Buildings #100/101 (Former Canteen)
Before any work could start, a CAT scan of the site was carried out by the demolition supervisor who had received the relevant cable detection training. A Gen was attached to the live incoming gas and electric supplies. These were traced back and their location marked out. Service drawings were then checked to see if all the services identified had been found. All services that entered the site were then isolated. This was documented with an isolation certification provided by the client and a copy was kept within the site office.
Hand digging to locate live services was also required on buildings #100/#101 (former canteen). Before digging could commence, a C-Scope cable avoidance tool was used by a trained Lawson Group operative to scan the area and locate the cables. Once located, their route was marked out using line marker. A suitable location was then selected for the dig. Using correctly insulated spades and shovels, the operatives carefully dug a 1-metre square hole down to the depth of the service. Once the service had been exposed photos were taken and the locations marked.
Japanese knotweed was found behind the canteen and 80-tonnes of material were dug out. This contaminated topsoil was laid out up to 300mm thick on 1,200-gauge polythene sheeting. This material was left on poly sheeting for a three-year quarantine period (possibly five years) – depending on evidence of regrowth or only when the inspectors were happy that all the spores and plants had disappeared.
An ecology report on this building took place, and it was concluded that a bat box needed to be installed amongst the trees nearby. As stated in the ecology report, a cherry picker was used to inspect the building for roosting bats before the soft strip and non-notifiable asbestos could be removed. There were also internal aspects to be considered such as checking behind panels for evidence of bats.
A tree surgeon was subcontracted to carefully cut a corridor in amongst the trees for Lawson Group to gain access round the back of the structure; and to enable the laying of new drains and services later in the project.
Three areas were identified in the Plan of Works for asbestos removal, they were:
• Area 1: Asbestos insulating board to either side of tank room 8m².
• Area 2: Asbestos insulating board above windows to G.04, 4m².
• Area 3: Asbestos insulating board above windows to G.15, 4m².
The enclosure was accessed via an airlock that was fixed to the external side of the enclosure. Tower scaffolding, with a working platform of no more than 2.5 metres, was used to access the AIB panels. For area 1, the fixed scaffolding handrail was approximately 3.5 metres high and had ranch boards fitted. Negative Pressure Units (NPUs) were positioned at the opposite end of the enclosure to the airlock. Waste was carefully removed via a baglock and then through a designated waste route to the enclosed skip. The perimeter of the site was fully enclosed with Heras type fencing to segregate areas.
A decontamination unit (DCU) was set up near to the front of the building and was fully operational throughout the AIB panels above windows process. The enclosures, DCU, airlocks and baglocks were positioned as per the agreed site plan. The pre-formed asbestos removal enclosures were smoke tested prior to becoming operational. Lawson Group ensured that personal air monitoring was carried out during and after removal works using a 4-stage air clearance test.
The removal of asbestos was carried out under fully controlled conditions, it included an enclosure and negative air pressure units; all as per the current CAR Regulations 2012. Lawson Group’s highly trained asbestos operatives were site inducted, this included the reading of the plan of works (POW).
Once the asbestos products had been safely removed, then the demolition of the structures could begin. This building was predominantly of red brick and timber construction and was two storeys in height. There was also a pedestrian access bridge constructed from reinforced concrete with metal railings leading to the main structure.
All fencing carried signage warning of the dangers to others entering the demolition zone during structural mechanical demolition. Dust suppression equipment was set up next to the demolition excavator and a water supply from a fire hydrant was used to supply the tank via a licensed standpipe. The dust boss supplied a cloud of water to the building being deconstructed to dampen down any dust. The operative using the equipment stayed in full view of the excavator driver and was positioned well away from the demolition drop zone. The demolition supervisor monitored the use of water to ensure the minimum amount was used, this reduced the environmental impact of excessive use and water runoff.
All entrances to the building were securely fenced off to ensure no entry was made into the building. The stability of the building was continually monitored by the excavator operator and the demolition supervisor.
Using a demolition excavator with hydraulic grab attachment, the roof was removed back to the first supporting column allowing one bay of the roof to be lowered carefully to the ground floor slab. Once the roof had been removed, the excavator then worked its way in by first removing the gable end and then folding in both side walls. The wood, steel and other associated materials were removed and lowered to ground level away from the building. These materials were then processed and loaded into the designated 40-yard waste bins.
Once the roof had been removed, the internal walls and floors were removed and lowered to ground level. This process of deconstruction was repeated until the entire building and its pedestrian access bridge had been deconstructed. A combination of Cat 323 and Cat 336 excavators were used with hydraulic grabs and pulverisers to demolish the structures. Mechanical crushing followed the demolition and was completed to a 6F2 grade.