Seipp Construction

HIGHLY COMMENDED

CATEGORY 1A

CATEGORY 1A: Projects with a value of less than $5 million (Company turnover less than $10 million)

PROJECT: Beachville Road Eastern Seawall Rehabilitation. CONTRACTOR: Seipp Construction

Working below sea level

During the Christchurch earthquakes the area around Beachville Road suffered lateral spreading and liquefaction. Impacted structures included the Beachville Road eastern seawall with sections of the wall collapsing during the initial shaking and sinking due to the increased weight loading.

The wall was initially constructed to prevent erosion along the coast, and to protect an area enjoyed by the public for recreational purposes and housing situated on the western side of the road. The seawall forms a part of the Christchurch Coastal Pathway.

The project to reconstruct the seawall along a halfkilometre section was awarded to Seipp Construction (formerly Connell Contractors South) based on its submission of an innovative construction methodology and ability to provide the specialised plant and expertise associated with working in a tidal marine environment.

Work involved removing the damaged seawall, stabilising the shoreline and constructing the new seawall. This required significant work below sea level – both for the removal of the damaged wall and to construct the lower sections of the new structure.

The new 500-metre seawall was built in layers and required sequential logistical scoping of the project. This included ‘trimming’ the seabed to the design profile, the placement of reno-mattresses to prevent under-scouring by the sea, construction of the new seawall core – which was done in 23 metre to 35 metre sections, with each section constructed inside a ‘dry-cell’ created by sheet piling and dewatering. Revetment was achieved using multiple layers of geotextile material, gravel and rock. Ethically designed precast panels were also installed along the top of the wall.

Additional complexities encountered in the project included the poor visibility while working four metres under water. As components of the wall had to be completed with a high degree of accuracy to ensure levels and slopes adhered to the design specifications a DGPS survey system was installed in the main excavator to enable the exact placement of rock.

Safety was paramount and a process of ‘de-risking’ the physical hazards was observed at all times.

The client was extremely pleased with the result, citing it as an outstanding and brilliant piece of engineering that surpassed the Council’s requirements. l