# Stability Improvement Method for Embankment Dam with Respect to Conduit Cracks
## 2 Materials and Methods
### Experimental Models  
The experimental models for the conduit were the current model, which was used at the site, and the improvement model proposed in this paper. Figure 2 shows an overview of the current and improvement models.  
The current model covered the outside of the conduit with a layer of clay to relieve water pressure on the conduit. Most old reservoirs (over 50 years) in Korea are designed similarly to the current model. However, as the facilities have recently deteriorated, the structural environment of these conduits has become increasingly uncertain regarding the stability of the embankment. For example, the loss of clay particles over time is unavoidable, which naturally increases the pressure that the conduit receives from water. Furthermore, increased water pressure in aging small reservoirs can potentially cause problems such as erosion and piping phenomena on the downstream slopes. In a fill-type embankment, the failure rate of the piping is high (30.5%) [18]; thus, it was necessary to additionally devise a method to reduce the water pressure on the downstream slope.  
\begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{\(\mathbf{G_{s}}\)} & \(\mathbf{PI}\) & \(\mathbf{W_{opt}}\) & \(\mathbf{\gamma_{max}}\) & \(\mathbf{c}\) & \(\mathbf{Q^{\circ}}\) & \(\mathbf{k_{\mathrm{p}}}\) & \multirow{2}{*}{**USCS**} \\  & & **(\%)** & **(\%)** & **(kN/m\({}^{3}\))** & **(kPa)** & & & **(m/s)** & \\ \hline Clay layer & 2.76 & 8.6 & - & 13.66 & 29.43 & 0 & 3.70 \(\times\) 10\({}^{-9}\) & CL \\ Embankment & 2.65 & 9.2 & 8.6 & 17.75 & 16.70 & 24 & 2.37 \(\times\) 10\({}^{-7}\) & SC \\ Sand layer & 2.65 & NP & 12.7 & 17.00 & 0 & 33 & 7.82 \(\times\) 10\({}^{-4}\) & SP \\ Geotextile & - & - & - & - & - & - & 1.00 \(\times\) 10\({}^{-3}\) & - \\ \hline \hline \end{tabular}
\end{table}
Table 1: Physical and mechanical properties of samples used in the model.  
Figure 1: Experimental model and measurement location.  
In this context, the improved model presented in this study is a method of applying a layer of sand and geotextiles on top of the clay layer in the current model. The purpose of this additional layer is to install a sand layer on the downstream slope to prevent the leaking water from rising to the downstream embankment zone and to apply geotextile to prevent the loss of soil particles.  
In a general embankment dam, a drainage structure such as a toe drain or filter is located at the end of the downstream slope of the embankment to stably drain the seepage water. However, when erosion starts at a crack in the conduit, the drainage structure installed at the end of the downstream slope induces rapid drainage of the seepage water, which may increase the risk of internal erosion.  
Here, the general premise of the improvement model is that when a sand layer and geotextile are placed on the upper part of the conduit, the water pressure concentrated on the crack surface of the conduit is dispersed into the sand layer to induce a delay of internal erosion. The improved model differs from the general embankment dam drainage structure in that it is designed in consideration of the prevention of potential piping due to conduit cracks. Table 2 lists the experimental cases for the current model and the improvement model.  
In the current model, the erosion characteristics and the effectiveness of reinforcement were evaluated under cracking conditions in the conduit (Section A).