Client Project

Southgate

Bath, Somerset
Client

P J Carey

Project

Southgate Shopping Centre

Dewatering System
  • Deep Wells

Bath is a UNESCO World Heritage site famous as the site of Britain's only hot springs. Every day over one million litres of water at 46°c rises from deep below the city and flows through the Roman Baths to the river Avon.

The Southgate Bath development is only a few hundred metres from the site of the baths and has been carefully designed to blend in with the existing Georgian architecture using Bath Stone cladding on much of the project.

The project includes an underground car park with 860 spaces together with an underground delivery area for the retail units. This large basement area was constructed in a secant piled cofferdam roughly 80m wide and 160m long. The excavation was over 10m deep and there was concern that the underlying aquifer which feeds the thermal springs could cause the base of the excavation to heave. All excavations in Bath greater than 5m require consent from Bath and North East Somerset Council before starting, and although the initial site investigation showed that the risk of encountering artesian water was low, the dewatering system was designed to cope with this. The wells could be sealed at any point during the drilling or pumping to prevent artesian flow, and they were designed so that they could be effectively sealed on completion of the pumping.

Building The Bullring Birmingham

Construction At Southgate

The Result

Once the dewatering system was installed several weeks were spent test pumping the system in order to assess the effect on the area outside the cofferdam and any possible effect on the thermal springs. There were concerns that excessive pumping would reduce the flows to the main spring and therefore we installed a control system using pressure sensors located in each pumping well and two observation wells which ensured that the water pressure below the cofferdam remained at a level of 7.5m below ground level, which had been calculated as the maximum level possible. This enabled us to accurately maintain the minimum possible drawdown so allowing the excavation to take place safely whilst still safeguarding the thermal springs.

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