|
The Water's Lovely
The regeneration of the Vosper Thornycroft shipyard
in Southampton has brought the promise of the return of shipbuilding
to the River Itchen.
After more than five years of preparation, the regeneration
of the former Vosper Thornycroft (VT) shipyard in Southampton
is under way. The 12.5ha site, known as Woolston Riverside,
was purchased in 2003 by the South East of England Development
Agency (SEEDA).
Southampton City Council (SCC) and VT commissioned Tibbalds
Planning & Urban Design in 2002 to develop masterplanning
options to regenerate the area. The long held rivalry between
Portsmouth and Southampton ensured that people in Southampton,
having lost Vospers to Portsmouth, wanted every avenue explored
for keeping shipbuilding alive and well at Woolston.
Campbell Reith was commissioned to provide engineering advice
on the project in 2002 and was then appointed as engineering
consultants by VT and, subsequently, SEEDA.
Campbell Reith provided technical support to SEEDA during
the pre-purchase due diligence phase and throughout the master
planning works. This required the coordination of ground investigations,
archaeological and ecological investigations, hydrological
modelling, asbestos surveys, below-ground drainage surveys
and physical surveying of the existing buildings and river
frontage structures.
SEEDA's project manager David Holifield says that SEEDA's
aim was to "safeguard the deep water marine employment
in the northern part of the site, replace some of the jobs
lost when the VT shipyard closed, and promote the regeneration
of the Woolston area of Southampton by means of a high density
mixed use/ residential development".
SEEDA is undertaking the regeneration in conjunction with
two development partners. With Palmer Johnson, the northern
third of the site area is being developed for "super"
yacht manufacture. The remainder of the site is earmarked
for the construction of 1630 residential units by Crest Nicholson.
Ground investigation revealed extensive underground obstructions
and contamination by hydrocarbons, metals and asbestos.
It comprised 80 boreholes to depths up to 30m and nearly
180 trial pits, together with the monitoring of ground gas
and controlled waters and was carried out over four interlinked
phases. The total cost of the investigation was close to £450,000.
From the earliest stages Campbell Reith led negotiations
with the Environment Agency, SCC and Natural England about
how the development could best be integrated with the adjacent
mudflats that are designated a Special Protection Area (SPA)
under European habitat regulations, a Ramsar site, a Site
of Specific Scientific Interest and a Special Area of Conservation.
A Construction Environment Management Plan (CEMP) prepared
for the investigation was developed into the Environmental
Impact Assessment and Statement. Campbell Reith also provided
technical advice for the procurement and delivery of the £1M
demolition and asbestos removal contract.
The ground conditions are heavily influenced by previous
excavations on site that had removed River Terrace Gravels
for use as ballast on outward-bound ships. The geology comprises
Bracklesham Beds, overlain by a mantle of highly variable
fill, Alluvium with significant peat layers and some remnants
of the River Terrace Gravel. Artesian water was encountered
at depth in a number of the boreholes. The interpretation
of the complex stratigraphy was assisted by the use of GIS
and ground modelling software.
Potential contamination risks were identified to the adjacent
controlled water receptors and the proposed residential development.
As a result, quantitative risk assessments were completed
to determine the scope and objective of the remediation. Through
a process of negotiation, these were agreed with both SCC
and the Environment Agency
For controlled waters, risk assessments were combined with
a 12-month monitoring exercise using continuous multichannel
tubing that permitted several discrete water bodies beneath
the site to be monitored in parallel. In relation to human
health, remedial criteria were developed so soils from the
site could be retained after processing.
One of the guiding principles throughout the development
of the remedial contract has been to minimise the off-site
disposal of contaminated soils. To tackle this, site levels
were agreed with the rest of the design team and site-based
remedial solutions developed.
Of particular importance was the need to establish the most
appropriate and economic method of addressing asbestos contamination
in soil. This presented a challenge as it was necessary to
appraise not only the technical efficacy of the potential
treatment processes, but also the remedial targets and analytical
method for validation. Therefore, during 2007, a site trial
was implemented by remedial contractor HBR that examined the
ways in which asbestos materials could be sieved, screened
and washed from the soils.
In tandem, the Health and Safety Laboratory provided advice
and research on testing methods and an appropriate remediation
standard. These works facilitated a site-based remediation
without the general requirement for off-site soil disposal.
