Analysis Of Concrete Dams Based On The Concept Of Generalized Effective Stress

During the strength and stability analysis of dam-foundation system, it is quite necessary to incorporate the action force by water on both the dam part and the foundation. Apparently, a seepage analysis of the whole system is required to obtain a more clear understanding of the water loads. A numerical approach by the finite element method is established in this thesis for calculation of internal deformation and stress field within the dam part, on the basis of a seepage analysis and the generalized effective stress law which is found to be more appropriate for rock and concrete materials. Moreover, a 3-D seepage and stress analysis of Ertan arch dam has been completed with some engineering data and field records as a basis. Main work and contributions of this thesis are presented as below:(1) Based on the fundamentals of seepage theory, some seepage analyses of the dam part have been conducted using the finite element method. Some typical problems during numerical modeling of seepage process are analyzed, such as methods for determination of the phreatic surface and techniques in simulating the seepage control measures. Some preliminary investigation into the effect of control measures on the water redistribution within the dam part is also presented.(2) The mechanical effects of water in saturated pore medium is represented from macroscopic view and concepts of uplift pressure and seepage force are discussed. And, the historical review of the development of uplift is revealed especially. Based on generalized effective stress law, the expression of uplift pressure and seepage force has been deduced and expression of water pressure on gravity dam base in FEM format also obtained; the real physical meaning and influencing factors of uplift pressure of gravity dam is represented; Simultaneously, the correct water-load combination forms is given, and a numerical method more suitable for rock and concrete materials is established.(3) It has been found that the magnitude and application method of water load are related to B value of the pore medium itself, and the choice of B value presents a notable effect on dam displacement and stress. Taking a gravity dam as an example, it is observed that most favorable stress distribution within the dam part is given when B=0, while contrarily a most dangerous stress field is mobilized when B=1. However,it still requires further study to make sure whether the phenomenon is universal.(4) A refined FEM modal is established based on analysis of the geological data and the complicated seepage prevention and drainage measures of ertan arch dam. Seepage and stress of the dam area have been performed sequentially, and the simulated pore pressure and displacement agree well with the monitoring data. It is indicated by the simulation results that the drainage system is comparatively more effective to reduce the pore water pressure than the cutoff wall measure. It is shown by the simulation results that larger tensile stress would be triggered while the compression stress is lowered within the dam part when the B value is increased, which indicates more dangerous stress distribution for the dam part when considering the seepage flow. Therefore, it is of great importance to appropriately consider the seepage behavior during the design of water dams.