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  Design of Primary lining (Diaphragm wall) at Kirtling Street Shaft for Thames Tideway Tunnel, Central Contract

  Thames Tideway Tunnel project is a new 25 km long combined sewage storage and transfer system beneath the River Thames in Central London currently under design and construction. Three design and build contracts have been awarded. The contract for the central section, the biggest and most challenging one, consists of 12.7 km of tunnel and 8 sites with deep inlet shafts and ancillary structures.The Kirtling Street Shaft, located near to Battersea within the London Borough of Wandsworth, is the largest in terms of diameter in the whole project. When complete, it will be approximately 60 m deep and have a 30 m internal diameter, employing the diaphragm wall construction method for its primary lining. This is the first shaft to be constructed within the central section and is strategically important as it serves as a TBM launch shaft from which two TBMs will be launched towards east and west respectively following the alignment of the River Thames. Due to the size and the depth of the shaft as well as the incorporation of two large temporary adits, which are going to facilitate the TBM launch, a diaphragm wall has been designed as the primary lining of the shaft.This paper provides an introduction to the Thames Tideway Tunnel project with focus on the design of the primary lining of the Kirtling Street Shaft, which is formed of 85.9 m deep diaphragm wall panels. This paper discusses the method of design employed for the shaft’s primary lining and presents the process and considerations behind some of the key decisions regarding the expected behaiviour of the structure. Furthermore, it outlines the design development of the shaft in different numerical packages, the evaluation of the modelling options and the parametric study that was undertaken during the detail design stage. Two numerical packages, namely PLAXIS 2D and PLAXIS 3D, were used to perform detailed analyses of the diaphragm walls and the results are presented in terms of horizontal displacements, structural forces and soil stresses. Tideway, Shaft, Diaphragm Wall, Numerical AnalysisThe primary objective of the Tideway scheme is to improve the ecology of the river Thames and comply with the EU’s Waste Water Treatment Directive (UWWTD). Therefore, the overflows of the current sewage system, located both on the south and north bank, will be intercepted prior to discharge into the river. The flows will be diverted in the 25 km long tunnel, which will run from Acton in West London to Abbey Mills Pumping Station in East London. The flow will then run to the Beckton Sewage Treatment Works via the Lee Tunnel (Jewell & O’Connor, 2012), the construction of which has already been completed in January 2016 (Ashenden & Garrett, 2016).

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