Client: Barratt David Wilson Southern
Date: 2015-16 (30 Weeks)
Nature of Works: Decommissioning, soil remediation, site re-engineering & restoration
Contract Value: £1.9m NEC Option A (Lump Sum) Contract
The former Cane Hill Hospital is being redeveloped to a prestigious residential housing scheme by Barratt David Wilson (BDW) in partnership with the Homes & Communities Agency and the Greater London Authority. The central 10Ha portion of the former hospital site presented a variety of contamination & geotechnical issues, including 2nr former hospital landfills containing asbestos containing materials (ACM’s), site-wide metal, PAH and trace asbestos contamination within shallow fill, unconsolidated made ground disturbed by previous demolition works, several areas of Japanese Knotweed infestation as well as significant remnant in-ground obstructions. Additional areas of concern were identified beyond the main remediation area, including backfill materials containing asbestos insulation board fragments, additional Japanese Knotweed stands, service tunnels and remnant foundations – these had to be addressed in parallel to the main remediation programme to enable the first phase of construction.
Soilfix developed a materials management based remediation strategy in conjunction with RSK Environment acting on behalf of Barratt, to provide a more cost effective and sustainable solution, all in accordance with a Materials Management Plan (MMP) fully in accordance with CL:AIRE Code of Practice (CoP). 13,000m3 of Landfill materials were excavated, screened and sorted following primary controlled removal of both Japanese Knotweed rhizomes and notifiable ACM’s, prior to re-engineering to form a raised development platform and restored amenity area. The development platform required comprehensive slope engineering using geo-grid reinforcement to cement stabilised soils.
The main central hospital area was subjected to targeted obstructions removal, excavation and screening of shallow granular fill to segregate contaminated fines, high-energy impact compaction (HEIC) treatment of underlying made ground soils prior to re-grading and capping with site-won crushed materials.
Japanese Knotweed soils, following hand-picking to remove bulk rhizomes, were encapsulated at depth below open space areas in two separate “cells”, and surrounded by a copper-woven root barrier.
Soilfix also carried out various enabling works additional to the Lump Sum contract, including decontamination of lagged pipework in ducts, ductwork and remnant obstructions removal, archaeological investigation and reinstatements.
In spite of numerous unforeseen circumstances encountered during the project, Soilfix completed all works on time and on budget. Of the total 49,500m3 materials subjected to excavation, only 600m3 of gross contaminated / unsuitable material required disposal off-site, resulting in almost 99% materials recovery achieved.
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