Study On Wetting Deformation Behaviour And Numerical Model Of Coarse-grained Materials

The wetting deformation of coarse-grained material is a key problem in design of high earth rockfill dam, but it is not solved well so far. In this thesis the wetting deformation is studied systematically and intensively by wetting deformation test, analysis of test results and numerical simulation.A new apparatus for holding constant stress state is improved for triaxial wetting test. It includes electronic universal testing machine and GDS water pressure controller. It is controlled by a computer, and automatic recording data and different stress path test may be achieved.Using the new apparatus, a large number of tests on coarse-grained material are carried out, and the behaviour of wetting deformation is studied. The relationship between wetting axial strain and wetting volume strain is investigated. The deformation behaviour of wetted soil while loading may be explained on the basis of the elastic-plastic theory. The effect of wetting to the soil shear strength is investigated, and it is found that the shear strength of soil after wetting would not vary with different wetting stress level and they are equal to the shear strength of soil in saturated state. The advantages and limitations of single & double line methods are discussed, and an improved double-line method is suggested. The concept of the maximum wetting stress level is advanced, and using this concept the phenomenon that wetting axial strain under low cell pressure is larger than that under high pressure at high wetting stress level is explained reasonably. In the thesis, the empirical formulas for single-line method for dense coarse-grained material are presented, and its adaptability is discussed.The effect factors for wetting deformation in wetting test, such as time, pause-shear deformation and the deformation steady criterion, are investigated. The relationships of pause-shear deformation vs. time and wetting deformation vs. time are achieved. They demonstrate that the relationships are linear between the deformations above and the logarithm of time after a certain moment. The test results indicate that the pause-shear deformation should be not ignored. The wetting should starts until the pause-shear deformation ceases, otherwise the error for wetting deformation is high. It advances that the moment, at which the steady deformation phase reaches, may be regarded as the criterion for deformation. The rationality of this criterion is discussed later, and at the same time a reference criterion for pause-shear deformation and wetting deformation is suggested.The grain breakage due to wetting is studied by the wetting test. According to the grain breakage test of sample under dry and saturated state, the behavior of particle breakage is revealed. A normalized formula for grain breakage is proposed. Based on the energy analysis, it is found that the power-law function relations exist between grain breakage and external force plastic work against grain breakage energy, and the ratio of grain breakage energy to external force plastic work does not vary with the stress state. It is found that the wetting grain breakage has close correlation to the wetting deformation. It is pointed out that the plastic work of external force provides the energy for wetting grain breakage from the theory of energy. The behavior of wetting deformation is analysed from the point of view of the wetting grain breakage.Based on test results and couple yield surfaces constitutive model, a wetting plastic model is presented. It bases on the classical plastic theory, and the components of wetting deformation under complicated stress state may be determined clearly. It is validated that this model can reflect the wetting deformation behavior of dense coarse-grained material well.Based on analyses to FEM method of wetting deformation in earth rockfill dam, the problems are pointed out, and an improved method to simulate wetting deformation is proposed. With the numerical simulation for Nuo-Zhadu Earth Rochfill Dam, the wetting deformation is investigated. The results show that the problems pointed out in the thesis are exist, and the improved method is reasonable. The wetting deformation tendency from the wetting plastic model presented in the thesis agree well with that observed of the constructed earth dam during the water impounding. This verifies further that the presented wetting plastic model is reasonable. At the last part, the effects of wetting deformation to earth rockfill dam deformation and arch action in core are evaluated.