London

Deptford Creek
Deptford Creek is a tributary of the Thames in London inside the Thames Barrier. In order to protect an estimated 33000 households from flooding, the Environment Agency identified five Wharves along Deptford Creek for immediate replacement. Existing anchored timber pile structures were assessed to be reaching a stage where failure was imminent. The five identified locations were Kent Wharf, Ash’s Wharf, Thanet Wharf, Hilton’s Wharf and Saxon Wharf.

About The Project
At the highest frontage the 109m long Hilton’s Wharf has a retained face of 7m. Future development plans for the site precluded the use of permanent anchors to support the new wall and so an innovative solution facilitating a composite wall system (propped structure) was engineered by Jacobs / Volker Stevin.
The new wall was to have a 100 year design life and was to embrace the objectives of the Biodiversity Action Plan. The solution consists of a steel sheet pile wall made of around 1040tonnes of AZ 41-700 in grade S430 GP steel grade, and in 16.5m up to 17.5m lengths. These are supported by a row of 12m long 305x223 HP bearing piles driven at a 10 degree rake in front of the sheet pile wall, with timber planking spanning between each HP pile.
A mass concrete block was then poured between the sheet piles and HP piles lines down to the excavated depth, exposing the gravel layer, such that the structure acted in unison. The top of the concrete block level was Mean High Water Neap (MHWN) level such that the planting area above could offer maximized value of environmental habitat.
The construction of this innovative “composite cantilever” sheet pile wall presented its own challenges in that the working space was limited to only 10m behind the existing old walls which were in such poor state that they could not support construction surcharges. Besides, in some places the existing wall could not be subjected to vibration from conventional installation techniques.

