Experimental Study On Complex Stress Path Of Coarse Grained Soil

The coarse grained soil has been applied widely in a lot of projects, such as earth-rock dam, railway, roadbed of highway, bridge pier and soft foundation. Especially in earth-rock dam, it has been used as main embankment material, so its mechanical properties are greatly important to safety and operation of projects. But the research into coarse grained soil is not enough at the present time, its basic qualities need to further studies. In addition, Duncan-Chang model is used generally in earth-rock dam's FEM, but it is built on mechanical properties of clay. Therefore it still needs to be proved that weather Duncan-Chang model can be used in coarse grained soil and especially weather it can reflect mechanical properties of coarse grained soil in different stress paths. According to these questions, some work has been done in this dissertation.Firstly, former triaxial apparatus are improved to adapt to designed-test requirements. Some programs are compiled to control various stress paths. Test apparatus include electronic universal testing machine, GDS water pressure controller and a automatic controlling and recording data system developed on the basis of visual basic language.Secondly, a series of CD tests for dam shell coarse aggregate with different densities of specimen are performed, the shear properties of coarse grained soil and the influences of densities on strength and deformation are analyzed on test results basis. Conventional triaxial tests of coarse grained soil with geotechnic cloth and without geotechnic cloth are proceeded and the mechanism of action of geotechnic cloth is studied. Rubber membrane penetration on volume change is measured by CIU tests, the hyperbolic relation between rubber membrane penetration on volume change and confining pressure is obtained.Thirdly, constant p and constant q stress path tests for coarse grained soil with different densities are carried out, the effects of densities on stress-strain relationship and deformation qualities under special stress paths are analyzed, shear yield surface and volume yield surface are fitted on the basis of test results. In addition, constant stress ratio tests for coarse grained soil are performed and deformation qualities under this stress path are researched.Finally, according to the test results of coarse grained soil, it is found that the relationship between axial stress and axial strain of coarse grained soil coincide with hyperbolic curve, which is a postulate in the Duncan-Chang model. But the postulate which is the relationship between lateral strain and axial strain coincide with hyperbolic curve in the Duncan-Chang model is not suitable for coarse grained soil. And it is also found that the Duncan-Chang model can not reflect the stress-strain relationship of coarse grained soil under the stress path of constant stress ratio.