The O’Shannassy Reservoir is a critical part of Melbourne Water’s network of dams and reservoirs, delivering drinking water to Melbourne.
The objective of this project was to address reservoir safety for operation and maintenance, following regular dam safety inspections. Original penstock designs were dismissed for this project due to the power that would be required to connect an electric actuator.
AWMA were engaged by the John Holland KBR JV to supply a customized isolation bulkhead and lifting frame for the O’Shannassy Reservoir Intake Pipe.
A single piece bulkhead was custom designed to cater for insertion and removal under hydrostatically balanced conditions (ie; no flow). The bulkhead isolates an aperture of 1.6m diameter and was designed to accommodate 18m of on-seating head pressure. Grade 2205 duplex stainless steel materials were selected to accommodate the nominated design loads.
For most bulkhead applications the guide rails are integral to the sealing frame. The nature of the intake shaft at O’Shannassy Reservoir did not allow for the standard frame arrangement. This instigated AWMA to design an innovative guide rail system that was independent of the sealing frame. The bulkhead deployment and retrieval process was to be safely managed without the need for divers.
The intake at O’Shannassy Reservoir is off-centre within the shaft. To accommodate this the AWMA design team developed a solution to incorporate extendable arms within the bulkhead, allowing operators to effectively and accurately position the bulkhead, from the surface, despite it being 16m underwater. This was achieved using a bespoke AWMA Self-Engaging Lifting Frame, also featuring outrigger style extendable guide arms.
The Self-Engaging Lifting Frame is specifically designed to safely lower the bulkhead gate into position before automatically disengaging, to be returned to the surface and into AWMA Storage Racks. When the bulkhead is to be retrieved, the Self-Engaging Lifting Frame is set to retrieval mode, lowered into the guides, it automatically locks onto the bulkhead gate and, under flow, raises the bulkhead to the surface. All of this is achieved from above the shaft without the need for divers or operator intervention.
To address risks associated with misalignment of the guide and sealing frames, AWMA assisted the JHKBR JV by providing an Installation Supervision and certification Service to ensure all equipment was installed per the design intent.
