London Underground Hainault Embankment Widening Retaining Wall Solution

The London Underground Central Line at Hainault, originally part of the Great Eastern Railway’s Fairlop Loop established in 1903, has been operational in its current form since 1948. At this location, the railway runs above ground on an embankment, presenting unique engineering and maintenance challenges.

A project requirement to widen the embankment crest was introduced to provide safe access alongside the operational tracks. However, maintaining the existing embankment stability required preserving a 2:1 slope gradient. Achieving the required widening under these constraints would have necessitated extending the toe of the embankment outward.

This posed a significant issue for the rail operator, Metronet BCV Ltd, as it would require the acquisition of additional land adjacent to the railway corridor. Given the cost, logistical complexity, and proximity to residential properties, land purchase was not a viable option. A more efficient embankment stabilisation solution was therefore required—one that could enable widening works without increasing the footprint of the structure or disrupting railway operations.

To overcome these challenges, Cementation Foundations Skanska Ltd, in partnership with geotechnical consultants Mott MacDonald Ltd, collaborated with Maccaferri Ltd to develop an innovative retaining wall solution tailored to the constraints of the site.

Key considerations included limited site access, the proximity of residential areas, and the requirement to keep the Central Line fully operational throughout construction. These factors ruled out traditional heavy construction methods and demanded a solution that could be installed efficiently within a confined working area.

The adopted approach involved the construction of a segmental retaining wall system to support the widened embankment. The existing slope was locally reprofiled and steepened to approximately 45 degrees, creating sufficient space for construction without extending beyond the existing boundary. A horizontal working platform was then formed within the embankment, enabling safe and controlled installation.

This reinforced soil retaining structure allowed the embankment crest to be widened without moving the toe of the slope, thereby eliminating the need for additional land acquisition. The solution provided long-term stability, minimised environmental and community impact, and ensured uninterrupted operation of the London Underground Central Line during the works.