Pile Mat Construction| Asbestos in Soils Management
John F Hunt Regeneration was contracted in March 2022 by Pocket Living to complete a package of remediation and enabling works to prepare the site known as ‘The Heights’ for redevelopment.
The development proposal included the construction of two interconnected buildings comprising of residential flats, with disabled car parking, cycle parking, and landscaping. The scheme was designed to provide affordable ‘pocket’ homes exclusively for first-time buyers to allow those on lower incomes a way to get on the housing ladder. In line with JFHR’s commitment to sustainability, it was a project that contributed to the United Nation’s ‘Sustainable Cities and Communities’ Sustainable Development Goal.
The 0.26-hectare site comprised of a disused hardstanding area, and a ‘live’ car park that was being used to supply the associated residential housing <10m from the southern boundary.
The Site was historically a sand and chalk quarry, which was subsequently infilled in the 1960’s. Although initial site investigations identified hotspots of elevated lead, total petroleum hydrocarbons (TPH’s), and poly aromatic hydrocarbons (PAH’s). The main contaminant of concern was Asbestos containing materials and loose fibres.
Scope of Works
JFHR was contracted to undertake the initial stage of site clearance and excavation ahead of the ‘phase 2’ construction works. This included:
- removal and disposal of Japanese Knotweed invasive weed species and to provide an insurance backed guarantee for the works
- removal and disposal of soils impacted with Asbestos.
- installation of new infrastructure utilities corridors, drainage and access road.
- construction of a suitable working platform (pile mat) for CMC piling rig.
The removal and disposal of Japanese Knotweed was undertaken under supervision from a certified ecologist. A total of 120 tonnes of soil containing the Knotweed rhizome was removed from site to a contained cell in a certified landfill to prevent any future regrowth. Due to the location of the Knotweed being present along the boundary fence, complete eradication wasn’t possible outside of the boundary, and therefore, a vertical root membrane was placed at the boundary fence to prevent regrowth. Periodic herbicide treatment and inspections were undertaken to achieve the 10-year insurance backed guarantee certificate.
Further to this, Asbestos cement fragments were discovered during the excavation to formation, which was subsequently removed in a controlled manner, dampened, and covered with weighted heavy-duty polythene sheeting to mitigate the risk of release of airborne asbestos fibres. Air monitoring in accordance with the HSE’s ‘Asbestos: The Analyst’s Guide’ (HSG248) removed to a suitably licenced facility for treatment.
Elevated heavy metals, cyanide and petroleum hydrocarbons were also noted across the site in isolated areas which were subsequently characterised for off-site removal in accordance with Technical Guidance WM3 (Waste Classification – Guidance on the classification and assessment of waste).
As part of JFHR’s commitment to the environment and sustainability, where possible, all material removed from site are to be diverted from landfill, and more sustainable treatment facilities are prioritised to promote reuse. As a result, only 120 tonnes of material was sent to a specialist landfill, out of a possible 3,400 tonnes. This equates to a 96.5% diversion from landfill. All material was removed under controlled conditions and disposed of to a suitably licensed facility.
The client had specified a 1m thick piling mat for the follow-on contractors piling rig. JFHR reviewed this requirement with our Temporary Works Designers and the client. By utilising multiple layers of reinforcing geo-grid, the new design managed to reduce the pile mat thickness down to 500mm saving on additional off-site disposal and import of pile mat materials, reducing the disposal and replacement aggregate by ~2000tonnes, which equates to a saving of ~ 3.2tCO₂e.
The UN Sustainable Development Goals this project has contributed to:
The use of Stage IV plant to reduce carbon footprint and fuel consumption by up to 90% in comparison to Stage III plant.
Social
Ensuring a good relationship with the local residents was paramount to this project due to the proximity of their location and the nature of the works.
Due to the sensitivity of the Site, there were stringent criteria set for noise, dust and vibration monitoring, and a specific Community Liaison Officer assigned by JFHR.
JFHR regularly worked with the Principal Contractor to update the residents on the latest requirements and assist with compiling letters to the residents on the progress of the works. This method was used to assist with the change over of the car park when the new utilities were installed which resulted in some car parking spaces being closed for a period of time.
As the relationship had been managed throughout the project, residents were comfortable with approaching the Site to discuss any queries or issues they had which resulted in no Local Authority input and minimal complaints.
Environmental
The site was identified under the Non-Road Mobile Machinery Regulations (NRMM) as part of the ‘Opportunity Area’ zone. As a result, the emissions for the plant used on Site were required to comply with the more stringent emissions standards for the control of dust and emissions on construction sites.
All plant were EU Emissions Stage IV, or above which aided the reduction on carbon emissions through less fuel consumption, and better filters which emit up to 90% less particulate matter and gases than Stage 3 or below combustion engines.