## 5 Conclusions  
This study sets out to improve the PCSAM with the SSAWC and the LCSS. Initially, the strengthening effects of the above two improvement measures on the bearing capacity of the strengthened specimens were verified using an axial compression test. Then, the extended parameter analyses were performed by establishing the numerical models. Finally, the calculation formula for the axial compression bearing capacity of the strengthened specimens was established. The following conclusions were made:  
1. The IPCSAM has good strengthening effects on underwater pier strengthening structures without causing undraining. Compared with the unreinforced column, the axial compression bearing capacity and peak strain of specimens strengthened by the IPCSAM increased by 90-130% and 30-60%, respectively. This indicates that the bearing capacity and ductility of the strengthened specimens were considerably improved;
2. As the filling material, the SSAWC can reduce losses in underwater strength in concrete and can produce expansion and self-stress. The self-stress not only improves the bond strength between the filled concrete and the adjacent member, but also provides a preloading effect on the column, which can improve the strength and ultimate strain of the concrete. Compared with the specimen strengthened by AWC, the bearing capacity of the specimen strengthened by the SSAWC increased by 18% and the strengthening efficiency increased from 0.71 to 0.86;  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Name**} & \multirow{2}{*}{ \begin{tabular}{c} **BCT(S) \({}^{\star 1}\)** \\ **(kN)** \\ \end{tabular}  } & \begin{tabular}{c} **ACSC of** \\ **Column** \\ **(kN)** \\ \end{tabular}  & \begin{tabular}{c} **Concrete** \\ **Coucretes** \\ **Strength** \\ **(kN)** \\ \end{tabular}  & \ \begin{tabular}{c} **Concrete** \\ **Strength** \\ **(kN)** \\ \end{tabular}  &
\begin{tabular}{c} **Coucretes** \\ **Strength** \\ **(kN)3. The LCSS improvement caused by the shield lining showed reliable connection performance, which remained in good condition when the specimen was broken. In the test, the LCSS showed good integrity and confinement, which could increase the bearing capacity of a specimen. Compared with the PCSAM, the strengthening efficiency of the specimen strengthened by the IPCSAM increased from 0.65 to 0.71; 4. The strength of the filled concrete, the strength of the LCSS concrete, and the self-stress were the key parameters affecting the bearing capacity of the specimens. With the increase in filled concrete strength, the LCSS strength, self-stress, and bearing capacity increased accordingly; 5. The calculation formula for the bearing capacity of the strengthened components has been proposed. The findings from this study show that the formula has good applicability and provides a theoretical design basis for the application of the IPCSAM. In addition, preparing the specimens requires a large number of steel molds and careful concrete curing, which takes a lot of time. Considering the time needed and the restrictions on research and development funds, only a small number of specimens were tested and a numerical simulation was conducted. As a consequence, the above-mentioned conclusions and remarks are only validated by limited experimental and simulation results. More experimental data and numerical simulations are needed to validate the proposed formulas in the future. Conceptualization, S.J. and S.W. ; methodology, S.J. and S.W. ; software, S.W. and H.Z. ; validation, S.W. and Y.G. ; formal analysis, S.W. ; investigation, S.W. ; resources, S.W. and S.J. ; data curation, S.W. and H.Z. ; writing--original draft preparation, S.W. and Y.G. ; writing--review and editing, S.J. and S.S.; visualization, S.W. ; supervision, S.S.; project administration, S.J. ; funding acquisition, S.J. All authors have read and agreed to the published version of the manuscript. This work was funded by the National 13 th Five-Year Research Program of China (Grant No.