# Failure Behavior Attributed to Internal Erosion Caused by Conduit Cracks in Homogeneous Embarment
## 4 Conclusions  
This study proposed that the structural faults of deteriorated conduits cause reservoir embankment failure, the mechanism of which was analyzed by examining the failure shape, pore-water pressure, and settlement. The experimental results were compared with the seepage characteristics determined by the three-dimensional seepage-deformation coupled analysis. Based on the results, the following conclusions were drawn:  
1. An increase in the erosion depth is an important indicator that embankment failure, owing to the expansion of the slope failure, is imminent. However, because the erosion depth increases over a very short period of time, measurement methods are limited in their ability to detect rapid changes. This suggests that applying pre-reinforcement to the slope can be an effective method for suppressing the erosion depth, and discussions regarding the reinforcement method at the top of the conduit are necessary. The model experiment results can provide basic data on how to repair and reinforce the conduit of the deteriorated reservoir. They can also be used to identify the piping mechanism in the conduit and predict the possibility of failure;
2. The pore-water pressure and settlement were measured, and the results indicate that they exhibited abrupt decreases and increases at the time of embankment failure, respectively. All the measured values generally corresponded to the time at which failure occurred. The pore-water pressure increased slightly as piping progressed, and then decreased rapidly as the dam crest failed. The differences in pore-water pressures above and below the conduit were determined to be attributed to seepage, and the likelihood of internal erosion was greater in regions above the conduit. The pore-water pressure above the conduit continuously increased, even though the water level within the embankment reached a steady state. This may have created a critical region for internal erosion. In the downstream conduit position, the time over which the pore-water pressure decreased was slightly shorter than in other locations; hence, failure occurred very fast at this location;
3. The hydraulic gradients were distributed below the conduit and gradually extended toward the regions above the conduit of the downstream slope. The results indicate that piping above the conduit near the downstream slope was likely. The stability of the piping owing to the conduit leakage was evaluated by the critical hydraulic gradient. The exit hydraulic gradient in the risk zone of the downstream slope was in the range of 0.5-0.75, and the stability of the embankment was smaller than the reference safety factor (SF = 2.0). By tracking the vulnerable areas of the slope based on the hydraulic gradient distribution and the experimental results, it was determined that a potential failure surface could be formed at heights equal to 1.4-2.4 times (h2) the height (h1) of the downstream side's conduit;
4. Reviewing the settlement in the analysis, it was found that the settlement was concentrated in the central zone of the embankment where the conduit was located. Under these conditions, if the increase in PWP and the action of self-weight continue in the central zone of the embankment, it is presumed that it will be the first risk area that threatens the stability of the embankment;
5. The evaluation of the time of failure based on the experimental and analysis results and the amount of water storage capacity in the Sandae Reservoir indicated that the measurement method (settlement and water storage capacity) was less sensitive to deformation changes than the monitoring method.