Challenges Faced in the Construction of 60M Deep Diaphragm Walls, with Hydraulic Grabs in Central London, England-Paper

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The Battersea Station Box, part of London’s Northern Line Extension, required 1.2 m-thick diaphragm walls up to 60 m deep. Alternate panels extended through London Clay, hard and variable Harwich Beds, and the Lambeth Group to found in dense Thanet Sand. Excavation through the deeper strata was much slower than planned, with severe grab wear and breakdowns complicating panel sequencing and concrete scheduling.<br /><br />The project team used spoil logging, grab instrumentation and time-and-motion analysis to map ground variability and establish excavation rates. Trials showed that a centrally located, cased pilot hole through each deep panel substantially improved grab performance by weakening the hard, confined strata. Average excavation rates rose from 0.3 to 2.9 m²/hour in the Harwich Beds and from 1.9–3.0 to 5.1 m²/hour in the Lambeth Group. More intensive preventive maintenance, informed by breakdown records, also reduced equipment downtime.<br /><br />Construction within a three-sided, 3 m-deep cofferdam created restricted access and complex vehicle movements. A purpose-built concrete discharge chute allowed deliveries from a higher level, reducing truck movements into the work area and supporting safe, efficient operations.<br /><br />The project also developed a bespoke frame to install 12 plunge columns in low-cutoff diaphragm wall panels, where conventional pile-based positioning methods could not be used. When one column exceeded verticality tolerance and failed checks for temporary loading, accurate as-built records and BIM enabled remedial strengthening to be designed before bulk excavation.<br /><br />Despite challenging ground, access constraints and tight installation tolerances, the diaphragm walls were completed on programme and budget, with no lost-time accidents. The project demonstrated the value of adapting excavation methods to ground conditions, systematic data collection, preventive maintenance and BIM-supported problem solving.

Keywords

Battersea Station Box

Northern Line Extension

diaphragm walls

London Clay

Harwich Beds

Lambeth Group

Thanet Sand

pilot hole excavation

grab wear

BIM-supported construction