Harrow Council Depot, Greater London

OVERVIEW:

Lawson Group won the contract to soft strip, remove licensed asbestos from, and demolish this former council depot site in Harrow.

CHALLENGE

The site was located on Forward Drive, Harrow. This was a heavily populated residential area and close to a food processing factory, and a local waste deposit site. For these reasons, there was a large volume of traffic, including lorries, entering this road. Good communications and environmental considerations would therefore be required.

The site would need splitting into three phases of work, with phase three consisting of single-storey workshop buildings surrounding a three-storey office block. Surrounding the site was an access road that would have to be closed during the start of demolition, alternative access would have to be organised via gates on the opposite side of the road. The site was made up of buildings that were constructed of a concrete frame with a curved cast-in-situ roof. Inside the buildings were large open spaces, used for the servicing of vehicles.

The West Coast Mainline was located to the south and was 114.2 metres from the demolition zone. Network Rail had been notified of the works, however, due to the location of the buildings being far enough away from the track, Network Rail confirmed they did not need to be involved in the works. The scope of works for this site would include: site set up; erection of scaffolding; CCTV of drains that were to remain; cap off drains that were to be removed at the site boundary; soft strip; asbestos removal; mechanical demolition; loading out of demolition arisings; lifting of slab and foundation; demobilisation of site. Consideration would need to be given to adhering to strict government COVID-19 guidelines.

SOLUTION

Although all services had been terminated, a CAT scan of the site was carried out by Lawson Group to ensure nothing remained live before works commenced. All drainage pipes that left the building were sealed off, this ensured no debris could enter the drainage system and cause a blockage. Storm and foul drains, to be removed, were capped off at the site boundary. This was carried out using stoppers or cement bungs, depending on the sizes and condition of the pipes. As Forward Road had a high volume of traffic, all vehicles entering the site were pre-planned. An appointed banksman controlled all traffic entering the site. For safety reasons, the site boundary fencing remained in place for the duration of the works, this was checked throughout the day by the site supervisor. All access gates were locked at all times when not in use.

Lawson Group operatives were tasked with carrying out soft stripping and worked in teams of not less than two operatives at any one time. Loose contents from within the structure, including furniture, appliances, and loose waste. These were removed by hand in a controlled manner. Arisings were managed in accordance with the Site Waste Management Plan. Door frames and skirting boards were removed by using bars and sledgehammers. All nails and fixings were removed from the walls and the structures’ floors were cleared of general waste and debris prior to demolition. Waste was removed from the building via windows and doors that lead directly to each designated drop zone. All soft strip materials were removed each day to ensure a build-up of combustible material did not occur. This was carried out using a grab attachment on the demolition excavator. Soft strip materials were segregated at site level, with separate waste bins for general waste such as: insulation material, plastics, metal, clean and dirty wood.

An excavator, with a re-handling grab attachment, then loaded the soft stripped material into the appropriate 40-yard waste bins and removed from site in accordance with the Site Waste Management Plan.Once the soft striping had been completed, then licensed asbestos removal could begin. This was carried out under a separate Plan of Works.

Works to be carried out within 1 – Boiler Room Z101, 2 – Electrical, Intake, Z102 & 3 – Gas Meter Room Z103 were:

  • Removal of asbestos thermal insulation residue to walls (216 m2) and thermal insulation residue to pipework under MMMF insulation (357 Lin m) throughout the above areas.

All asbestos containing materials were removed whilst following strict HSE rules. The perimeter of the site was fully enclosed with Heras-type fencing. Removal of asbestos was under fully controlled conditions as per current CAR Regulations 2012. Operatives were site inducted to include reading of the Plan of Works.

A Decontamination Unit (DCU) was set up and operational, airtight enclosures were formed. The DCU, airlocks and bag locks were positioned as per an agreed site plan. Preformed asbestos removal enclosures were smoke tested prior to becoming operational.

Personal air monitoring was also conducted during removal works, with a 4-stage air clearance test also following removal works.

The thermal insulation residues to the pipework, under MMMF insulation, were sprayed with surfactant using airless sprayers. This surfactant was diluted to 1:10 with water. Then the pipework was securely sealed and wrapped in 1,000-gauge polythene. Where a section of MMMF insulation needed to be removed, to allow the pipe to be cut, these sections were sprayed with surfactant using airless sprayers and removed with hand tools. Each removed section of MMMF insulation was carefully placed into waste bags. The ends of the remaining MMMF insulation and pipework that were cut, had tape wrapped around them before being cut.

A hand-arm vibration exposure calculator was completed before any cutting was carried out and results recorded. The pipework was cut into manageable lengths, no longer than 1-metre. These were then wrapped in 1,000-gauge polythene and placed in an asbestos waste bag. This was then taped to the pipework and then disposed of as asbestos waste. The area around any cut was also sprayed whilst cutting was taking place. This mist was applied by utilising a manual spray to prevent the release of asbestos fibres.

Cuts were made at natural breaks in the pipe run and flanges/pipe hangers. Any remaining pipe work with thermal insulation residue were cleaned and removed using hand tools, and immediately place in a ‘UN’ approved asbestos waste bag.

The thermal insulation residues to the walls were also removed using hand tools. The walls were sprayed with the same surfactant using airless sprayers. The walls had all the flaky paint removed as far as was reasonably practical. The walls were then washed down, and the enclosure cleaned.

Once all the asbestos had been safely removed, demolition works could commence on the structures. Due consideration was given to the associated environmental aspects and safety risks relating to the neighbouring properties, close proximity of retained live services, public footpaths, and their location to the site.

Appropriate control measures were employed to mitigate the impacts arising from the production of noise, dust, vibration, and waste arisings; and the potential safety risks to neighbouring properties and members of the general public utilising the adjacent footpaths and highways.

The buildings were to be demolished in their entirety, including removal of ground floor slab and foundations to the footprint of the buildings. An appointed scaffolding contractor installed a 1-metre wide by 8-metre high scaffold along the north and west elevations which met BS EN 12811. This was to contain any falling debris during the demolition process. The scaffold was tied to the building using Excalibur ties, each tie was subject to a pull test with the results recorded and stored in the site file. A full height Monarflex sheet was also installed. A 360-demolition excavator, with pulveriser attachment, was positioned at the front of unit ‘A’.

It started by knocking though the brick walls and exposing the concrete pillars. All concrete columns and roof sections were processed by cutting into manageable lengths and loaded into 8-wheel tipper lorries. After building ‘A’ had been demolished, works carried on through the other units towards and including the Fraikin building.

All general waste and wood products were segregated using hydraulic grabs. These were then stockpiled and loaded into the relevant bins. Once all waste had been processed and removed from each building, the slab was cleaned off using a grading bucket.

All brick and block walls were removed down to ground level, an excavator then stockpiled the hardcore. Once all arisings from the building had been removed from the site, the floor slab was wetted and swept clean.

An excavator, with bucket attachment, then proceeded to lift the slab starting at the edge of the site. The slab was broken into pieces of no bigger than 500cm wide. If required, a breaker attachment was used on a second excavator to achieve this. The slab was stockpiled in different areas, ready for offsite disposal. The foundations of the building were then lifted out and stockpiled ready for breaking. The area of ground from where the foundation had been removed was then backfilled and tracked in. This process was repeated until all foundations had been removed. The foundations were also broken using the hammer attachment into pieces of no bigger than 500cm wide.

RESULT

The site was safely cleared on time and to the client’s satisfaction, ready for the next stage of development.

To find out more on how Lawson Group can help with your next demolition or asbestos removal project, call 01793 782000, email enquiries@lawsongroup.co.uk.