# A Comprehensive Safety Analysis Study for Concrete Core Dams
## 1 Introduction
### Proposed Calculation Model
#### 1.1.2 Proposed Method  
Based on the demand for seepage calculation and analysis of earth rock dam engineering with a unique core wall form, the seepage is calculated according to the principle of the virtual point method and is realized based on element birth and death technology. Firstly, the position of the phreatic line is assumed, and the iterative calculation is continued until the difference between the two iterations meets the limit. The phreatic line is analyzed, and the position of the escape point is found. Then, the total seepage flow is calculated. Under similar boundary conditions, the seepage field can be analyzed through the thermal analysis module; however, it is more appropriate to use the birth and death element technology for the phreatic line problem, which requires secondary development. The seepage of an earth rock dam with a unique core form has a free surface, which is called saturated soil below the free surface and has a fixed permeability coefficient. The part above the free surface is considered not to participate in the seepage calculation. For the definite solution conditions, it is assumed that the normal seepage velocity of the phreatic line is zero. The idea of secondary development is: the position of the phreatic line is assumed, the downstream outlet of the earth rock dam project with a unique core wall form is continuously calculated according to the assumed boundary conditions, and then the tolerance is set. When the difference between the total head calculated twice meets the given tolerance, the calculation result will be obtained. The calculation of free surface is one of the difficult problems in seepage analysis. The free surface of seepage is the boundary to be determined in the seepage field, which needs to meet both the first and second boundary conditions. In most current fixed grid methods, the calculation of determining the free surface is more complex and highly dependent. This paper proposes to use the local grid change method to analyze the hazard removal and reinforcement project of this unique core wall-type earth-rock dam project. The above method can not only simply change the grid of the old iteration to the grid required after the new iteration, but also use the body-fitted coordinate transformation technology to make the grid of each iteration process completely regenerate (Figure 1). According to the above process, it is necessary to assume the outlet point position of the phreatic line, and use single-element birth and death technology to continuously \"kill\" the elements above the phreatic line; only the parts below the phreatic line participate in the calculation. It is always in the \"live\" state and continues to circulate until the tolerance is met. According to the above ideas, the command flow for seepage analysis and calculation is prepared and verified by a practical example: assume that the dam height of the homogeneous earth dam under study is 20 m, the dam crest is 6 m wide, the bottom is 80 m wide, the upstream slope ratio is 1:1.5, and the downstream slope ratio is 1:2.2. The working condition is that the upstream water depth is 18 m, and the downstream water is free. See Table 1 for the relationship between the void pressure value and the permeability coefficient index. Homogeneous dam refers to a dam that is composed of most of the dam body filled with homogeneous soil materials. The whole dam body of the homogeneous dam (except for the drainage facilities) is made of soil with low permeability. The pore water pressure dissipates slowly during the construction period, which is unfavorable to the settlement and stability of the dam body during the dam construction. Therefore, it is not suitable to use fat clay with a high clay content. Figure 1: Proposed calculation model for seepage. The reason for choosing the above homogeneous earth dam is that a consistent conclusion has been reached for the water conservancy project. Therefore, the basic realization could be used for justification of calculation results.