# Centrifugal Model Study of Seepage and Seismic Behavior in a Homogeneous Reservoir Dam with Parapet
## 1 Introduction  
Localized torrential rains owing to climate change have caused extreme flooding and resulted in overtopping-induced embankment failure worldwide for the past several years [1,2]. The increasing frequency, duration, and intensity of natural disasters has heightened the importance of future disaster risk management in the community [3, 4, 5]. In 2020, 41 deaths and damage to 1057 hydraulic facilities were reported in Korea due to torrential rainfall between 24 June and 16 August, the longest such period in history. Additionally, 22 small-scale reservoir dams collapsed during this period [6,7]. Most of the reservoirs that failed were fill-type embankments (H \(\leq\) 15 m) built over 50 years ago, with their failure caused by overtopping. Figure 1 shows the relationship between the August rainfall and reservoir failure in Korea between 2010 and 2020. Rainfall in 2020 (657 mm), which caused the failure of small reservoir dams, was the highest during the 2010-2020 period. Although rainfall in 2002 (688 mm) and 2003 (684.2 mm) was higher than that in 2020, only one to two reservoir failures were reported. However, by 2020, 85.6% of reservoirs aged above 50 years had collapsed, with earth-fill dams accounting for 99.8% of all reservoirs [8], implying that overtopping was not the only trigger for damfailure. Table 1 shows the causes of reservoir dam failures for the 2010-2020 period, with most failures attributed to torrential rainfall. Some failures were also caused by piping defects due to aging conduits. Although determining the exact cause of dam failure is difficult, it is evident that the failures occurred in dams over 50 years old, potentially because of construction and maintenance issues linked to the prevalence of homogeneous reservoir dams built under poor social conditions during the Japanese colonial period and the Korean War (1930-1970) [9]. Most small reservoirs constructed during this time lacked proper flood protection and control measures or maintenance, increasing the risk of dam failure today. In addition, overflow accounted for the highest failure rate (35.9%) in fill-dam-failure statistics [10], with such failures often attributed to unfavorable physical soil conditions, including compacted soil, soil moisture, and clay content. These conditions can lead to flooding as water levels rise uncontrollably due to soil erosion or structural defects [11; 12]. These findings suggest that preventing flooding in old reservoirs, which continue to increase every year, is difficult when torrential rains exceed the designed flood level. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Years**} & \multirow{2}{*}{
\begin{tabular}{c} **Number of** \\ **Failures** \\ \end{tabular} } & \multicolumn{4}{c}{**Cause of Embankment Failure**} \\ \cline{3-5}  & & **Dam Type** & **Cause** & **Note** \\ \hline
2010.8 & 2 & Homogeneous-type & Torrential rain & - \\ \hline
2011.8 & 1 & Homogeneous-type & Torrential rain & - \\ \hline
2012.8 & 1 & Homogeneous-type & Torrential rain & - \\ \hline
2012.8 & 2 & Core-type & Torrential rain & - \\ \hline
2013.4 & 1 & Homogeneous-type & Deterioration & Conduit defect \\ \hline
2013.7 & 2 & Core-type & Torrential rain & - \\ \hline
2014.8 & 1 & Homogeneous-type & Torrential rain & - \\ \hline
2014.9 & 1 & Homogeneous-type & Torrential rain & - \\ \hline
2014.9 & 1 & Core-type & Deterioration & Conduit defect \\ \hline
2016.10 & 2 & Zoned fill-type & Torrential rain & - \\ \hline
2018.7 & 1 & Homogeneous-type & Torrential rain & - \\ \hline
2019.10 & 3 & Zoned fill-type & Torrential rain & - \\ \hline
2020.7 & 1 & Homogeneous-type & Deterioration & Conduit defect \\ \hline
2020.8 & 3 & Homogeneous-type & Torrential rain & - \\ \hline
2020.8 & 13 & Core-type & Torrential rain & - \\ \hline
2020.8 & 5 & Zoned fill-type & Torrential rain & - \\ \hline Total & 40 & & - \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Causes of failure of reservoir dams during 2010-2020. Figure 1: Relationship between rainfall and reservoir failure (Korea).