Drift-filled hollows in Battersea: investigation of the structure and geology along the route of the Northern Line Extension, London

Abstract

Drift filled hollows (DFHs) are a major subsurface hazard for engineering in London. They are characterised by a steeply inclined cone-shaped hollow into (sometimes through) the London Clay Formation, filled with unconsolidated fine to coarse-grained drift and often covered by terrace gravels, making them difficult to identify at the surface. Their origin remains uncertain but most likely formed towards the end of glacial epochs by meltwater scouring, perhaps of collapsed pingos. Usually associated with tributaries to the Thames, DFHs are particularly prevalent in the Battersea area, through which the Northern Line Extension (NLE) is to be built. This study uses 283 public borehole records and site reports to build a 3D geological ground model of two known DFHs in the Battersea area to develop a more complete understanding of their origin. We show that DFHs are likely older than previously assumed, dating from the end Anglian [MIS 12], ~300 ka ago, before the deposition of the River Terrace Deposits. The two DFHs modelled fall into distinct types: a small shallow DFH that is probably a purely scour feature in origin, and a larger, deeper DFH which probably formed by the scouring of a perhaps fault controlled pingo. It is unclear whether the faults controlled pingo formation passively by acting as a conduit for water, or in a more active sense by driving ground movements. Both DFHs represent a significant hazard for the NLE and require more detailed investigations to properly constrain their extent

Retrospective InSAR Analysis of East London during the Construction of the Lee Tunnel

“…Secondly, it is proximal to the Plaistow Graben fault zone (Figure 10), which is 750 m to the north-west and a suspected product of major fault linkage, implying the presence of an unmarked fault locally [31]. Thirdly, the north-east continuation of this boundary intersects the DFH at Newham Hospital and DFH's are postulated to have an association with faulting [35,38], since faults provide pathways for groundwater flow.…”

“…DFH's are a substantial hazard to tunnelling projects, often containing perched water leading to variable groundwater conditions, potential slumping, shearing of the sides and differential compaction of material [29,38]. Adjustments to the TBM may be required in response to such variable conditions, such as an increase in TBM thrust or a decrease in cutting wheel rotation speed [30].…”

Chapter 1 Introduction to Geological Hazards in the UK: Their Occurrence, Monitoring and Mitigation

“…Much work has been undertaken in London to further delineate the presence of these anomalous depressions in the London Clay. Various modes of formations of these features have been proposed, including simple scour, dissolution of the underlying chalk, valley bulging, frost heave, former ice wedges or thermokarst processes, or it has even been proposed that they are former pingo remnants (Banks et al 2015;Toms et al 2016;Griffiths & Giles 2017).…”

“…Newman et al 2013), and perched water tables (e.g. Toms et al 2016) can cause massive problems related to ground engineering, even when well understood and characterized.…”

Lessons for Sustainable Urban Development: Interplay of Construction, Groundwater Withdrawal, and Land Subsidence at Battersea, London

“…Thus, the case study of Battersea, London, holds significant relevance in the context of global urban development and retrofitting endeavours. With its rapid urbanisation and ongoing infrastructure projects like the Battersea Power Station redevelopment and the Northern Line Extension [14], it becomes crucial to comprehensively assess the effects of land subsidence, piling work, and groundwater abstraction. By studying the interplay of these factors in Battersea, valuable insights can be gained to inform wider urban development practices, foster resilience, and support the achievement of SDG 11 on a global scale.…”