| Summary: | 碩士 === 國立臺灣大學 === 土木工程學研究所 === 101 === The framework of the critical state soil mechanics has been estabilished through theoretical derivation and many experimental test results. Under this framework, the elastic-plastic Modified Cam Clay model is capable of predicting the deformation behavior of clay after loading. In addition, the development of state parameter under the concept of critical state can also be used to predict in-situ soil properties and deformation behavior. Therefor, critical state soil mechanics can bring many help in engineering analysis design.
However, it is indicated in the literatures that the relationship between the void ratio and the mean effective stress at critical state of sand does not uniquely exist, which differs from the fundamental definition of critical state soil mechanics. Hence, we need to clarify the critical state of sand.
For clarifying the critical state and constitutive behaviors of qartz sand, this research carried out a series of triaxial compression tests. Test variables include relative density, drainage condition, effective confining pressure, and different test methods, namely the triaxial tests with lubricated end platens and unloading-reloading triaxial tests.
The test results show that relative density affected shear strength, volumetric strain, stress-strain curve, and critical sate. It is the most important variable in triaxial test of sand. When the specimen height-to-diaimeter ratio is more than 2.4, the end platens have minimum effects on influencing shear strength and critical state. Further -more, sample preparation method and stress paths have little effect on critical state line. Test results also indicated that the relationship between the void ratio and the mean effective stress at critical state of quartz sand is not unique, where the initial void ratios may have effect on critical state conditions. According to test results, critical state of sand needs to be further studied.
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