crystallization of calcareous cement and other soil salinity changed the connection between soil particles, and the cation exchange adsorption changed electric double layer on particle surface. This improved the cohesion while decreased the internal friction angle. It shows a weak correlation between its CaCO₃ content and strength in 10h. This suggests that the dissolution of CaCO₃ is not the dominant factor of loess strength in the early seepage, but it could determine loess strength after long-time seepage. Soil-water interactions are continuous under long-time seepage of acidic solution. The results show that: The time-history curves present wave shape. Based on mechanism analysis, it can be deduced that the peak strength and fluctuation range of the time-history curves will decreased gradually. Comparison study shows that the remolded loess with lower compactness responded badly to external additional load (confining pressures lower than 400kPa), while the time-history curves present strong consistency; But the remolded loess with higher compactness make good respond to external additional load, while the time-history curves are different under different confining pressures, especially lower confining pressures (200kPa).This paper simulated the correlation between CaCO₃ content and the relative change rate of loess strength and builds a simple mathematical model, based on the test results. It is an innovative point of this research. But it needs more work to verify its accuracy, to determine the physical significance and acquisition method of the model.