Steam Pipe Line Tunnel

Twenty four expansion pits were built into the East Perth Power Station’s steam pipe tunnel, to ensure safety and maintenance points along the long underground line. Particularly as the pipe carried steam of up to nearly 315°C, it constantly expanded and contracted as it cycled between hot and cold temperatures. Without somewhere for this movement to go, the pipe would have pushed against the tunnel walls, cracked welds or even damaged the concrete structure around it.

 

Expansion pits solved this problem by creating wider, accessible sections along the route where the pipe was fitted with bends, loops or sliding supports that allowed it to move safely without building up dangerous stress. These pits also contained anchors to hold the pipe firmly in place on either side so the shifting happened only where engineers intended. They doubled as practical work areas too, which were large enough for workers to climb down into to inspect the pipe, check insulation, maintain steam traps, drain condensate and deal with issues like leaks or water hammer that sometimes affected the system.

 

During construction, the pits also acted as insertion points where lengths of pipe could be lowered in, aligned and welded.

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There were also 24 anchor pits built along the tunnel.

 

Measurements

Eight different expansion pit sizes ranged from 41’ 4” x 29’ 10” down to 22’ 10” x 17’ 10”.

 

The number six expansion pit (photographed) is the third biggest size with 37’ 4” x 27’ 4”.

 

Average measurements for the steam pipe line:

• 8-inch concrete floor and wall thickness

• 3 to 4 feet internal tunnel width

 

Timber Piles

To support the steam pipe tunnel running between the East Perth Power Station and Royal Perth Hospital, engineers installed timber piles under the concrete floor. Each pile was 3 feet tall with a 5×5-inch square cross-section and they were arranged in a regular grid to stabilise the soft, moisture-affected riverbank soils the tunnel passed through.

 

Rather than acting as deep foundation piles, these smaller posts were designed to stiffen the upper layers of the ground, evenly spread the tunnel’s weight and prevent it from gradually sinking or shifting over time.

 

Once the piles were driven into the soil until the stable ground was reached, the tops of the timber were levelled off and the concrete tunnel floor was poured directly over them, creating a solid and stable base for the entire length of the tunnel.