Marine & Coastal Infrastructure
Seawall Construction & Coastal Protection Works
Client
Horton Coastal Engineering
Duration
February 2021 – December 2021
Location
Collaroy / Narrabeen NSW
Expertise
Bulk Earthworks and Land Remediation, Concrete and Retaining Structures, Marine Works, Pontoons and Seawalls
After the 2016 storm damaged the existing rock revetment and exposed beachfront properties to erosion, a seven‑metre‑high concrete structure was constructed to safeguard the shoreline.
Project Scope
- Excavation of existing rock boulders to remove obstructions to piling and anchoring
- Forming a temporary piling working platform and suitable bund
- Installation of secant piles (hard and soft piles) over a beach frontage, to reduce the risk of soil migration through the seawall and to provide support to the overlying retaining wall and preventing it overturning at times of beach scour
- Forming and pouring a reinforced concrete capping beam at the top of the piling
- Installation of anchors connecting to the capping beam
- Forming and pouring a reinforced concrete retaining wall, with mass concrete recessed stairs, above the capping beam
- Backfilling the seaward yards of the properties up to the seawall crest level
- Landscaping the disturbed areas of the seaward yards of the properties with lawn
Key Challenges
Stabilising the Site After Severe Coastal Storm Damage
A major storm in 2016 destroyed the existing rock revetment, leaving beachfront properties exposed to ongoing coastal erosion and structural risk. A new vertical concrete seawall was constructed, incorporating secant piles, anchors and a rock boulder toe to provide long‑term coastal protection and stabilise the shoreline.
Navigating Complex Ground Conditions for Secant Piling
The site contained large existing rock boulders that obstructed piling and anchoring works, making installation across the 200‑metre beach frontage challenging. Progressive excavation removed obstructions, while a temporary piling platform and bund were established to safely install hard and soft secant piles, ensuring structural integrity even during beach scour events.
Constructing a Durable Retaining Structure in a Sensitive Coastal Environment
The retaining wall required precise construction above the capping beam, along with integration of stairs, backfilling, and reinstatement of private seaward yards without disturbing the coastal setting. Our team formed and poured the reinforced concrete capping beam and wall, installed anchors for additional stability, carried out controlled backfilling to crest level, and completed landscaping to restore the seaward yards.
