Unsteady Seepage Analysis On The Core Wall Dam Considering The Influence Of Unsaturated Soil

Earth and rock-fill dam has the advantage of better adaptability to different geology and climate, using local materials, better economic benefit and higher effective and available method on design, it is always taken into account first in dam lectotype. The seepage is the key effect factor to dam security, enough attention should be taken in the dam design and management, so how to analyses the seepage expediently and accurately is very important. In practical engineering, there is always emergency in the period of reservoir operation, It need to empty water in the reservoir. In the course of dropping water in the reservoir dam project, the unsteady flow in the dam body often causes landslide, so in order to analyses the stability of upstream dam slope, unsteady seepage must be calculated. Unsaturated soil is the soil underground, it has negative pore-water pressure, but at present the seepage in unsaturated soil is always ignored. In fact much engineering is affected by the seepage in unsaturated soil, so considering seepage in saturated soil and unsaturated soil at the same time is very necessary.In this paper, based on the basic equation, the steady and unsteady seepage differential equation is derived with the foundation unknown of the pressure head,2D saturated-unsaturated seepage control equation is also derived by combining the correlation theory of unsaturated soil, and the corresponding definitation is given.At last the finite element discretization is done on the equation by the method of Galerkin, and the finite element format of the 2D saturated-unsaturated seepage control equation is derived, it provides the reliable theory basis for the finite element analysis of the 2D saturated-unsaturated seepage.The saturated-unsaturated steady and unsteady seepage analysis is done for the core wall dam of Wohushan reservoir at different falling speed of the upstream water level. Based on the analysis, the change law of the phreatic line in the dam at different falling speed of the upstream water level is obtained, and analysis on the cause of the flow backwards phenomenon is given. Also, the experimental formula is deducted about the highest point of the phreatic line in the dam. This method provides achievable theory foundation to the dam design and management.