Experimental Study on the Axial Compression Performance of an Underwater Concrete Pier Strengthened by Self-Stressed Anti-Washout Concrete and Segments  
[PERSON]  
1 College of Civil Engineering, Yango University, Fuzhou 350015, China; [EMAIL_ADDRESS] (S.W. ); [EMAIL_ADDRESS] (Y.G. )1 College of Civil Engineering, Fuzhou University, Fuzhou 350108, China; [EMAIL_ADDRESS] (S.S.); [EMAIL_ADDRESS] (H.Z. )1 College of Civil Engineering, Yango University, Fuzhou 350015, China; [EMAIL_ADDRESS] (S.W. ); [EMAIL_ADDRESS] (Y.G. )1 College of  
mature construction techniques, and good strengthening effects, they are time-consuming, expensive, and traffic-disrupting because of the necessary construction of cofferdams, which are used for drainage before strengthening works. Consequently, increasing attention has been paid to undrained strengthening technology recently. A number of undrained strengthening techniques have been developed and applied to practical engineering in the past decade, such as the jacket strengthening method [6], FRP underwater strengthening method [7; 8], and precast concrete segment assembly method (PCSAM) [9]. These methods are economical, fast, and traffic-friendly compared with conventional methods, but also have some fatal deficiencies. For instance, the jacket strengthening method can greatly improve the durability of components but piers cannot be wrapped in fiber sleeves in deep water, which leads to strengthening failure. For the FRP underwater strengthening method, although the underwater strengthening effect is good, the empty gap generally occurs in the interface between the FRP and components because of the ineliminable water. As a result, this method tends to fail when the piers are submerged in water for a long time after strengthening. Additionally, the diving operation involves high costs, safety risks, and slow progress in deep water and under certain water pressure and flow rates. On the contrary, the PCSAM first uses precast concrete segments to wrap the components, then the segments are connected into the sleeve using wire ropes, and finally the interspace between the sleeve and the components is filled with the filling material to achieve undrained strengthening. The PCSAM can be used to strengthen the components in deep water. This approach has many advantages, including the simple construction method, reliable construction quality, short construction period, and low cost. However, there are still some problems with the PCSAM, such as the large prestress loss and poor durability of the wire ropes, poor accuracy and connection performance of the sleeves, large strength loss of the filling material, and uncertain bonding properties between the filled concrete and sleeves. As a consequence, there is an urgent need to solve the problems existing in the PCSAM and to develop a new strengthening method that can better serve in the reinforcement of damaged components. Based on the PCSAM, this paper proposes a new undrained strengthening method named the improved precast concrete segments assembly method (IPCSAM), which takes advantage of three theoretical reinforcement techniques, namely the increasing section method, outer sleeve method, and prestressing method. The IPCSAM proposed in this paper not only uses self-stressed anti-washout underwater concrete (SSAWC) as the filling material, but also improves the connection of the segment sleeve, which is referred to as the shield lining segment. The SSAWC, as the filled concrete, can not only cut down the strength loss of the underwater concrete [10; 11; 12], but can also increase the bonding strength between the filled concrete and the sleeves [13]. On the one hand, due to the additional appropriate expansion agent added to the SSAWC compared with the AWC, the concrete becomes denser and the self-stress makes the bond between the sleeve and the filled concrete stronger. On the other hand, the shield lining segments have high precision in prefabrication [14], good connection effects [15], and good durability [16].