CONTRACT COMPLETION DATE
As part of the new and emerging Millbay Boulevard project, Dorton Group were engaged by Plymouth City Council to remove derelict buildings along part of the development route.
The buildings comprised single storey concrete block workshops, a two storey stone warehouse and their associated hard standings together with a separate area of concrete footprint where office and storage accommodation had been removed several years ago.
The contract specification was for a full enabling works package, to include planning and local authority approvals, service isolations, party wall agreements and asbestos surveys, asbestos removal and demolition to include foundations and floor slab concrete. Completion works required rendering and fencing to the exposed party wall boundary together with additional site hoarding to match existing perimeter protection.
Asbestos surveys revealed asbestos cement roof slates and asbestos cement formwork supporting concrete flat roofs. The slates were removed working from standing scaffold along external site elevations, and from a mobile elevating work platform positioned within site boundaries.
The make-up of the workshop flat roofs comprised a flat asbestos cement sheet spanning the roof beams and profiled asbestos cement sheet above. The roof had then been finished with a 100mm layer of concrete and sealed with a bitumen coating. This type of construction has been used extensively in the Plymouth area and in particular school buildings constructed in the 1960s. Removing the asbestos cement sheets manually was not an option so mechanical demolition methods were used. The roof was removed by machine and pulveriser, in small sections, under controlled water spray suppression. Control measures were monitored by a UKAS accredited analytical company who took both air and personal monitoring samples at key stages during removal of the roof. All samples were found to be within acceptable limits.
With asbestos materials removed demolition of the above ground structures continued using a Zaxis 350 machine. Standing scaffold around the two storey warehouse was dismantled as the building was reduced in height and sections of wall along the party wall boundary with the neighbouring tyre company completed manually. Materials were progressively sorted, with metals being taken to a local metal recycler and general non-recyclable materials taken to a licenced landfill. Surplus aggregate arisings and clean timber were taken to Dorton Groups Challonsleigh Recycling Yard for processing and reuse in the construction, agriculture and allied industries.
Floor slabs and hard standing concrete was then broken out and foundations excavated. The bulk of this material was then crushed to 6F2 specification using Dortons McCloskey J45 crusher. Once the site had been proof dug to remove any residual obstructions the crush material was laid and consolidated to leave a clean and firm base.
During removal of the concrete slabs left from previous demolition works site personnel located small areas of suspect asbestos debris. Works were immediately stopped pending further investigation. Analysis of the fragments showed AIB present in one area and asbestos cement in several other locations where the material had been used to create formwork for a below ground pipe duct.
Working with the clients independent analysts a process was devised where by sub surface material to a depth of 500mm would be screened using a Remu EE3160 mounted screening bucket. An orange demarcation geotextile membrane was installed and a second 100mm sacrificial buffer layer established above this. Screened material was stockpiled in small heaps back allowing detailed sampling of each stockpile. Where stockpiles did not meet criteria suitable for reuse then this material was loaded to tipper lorry and removed from site to licenced asbestos disposal site. As previously works were subject to water spray suppression and independent monitoring of both air and personal exposure for potential asbestos fibre. All testing showed site operations well within acceptable limits.
Once remediation was completed the area was levelled and compacted before finishing with compacted layers of 6F2 crushed demolition material.
A small petrol storage tank, previously made safe and concrete filled was excavated and removed from site. Analysis of soils surrounding the tank required the removal of approximately 40te of contaminated soil which was sent for treatment at a specialist remediation facility in Exeter.
The open party wall elevation was finished with palisade fencing and the building wall made good with a rendered finish.
Site works were completed without accident or incident. Regular communication with neighbouring businesses and prompt action when concerns were raised allowed the project to be completed efficiently and with support of all parties.