# Seismic Performance of Dam Piers Retrofitted with Reinforced Polymer Cement Mortar
## 1 Introduction  
Dams are constructed mainly for flood control and water use. A dam pier is a tower-shaped reinforced concrete (RC) structure that opens and closes gates, such as spillways installed at the top of a gravity dam, as shown in Figure 1. It supports the drain gates attached to the dam, and thus crucial to water storage. If the dam pier breaks down during an earthquake, the water storage function of the dam is lost and there is a significant impact on the surrounding environment; therefore, the seismic resistance of the dam pier must be carefully considered. However, some dams in Japan have severely deteriorated due to aging. To improve their earthquake resistance, various reinforcement methods that are used for bridge piers [1] have been considered for dam pier reinforcement, such as retrofitting with concrete, steel jacketing and fiber sheets [2; 3; 4; 5; 6]. The reinforcing effect of these methods has been confirmed by some studies, but it is difficult to use these methods to strengthen dam piers. Owing to the structural characteristics of dam piers such as the one shown in Figure 1, there are limitations involved in their reinforcement: (i) it is difficult to install a formwork on the dam body; (ii) to reduce the percentage inhibition of the cross-sectional area of a river, the cross-section after reinforcement should not be as large as possible, (iii) if the weight increase due to the reinforcement is large, it will affect the dam body; (iv) as shown in Figure 2, only partial reinforcement is possible owing to the influence of gates and water storage. In light of these restrictions, the applicationof the SRS (seismic retrofitting using cement mortar for shotcrete) method is considered to be optimal for reinforcing dam piers. This method involves the placement of rebar on the existing parts of the dam and then spraying polymer cement mortar (PCM) after scraping their surface. In this study, the reinforced part on which the PCM is sprayed after the reinforcing bar is attached is called reinforced polymer cement mortar (RPCM). As shown in Figure 3, this method is suitable for partial reinforcement. It is possible to reinforce the existing part by installing the reinforcing bar on the existing concrete part after chipping and spraying PCM on it. In addition, this method has the advantages of a lesser reinforcement thickness than the conventional RC winding method, no need to install formwork and suitability to partial reinforcement. This method is easy to apply partially and can reduce the reinforcement thickness and additional mass because reinforcement is performed after scraping the surface. This means that the SRS construction method can reduce the risk that an increase in the structure's weight will increase the seismic load. Furthermore, by using PCM for the surface layer, which has a dense internal structure, high permeability resistance can be ensured, so it can be said that this method is suitable for dam piers. Many past studies on the seismic resistance of dams have examined the seismic resistance of the entire dam structure [7; 8; 9; 10]. However, there are few studies on the seismic resistance of dam piers that are relevant to the present study. In addition, many studies have been conducted on the bending reinforcement effect of reinforcement methods such as RC winding reinforcement, steel plate winding reinforcement and fiber reinforcement as a method of reinforcing similar structural members such as RC piers. However, few studies [11; 12] have been conducted on the reinforcement effect of the SRS method. [PERSON] et al. [11] confirmed the seismic retrofitting effect of this method by reinforcing RC column specimens that modeled existing bridge piers by the SRS method and by conducting a peak-to-peak alternative load test that assumed earthquake conditions.