*2.1. SSAWC Preparation*

The use of self-stressed anti-washout underwater concrete (SSAWC) is one of the key strategies for implementing the IPCSAM, because the filling material connects the components and segment sleeves and directly affects the mechanical properties of the strengthened components. Wu and Jiang [10] developed the SSAWC and achieved good performance. The compressive strength ratio in water compared to air for the SSAWC increased from 0.8 to 0.92, indicating that the strength loss of the filling material was significantly reduced. The restrained expansion ratio at 14 days for SSAWC could reach 0.027–0.053%, while the self-stress generated by expansion would be beneficial to increasing the bond strength [13]. Meanwhile, the experiments carried out by García-Calvo [12] showed that the underwater environment was more beneficial to the self-stress development of the SSAWC for piers and columns.

According to the mix ratio of the SSAWC shown in Table 1 and proposed by Wu [10], performance verification tests for the C30 SSAWC were carried out. The 42.5 *N* normal Portland cement from Fujian Cement Inc. (Fujian, China), a fiber-type anti-dispersion agent named SBTNDA, and the HME-III low-alkali concrete expansive agent produced by the Jiangsu Soubotte Company (Nanjing, China) were chosen. A polycarboxylate superplasticizer was employed in these tests based on experimental results from Khayat [21] and Oliveira [22]. Here, 5~20 mm of continuous-grade gravel was used. The density, crushed index, needle content, and sediment content of the gravel were 2.65 t/m3, 7.3%, 2%, and 0.2%, respectively. Good Fujian River sand was used, the fineness modulus, sediment content, and density of which were 2.89, 0.6%, and 2.64 t/m3, respectively. The test results showed that the C30 SSAWC (Table 2) had a higher elastic modulus and underwater strength compared with the AWC and the expansibility of the SSAWC could be easily observed.





#### *2.2. LCSS Preparation*

The use of a lining concrete segment sleeve (LCSS) is another key strategy for implementing the IPCSAM, as the sleeve can be used as formwork in the construction process and as a part of the strengthened piers to bear partial loads, in addition to being a limitation that makes the SSAWC produce self-stress. Huang [14] studied the precast technology used for the shield lining segments and found that the prefabrication precision could be

improved by controlling the working procedures to achieve assembly error within 2 mm for the inner ring segments. In the experiments conducted by Liu [15], the failure of the shield tunnel linings was caused by failure of the joints, while the bearing capacity of the joints was improved using strengthening bolts. The study by Meng [16] showed that the durability of the shield lining segment could be improved by adding steel or propylene fibers or steel bars into the concrete. Therefore, the LCSS was designed and prepared with the characteristics and theory of shield lining segments.

The LCSS design was divided into structural and connection designs. The structural design determined the preassembly form and segment dimensions. The LCSS was divided into two parts, namely the standard segments and adjusting segment; the sleeve ring consisted of three standard segments and one adjusting segment, as well as a setting rabbet between the segments. The dimensions of the segment were determined based on the self-stress, load, thickness of the concrete cover, diameter of the PVC pipe, and the construction technique. The structure of the LCSS is presented in Figure 1, and the segment dimensions of the specimens are designed as follows: inner diameter of 165 mm, outer diameter of 205 mm, thickness of 40 mm, height of 170 mm. The connection for the LCSS was designed in the same way as the connection for the shield lining segments. Specifically, for circumferential connection of the segments, the holes for fixing bolts were reserved through the pre-embedded PVC pipes and then the curved bolts and triangular pad were utilized to connect the segments. Regarding the longitudinal connection of the segment, the hole was also reserved first, then the long bolts and nuts were used to connect the segments. In this test, the diameter of the PVC pipe was 16 mm and the diameters of the circumferential and longitudinal bolts were 6 mm and 8 mm, respectively. Three circumferential connections were arranged along the longitudinal equal spacing of each segment ring, and 10 longitudinal connections were arranged at equal intervals along the circumference; the connections of the segments are shown in Figure 1. The prefabricated mold of the LCSS was designed and is shown in Figure 2. The size of the segments and location of the PVC pipe complied with the requirements found in [14].

**Figure 1.** Structure and connection of the LCSS. (**a**) Segment ring; (**b**) Standard block; (**c**) Adjusting block; (**d**) Circumferential connection.

**Figure 2.** The LCSS and mold. (**a**) Segments; (**b**) Sleeve; (**c**) Mold of segments.
