Civil Engineering May 2022 | Vol 30 No 4

Civil Engineering May 2022 27 Sheetpiling, which could only com- mence after removing all the failed wall backfill, was done using a vibrohammer fitted to an excavator (see Figure 10). Sheetpiles were installed in time to prevent scouring beneath the CCT sewer (see Figure 11). CCTV camera inspec- tion inside the sewer and inspection of the concrete afterwards confirmed no damage or movement had occurred to the sewer. Outer sheetpiles were installed after rotating the old retaining wall units forward by 90° with the help of the sea scouring in front (see Figure 12). The wall base was upright and formed a barrier to waves. The sand within the cofferdam was excavated using an excavator at Erf 234 (see Figure 13). Excavation was done more efficiently at Erf 636 from lessons learnt at Erf 234 by using an excavator to remove the bulk of the sand material and then continuously filling the cofferdam with seawater by pumping and dredging the sand simultaneously down to bedrock using another pump. The diver dredging and mass concrete foundation to bedrock was done on the same day for Erf 636 (see Figure 14). Concrete was continu- ously pumped from readymix trucks at Ons Huisie. Limited space at the Small Bay Play Park was used as the contractor’s site camp. As access to the site was from the beach, placing of concrete was done by an excavator conveying concrete across the beach in front of the play park in a hopper from readymix trucks discharging concrete in Pelegrini road for Erf 234. The steel cofferdam made construc- tion of the insitu concrete foundation onto uneven bedrock in an active tidal zone and below mean sea level possible. PROJECT STATUS As soon as the seawall construction work was completed at Erf 234 in September 2018, work commenced at Erf 636. This ensured that the site establishment remained in place for the work at Erf 636. The Seawall at Erf 636 was completed in January 2019 (see Figures 15, 16 and 17). Construction of the new seawall on the two adjacent properties, one after the other, allowed the mass concrete founda- tion to effectively be continuous across the erf boundary, leaving no weak points for the sea to erode. PROJECT CONCLUSION The seawalls were successfully con- structed to the design specifications in difficult conditions, and the beach and Figure 12 Sheetpiles against sewer concrete encasement and outer sheetpiles in place to form a cofferdam at Erf 234. Outer sheetpiles could only be installed after rotating the old concrete walls forward Figure 13 Excavation to bedrock in cofferdam at Erf 234 Figure 14 Concrete casting inside the sheetpile cofferdam at Erf 636 in October 2018