Project: Victorian sewer repair
Client: Wessex Water
An impressive excavation to upgrade a Victorian sewerage system proved to be more complicated than usual for client Wessex Water. The 4-metre-deep trench was excavated by hand to the rear of one of Bristol’s historic landmarks – the Louisiana Public House.
The Louisiana was built to cater for travellers brought to the area by the construction of the Basin, part of the Floating Harbour. Fast forward 200 years and the Louisiana is now an iconic music venue hosting performances from legendary musicians.
The purpose of the excavation was to repair a collapsed sewer. Combined foul and storm drains presents several issues; as the tide rolls in the pipeline system is filled with deposits of debris causing blockages and floods. Client Wessex Water use a 360-degree camera to determine the location of problems within the pipeline.
The temporary works design had to consider several hazards in the proximity of the excavation. The location was surrounded by stepped ground levels with up to two metre height difference. These differences in levels were separated with thick brick walls up to 5 metres high. Foundation loads from the existing Louisiana building had to be considered being located within metres of the excavation location.
Nigel Phan, MGF Design Engineer explained,
“The limited accessibility and dimensions of the excavation presented various constraints. There were issues with access, egress and buildability that had to be overcome in such a small but relatively deep excavation.”
The design specified 7 no. MGF’s 2.5m medium duty aluminium waler frames complete with hydraulic struts and end protection struts. Two levels of frame locations were twinned and 4m long standard trench sheets specified. There was no access for an excavator so the lightweight aluminium walers and sheets was particularly beneficial for manual handling.
The 2.5m x 1.5m excavation was hand dug through granular made ground and completed in an impressive time by sub-contractor Lynwood Civil Engineering taking just 4 days.
Labourers exposed a brick chamber after digging to the planned 4 metres. An extra metre to the sewer floor was identified. Inspection of the brick course was essential to determine if additional temporary works would be required to support the sewer. This was not required, and the works continued.
Kevin Martin, Sales Manager for the South-West region said,
“MGF have a great relationship with Wessex Water. There is a valued and uniform understanding which helps get awkward jobs like this completed safely and within a reasonable timescale.”