Victor Harbor Jetty (Granite Island Causeway) Demolition

Introduction

Incon was engaged to provide structural engineering design and verification for demolition works of the Granite Island Causeway at Victor Harbour. The project required the development of safe and efficient lifting systems to dismantle heavy timber deck modules while maintaining control over structural behaviour and construction risks.

Project
description

The demolition methodology involved lifting and removing modular sections of the timber causeway deck, each measuring approximately:

4.1m wide x 6.0m long
Weighing up to ~5.2 tonnes per module

The approach utilised:

Twin gantry lifting systems
Custom-designed trolley frames running on existing rail tracks
Threaded rod and plate lifting connections through timber joists
Modular transport and staged removal of deck sections

Challenge

Large timber deck sections required controlled lifting and transport across an existing structure exposed to marine conditions.
Timber joists (~220mm width) introduced limitations on:

Edge distances for drilling
Bearing capacity under lifting plates
Risk of splitting during load application

Initial propping systems (SYS15) were found to be near capacity under combined loading, requiring reassessment.
Independent review identified:

Missing combined compression + bending checks
Potential local failure at connection plates
Need for upgraded structural capacity

Solution

Incon delivered a refined and robust engineering solution addressing lifting design, connection detailing, and temporary works capacity:

Engineered threaded rod and plate system:

Ensured minimum 75mm edge distance to prevent timber breakout
Verified bearing capacity of 190x190 plate interface with joists

Designed and assessed trolley systems to:

Support up to 3T+ loading scenarios per unit
Enable movement along existing track infrastructure
Maintain stability during transport of lifted modules

Upgraded from SYS15 to SYS30 propping system to:

Address high utilisation under combined loading
Provide adequate capacity for bending + compression checks
Improve overall safety margin

Key Engineering Value Delivered

Enabled safe and controlled demolition of heavy structural modules
Eliminated risk of timber failure during lifting operations
Delivered engineered lifting and transport system tailored to site constraints
Successfully addressed third-party engineering review requirements
Improved temporary works safety through system optimisation
Supported efficient staged demolition with minimal disruption

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