# Failure Behavior Attributed to Internal Erosion Caused by Conduit Cracks in Homogeneous Embarment
## 2 Materials and Methods  
### Model Reservoir  
In embankments exceeding 50 years of age in Korea, filters are often nonfunctional owing to their age [16]. Aging filters may either completely lack filters to protect the embankment or may have inadequate filters according to modern design standards [2]. Additionally, a previous study found that 25% of internal erosion failures were due to the fact of inadequate filtration within the embankment [17; 18]. These studies reveal problems with filter design in older reservoirs and explain the difficulty in ensuring the long-term normal performance of filters from erosion or filter clogging, as the risk of potential failure of the embankment is high in these environments.  
However, if a crack occurs in the conduit, the risk of failure may be considerably high. Nearly one-third of internal erosion failures are closely related to backward erosion piping; the finding that half of them develop erosion along the conduit or foundation contact or as internal erosion along the foundation contact is a reminder of the importance of conduit structures [16].  
Therefore, in this study, an experimental model comprising a homogeneous embankment was configured to investigate the occurrence of failures on the embankment slope owing to conduit leakage. The experimental model was designed as a prototype at a scale of 1:20. The height, width, and length of the model were 76, 126, and 540 cm, respectively. The model slope inclinations (vertical distance: horizontal distance) were 1.0:2.0 and 1.0:2.5 in the downstream and upstream slopes, respectively.  
The guidelines stipulate a high homogeneity of geotechnical properties for construction materials to control infiltration in the design of an earthen dam. In the design and analysis of earthen dams, the permeability coefficient is assumed constant regardless of the depth and location of the embankment; however, in practice, it is nonhomogeneous and anisotropic [17; 18]. This inhomogeneity and anisotropy, along with many variables, complicate the seepage flow within the embankment. Therefore, in this study, the following two methods were considered for model construction:  
1. For the model embankment, only soils that passed through a 12 mm sieve were used to ensure that the specimens could be laid homogenously. Additionally, the compaction moisture content was adjusted to the optimal moisture content (14 \(\pm\) 2%);
2. To achieve a uniform density, each layer had an approximate thickness of 10 cm, and the compaction was made with a vibrating machine (frequency: 9000-12,000, 50 Hz) until approximately 90% of the maximum dry density was reached.  
As described above, the permeability coefficient of the embankment zone is considered isotropic due to the controlled soil particle size and compaction process. However, at the boundary between the conduit and embankment zone, soil erosion or loss occurs, possibly increasing the change in velocity head. Accordingly, while anisotropy is unavoidable around the conduit, erosion due to the homogenization of the embankment zone can yield consistent results.  
Table 1 lists the physical and mechanical properties of the soils used in the experiments. All values listed in Table 1 were obtained by laboratory tests, with each value calculated according to American Society for Testing and Materials (ASTM) standards.