Logging the Lambeth Group Upper Shelly Beds for the Thames Tideway Tunnel in London, UK: More than just “dark grey clay with shells”
Section snippets
The Lambeth Group Upper Shelly Beds
The Lambeth Group was deposited at the end of the Palaeocene and beginning of the Eocene epochs, approximately 54–56 million years ago (J. Skipper, pers comm., 2020), on the south western margin of a fault-controlled marine basin (in approximately the same position as the present-day North Sea), where relatively small-scale changes in sea level caused significant changes to the sediments deposited (Knox, 1996, Page and Skipper, 2000). The Upper Shelly Beds are at the top of the Lambeth Group
Thames Tideway Tunnel
The Thames Tideway Tunnel was implemented in the early 1990s under the (European Union) Urban Waste Water Treatment Directive to improve the water quality of the River Thames (Stride, 2019). It is currently under construction and will be a 25 km long, 7.2 m internal diameter storm water storage tunnel, extending west to east across London on a falling gradient of 1:890 and following the course of the River Thames through central London (Fig. 1). Construction is 30 m deep in Acton, west London,
Tideway Tunnel borehole investigation
Nearly 500 investigation boreholes were constructed for the Tideway Tunnel preconstruction geological model (Fig. 2). This was developed from the desk study conceptual model based on approximately 3000 archive borehole records held by the British Geological Survey (BGS) and Thames Water and augmented by a marine hydrographic and seismic survey (Newman and Hadlow, 2011). Most of the investigation boreholes were constructed using rotary coring techniques, with a high concentration around the
Construction geological logging
The Upper Shelly Beds were intersected by 3.2 km of the main tunnel profile and by five shafts, as well as the East and West TBM launch adits leading off the shaft at Kirtling Street; each 10 m in diameter and 37 m long (Fig. 8). In addition, a small trial pit was excavated in the shaft at Cremorne Wharf to reveal the extent of the Upper Shelly Beds beneath the final base level. This was undertaken only after thorough checks were made to ensure that the engineering design would not be
Geotechnical parameters and engineering behaviour
Despite their comparatively limited thickness, the Upper Shelly Beds have had a significant impact on construction where they have been encountered. In all of the shafts, a considerable and abrupt increase in the strength of the ground was experienced when passing from the London Clay Formation to the Top Shelly Clay Bed (the Harwich Formation, when present, was generally too thin to have any noticeable effect), typically resulting in a reduction in the rate of excavation by at least 50%.
Conclusions
Geological logging during construction of the Thames Tideway Tunnel has revealed a distinct and laterally continuous sequence of strata within the Lambeth Group Upper Shelly Beds beneath central London. This extends for over 4 km between the Albert Embankment and Cremorne Wharf sites. The sequence comprises discrete beds of typically dark grey clay, either with abundant white shells and strongly cemented shell coquinas, or with closely spaced partings and laminations of light grey silt or fine
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The author would like to convey thanks to Tideway and Jacobs for permission to publish this paper and to the FLO and BMB joint venture contractors for facilitating the excavations in which much of the field data has been collected. Special thanks go to Don Aldiss for his review of the manuscript and valuable advice and to Jackie Skipper for additional contributions. I am grateful to the two referees for their constructive comments. Thanks also go to Elena Granados, Alan Skarda and Roser Pujol
References (18)
Facies distribution in the Woolwich and Reading Beds of the London Basin, England
Proceedings of the Geologists’ Association
(1983)A mammal fauna from the Paleocene-Eocene Thermal Maximum of Croydon, London, UK
Proceedings of the Geologists’ Association
(2020)The stratigraphic framework for the Palaeogene successions of the London Basin, UK. Open Report OR/14/008
British Geological Survey, Keyworth
(2012)- et al.
Design of Primary lining (Diaphragm wall) at Kirtling Street Shaft for Thames Tideway Tunnel, Central Contract
Code of practice for site investigations
(1981)- et al.
Geology of London. Memoir of the British Geological Survey, Sheets 256 (North London), 257 (Romford), 270 (South London) and 271 (Dartford) (England and Wales)
(2004) - et al.
Engineering Geology of British Rocks and Soils – Lambeth Group
(2013) - et al.
Engineering in the Lambeth Group
(2004) - et al.
The Woolwich Formation of Croydon, S. London, UK: a PETM fauna and flora rediscovered
GNS Science Miscellaneous Series
(2009)
Cited by (4)
The 21st Glossop Lecture: engineering geology and the geoscience time machine
2023, Quarterly Journal of Engineering Geology and HydrogeologyConstruction geological logging of the Thames Tideway Tunnel beneath central London: unearthing the ground truth
2022, Quarterly Journal of Engineering Geology and HydrogeologyEffects of changing geology on the performance of a tunnel boring machine for the Thames Tideway Tunnel, London, UK
2022, Proceedings of the Institution of Civil Engineers: Geotechnical EngineeringGeological structures beneath the River Thames in London: findings from the Thames Tideway Tunnel investigations
2021, Quarterly Journal of Engineering Geology and Hydrogeology