Sustainability was another driving factor in SEEDAs development
of the site. CampbellReith acted as structural engineer in
the assessment of building reuse potential and the removal
of overhead cranes to a SEEDA/Vesta wind turbine manufacturing
facility in East Cowes on the Isle of Wight.
Contract documents for the remediation and civil engineering
advanced works contract were issued in March 2008. The works
include demolition, structural repair, the construction of
new retaining walls, foundations and infrastructure, remediation
and earthworks. The contract was won by BAM Nuttall with remediation
subcontractor EDSR. Dust, noise and vibration monitoring is
being carried out in accordance with the developed CEMP because
of the numerous sensitive statutory designations associated
with the site.
As Southampton is short of deep water berthing available
to shipbuilders, the existing quayside structures towards
the north of the site are to be retained, repaired and reused
as part of the future marine development. CampbellReith, in
conjunction with the engineers for the proposed occupier,
designed the necessary repairs and strengthening works to
allow the construction and launching of super yachts up to
1 00m long. This included the construction of nearly 60 ductile
cast iron raking piles, 210mm in diameter, and a similar number
of 500mm diameter concrete vertical piles.
Many reinforced concrete-framed and masonry buildings, including
the massive "Fitting Out Trades Complex", are being
demolished together with hardstandings and shallow obstructions.
In some areas, foundations have been retained and recorded
for possible reuse, Demolition materials are being crushed
for reuse as engineered soils, and approximately 10,000m3
have been generated to date.
Site remodelling and excavations for remediation will result
in the excavation, screening, sorting and on site reuse of
approximately 200,00Om3 of validated site-won soil. It is
anticipated that only 500Om3 will have to be removed from
site. Significant changes in level adjacent to nearby Victoria
Road have required the construction of a 5m high contiguous
retaining wall around the north east corner. A rigorous monitoring
regime was put in place to ensure the stability and integrity
of an existing poor quality retaining wall at high level as
well as a Victorian sewer beneath the highway.
The water monitoring exercise confirmed the adequacy of natural
attenuation to address the risks presented by hydrocarbons
in both soils and groundwaters at the site. However, localised
treatments for hydrocarbon hotspots, as a betterment provision,
include ex situ soil stabilisation, bio-remediation and complex
soil screening.
The remediation for soils incorporates the complex sorting
and removal of asbestos components. The selection of validated
soils as fill materials is related to the sensitivity of the
proposed redevelopment layout.
Difficulties so far encountered by the remediation primarily
relate to obtaining sufficient quality materials to form the
validated capping material in the sensitive residential areas.
This is being resolved by the use of site-won Bracklesham
Beds that have been stabilised to improve their geotechnical
characteristics.
Campbell Reith's geotechnical partner, Elizabeth Brown, explains:
"The use of the Bracklesham Beds, which predominantly
comprise moisture sensitive silty fine sand, was problematic,
especially where the formation was close to the water table.
"Various options were explored with BAM Nuttall and,
in the end, careful control of workmanship combined with enhanced
drainage measures, enabled the performance criteria for most
of the site to be met. In certain areas, where more onerous
performance requirements were set, it was necessary to adopt
cement stabilisation."
In addition to the repair of the deep water quays, part of
the existing river frontage is being engineered to reconstruct
the shoreline in the form of marine terraces. These have been
designed in co-operation with Crest Nicholson, its engineers
and the Environment Agency to enhance the area.
To allow future development, the work also includes the construction
of part of a new adoptable road network and storm and foul
water drainage systems.
Alterations to the existing services, drainage and highways
have also been required.
The advanced works contract is now well advanced and the
£300M mixed industrial and residential development of
the site is on course.
CampbellReith project partner, David Innes, says: "The
regeneration is set to make a significant and welcome change
to Woolston to provide local employment opportunities in the
marine sector as well as both private and low-cost housing.
Article courtesy of Ground Engineering (February 2009)
Further Info
Peter Bishop - Head of Public Relations & Corporate Communication
BAM Nuttall Limited
St James House, Knoll Road, Camberley,
Surrey GU15 3XW
Tel: 01276 63484
Fax: 01276 66060
peter.bishop@bamnuttall.co.uk
|
