South Australia & NT Chapter

Geotechnical Engineering Aspects of the Bath CSO Project, England

Matthew Duthy

In this talk, Matthew Duthy presented a case study of a major civil engineering project with which he was involved while working for Binnie Black & Veatch plc (BB&V) in the United Kingdom. The Bath Combined Sewer Overflow (CSO) Project is an ambitious project to improve the performance of the sewerage system in Bath, England. Driven by regulatory requirements to improve water quality, Wessex Water proposed a major upgrading of sewage collection and treatment west of Bath. The upgrading will involve the need for significantly more hydraulic capacity in the sewerage system, in the form of large underground tunnels and/or storage tanks. One of the main complications and risks for the project is that the proposed works are adjacent to the World Heritage listed Bath city centre with its unique hot thermal springs. It is crucial that the works do not have an adverse impact on the hot springs. In order to mitigate these risks, a comprehensive geotechnical site investigation was commissioned by Wessex Water. BB&V were retained by Wessex Water to act as their lead design consultant (owners engineer) for the scheme, and Matthew Duthy acted as the Resident Engineer for the site investigation. Based on the results of the site investigation, Wessex Water commissioned a comprehensive feasibility study from each of three design and construct civil engineering consortia, in order to identify the preferred elements and layout for construction of the scheme. The talk discussed the regulatory, contractual and technical background to the project and describe the geology and hydrogeology of Bath. The site investigation was outlined, with a particular emphasis on the strategies adopted for obtaining key ground information while safeguarding the integrity of the hot springs. Geotechnical aspects of the feasibility studies by the design and construct consortia were outlined, along with the process of BB&V’s assessment of geotechnical aspects of each consortia’s submission. Finally, proposed further works for the scheme were outlined. Dr Duthy was educated at Adelaide University and will be well known to many of the SA AGS membership, from his time on the committee (as secretary) prior to his accepting a position with Binnie Black & Veatch plc, in their Surrey office (outside London) in October 1998. Matthew returned to Adelaide in October 2001, and took up his current position as senior geotechnical engineer with URS, and is again active on the AGS committee.

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