PROJECT EXAMPLE: An excavation contract that uncovered more than knotweed!
Eradication of Japanese knotweed from a property uncovered more than was originally expected. The discovery of asbestos in soils, made ground, manholes and underground pipes, made this project more challenging.
SCOPE OF WORK
The Japanese knotweed removal was required to prepare the site for re-development from an old restaurant and grounds into new residential properties. The site possessed a large stand of Japanese knotweed abutting the boundary of the site, plus a smaller stand near to the old site building.
To enable the proposed development the knotweed required full excavation with arising waste removed from site. Vertical root barrier would be installed to the boundary of the site on completion.
The work was delivered in three phases:
Phase 1: Bio-security watching brief to building demolition including excavation of knotweed near the building and temporary stockpiling on site for later waste removal.
Phase 2: After discovering asbestos-in-soils; testing, hand-picking and removal of asbestos containing materials from site as hazardous waste.
Phase 3: Excavation of the main knotweed area, encountering made-ground, and underground services. Removing final wastes from site and installing a root barrier.
PROJECT Findings & Challenges
Several challenges arose during the project that added to the complexity of the remedial works. As a multi-disciplinary contractor, we were able to manage all these issues directly for the client, saving them time and money.
The common factor between all the challenges encountered was a deep made ground layer sitting atop original ground levels. The made ground was contaminated with asbestos and hid the presence of underground services from the original site levels.
ASBESTOS CONTAMINATED GROUND
In working the site our team spotted potential asbestos containing materials (ACM) in the made-ground soils. Works were suspended to allow us to sample and test the suspected ACM, which was found to be a cement bonded Chrysotile type asbestos. The soils test found no loose asbestos fibre presence in the soil.
We stripped the asbestos contaminated site soils in layers, picking and double bagging all visible ACM pieces. The work was carried out by our knotweed excavation team who are also non-licensable asbestos works trained and insured (a multi-contaminate removal team).
The bagged asbestos was removed from site as hazardous waste. This action cleaned the remaining site soils containing the knotweed, so they were removable from site as non-hazardous waste.
UNDERGROUND OBSTACLES
The site possessed circa 2m deep made ground layer. In excavating the made ground we discovered buried services, relating to the original ground level beneath. A large brick build manhole was uncovered and after verification that its was not live, it was dismantled. Foul pipes were also discovered and part retained, as the foul drainage manhole was to re-built and re-connected on completion of our works.
Removing the manhole and working around the foul drainage pipes allowed all the knotweed within the site boundaries to be excavated.
DEEP KNOTWEED RHIZOME
Excavation of the Japanese knotweed showed that rhizome over a large area was present to depths of 3m. This is unusually deep for knotweed rhizome and was attributed to the made ground layer on the site.
Analysis would suggest either the original ground level contained knotweed (which had grown up through the made-ground level), or the imported made ground was contaminated with knotweed (which had easily grown down to reach a great depth).
The client required full removal and excavations were undertaken to fully remove the knotweed to full depth of its rhizome and up to the boundary, where a vertical root barrier was installed.
Project Outcome
The asbestos contamination was successfully removed, and the client instructed us to check and clear the rest of the site for asbestos under a later re-mobilisation.
All the Japanese knotweed was excavated (up to depths of 3m) and removed from site to landfill in accordance with Duty of Care regulations. Installed vertical root barrier to the boundary now acts as a prevention to offsite knotweed rhizome encroaching back into site.
The site was left in a clean and tidy state ready for the next scheduled development work to commence. The new build properties will benefit from Insurance Backed Guarantees for the knotweed works completed, which will demonstrate to future property owners the successful delivery of eradication works.
We provide a range of excavation options to suit the site and your project needs. To find out more or ask the team a question get in touch.