Orbis & Reservoir, Staines
Hughes & Salvidge were appointed the role of Principal Contractor for Enabling and Demolition works at the Orbis Buildings, Lovett Road, Staines, TW18 3AR.
Outline Scope of Works;
- Site Set Up.
- Demolition of above ground structures to Orbis site.
- Breakout and removal required section of Reservoir walls and slab.
- Back fill reservoir with approved design material in compaction regime.
- Tree removal/tree protection.
- Grub up slabs and foundations and crush all arisings.
Superstructure Demolition
The soft-strip of the buildings was largely completed ahead of our arrival on site. There were however a number of known key elements remaining, including solar panels, insulation panels to undercroft and stacked computer flooring.
Prior to commencement of the superstructure demolition there was a final walk round of each facility to ensure the soft stripping was complete and no additional hazardous materials had been left in the buildings. A railway line ran immediately to the south of the site, but there were no works that impacted on this boundary, however careful consideration was given to the railway when planning the works.
The demolition was via mechanical means, working towards the railway elevation. The nature of mechanical demolition of a steel frame works in a top-down sequence, maintaining the stability of the structure at all times through unloading the upper elements before tiering the structure back. At no point was any element of the structure undermined or causing a risk of collapse.
There was sufficient distance between the railway and the closest elevation of the steel framed structure, such that the sequencing of the demolition could allow the buildings to be processed into the site from the footprints of the partially demolished buildings. The steel frame structures were inherently stable when demolished in the top down, bay-by-bay sequence as detailed above.
Substructure Demolition
The sequence for substructure removal followed the same order as the superstructure demolition, with substructure removal commencing as soon as it was practical following the building demolition. The site constraints were taken into account when commencing the works to ensure that a working exclusion zone was always available for the plant undertaking structural demolition works.
Once the operative had been briefed and understood the marked locations of any services in the vicinity, they began exposing the slab and foundations, clearing any of the demolition arisings that may be in the area.
Once a significant amount of ground bearing slab had been exposed, machines fitted with impact hammers and buckets began to remove the slab and foundations. A machine fitted with impact hammer started by puncturing the slab and foundations to break them up to moveable sections. A machine fitted with a bucket then lifted and stockpiled sections ready for further processing. Machines fitted with pulverisers processed arisings further to separate concrete from reinforcing bar, and loaded away respective materials.
All excavations were backfilled progressively and compacted in layers after foundation removal. The area was graded to surrounding site contours, and the footprint tracked in by machine, leaving a flat site.
Reservoir Removal
Contained within the central area of the site was a partially demolished reservoir. The reservoir contained a pre-existing level of water that was free moving with the water table. A large portion of the reservoir had been filled with a crushed aggregate. The water was retained within the area and no pumping works were required to remove the water from the reservoir for the works.
The removal of the reservoir structure was undertaken in a series of phases. A large 360 excavator removed the existing crushed infill and then, utilising an underwater impact breaker, broke the structure of the concrete reservoir in that area.
This broken concrete was then removed from the excavation before it was backfilled with 60mm graded stone in accordance with the agreed backfill regime. The backfill was undertaken in layers and compacted again in accordance with the agreed specification.
Concrete Crushing
Site-won hard inert arisings was crushed on site to produce aggregate for re-use. Concrete/hardcore was loaded into the hopper by an Excavator which is hydraulically fed into the Crusher. The crushed material falls onto the conveyor where any reinforcement bar or other ferrous metal is removed by a hydraulic belt magnet fitted above the main conveyor. The crusher then discharges crushed aggregate and metal into two separate stockpiles. Metal was periodically loaded away into metal bins, and aggregate was regularly cleared and stockpiled in the client’s desired locations. Aggregate stockpiles were formed with a suitable angle of repose to ensure they remained stable and to mitigate any “land-sliding” of aggregate. The Crusher is fitted with a dust suppression system, whereby water is sprayed onto the discharge conveyor to minimise dust. Arising stockpiles were dampened down at regular intervals to mitigate dust release. The area was left clean and tidy on completion.
