Wharf and Embankment Rehabilitation

Heavy seas and extreme tidal activity had eroded the backfill out from under the wharf slab through the rock seawall, making the wharf unsafe for bearing the heavy loadings. Proximity to the Great Barrier Reef World Heritage Area demanded an environmentally sensitive solution to stabilise the seabed and seawall embankment. In just 9 days, Mainmark re-supported the wharf slab in order to safely bear the typical loadings of 90 tonnes or more.

The objectives were:

1. To seal the seawall to prevent water penetration and to stop concrete loss during the void filling,

2. to consolidate the sand bed and re-support the rock seawall,

3. to fill small voids under the slab and around the edge of the mass void fill (330m3),

4. and to ensure full support and weight-loading of the wharf slab, to mitigate any flexing during crane operations.

Mainmark utilised an innovative range of materials and application technologies in 3 phases: Firstly, Uretek polyurethane grout was injected into the sandy base of the toe of the rock wall embankments. This stabilised the sands and silts of the seabed. Secondly, the rocks forming the seawall embankments were agglomerated by injection of dual component resin within the voided matrix of the walls. This material is hydrophobic and completely environmentally inert. The injected material expanded, filling voids, and adhered to the rocks, agglomerating them and binding them together, and so substantially improving the structure of the embankments. Thirdly, approximately 330m3 of voids beneath the wharf slab area were filled and the slab was undersealed and completely re-supported. Resin was used also for this process, being injected via 16mm Ø holes in a grid pattern covering 90m2. The area was preloaded with the wharf crane. After injection, resupport of the whole area was confirmed by laser level indicating a uniform lift of 3mm – 5mm.

The wharf area seabed and the seawall embankment were stabilised. The weight bearing capacity of the stabilised wharf slab was completely restored. The Mainmark technology proved very cost-effective compared with complete removal and replacement. The client’s managers were extremely happy with the end result and the professional approach by Mainmark and the attending crews.