Closure of site
On 23 March 2017, a joint decision was taken by to close the Pinner Wood School site with immediate effect. This decision was taken by:
- Harrow Council
- the leadership team of Pinner Wood School
- the governors
The reason for the closure was due to findings in geotechnical surveys. They showed that an unacceptable risk existed. The ground beneath the school buildings and playgrounds could become unsafe. This was due to the recently discovered chalk mine tunnels below them.
The joint view was that immediate closure of the site was prudent, reasonable and proportionate.
School relocation and works
Following the Easter holidays the youngest pupils would move to the Civic Centre. The classes in question comprised Reception, Year 1, and Year 2. Classes 3 to 6 would be taught at Whitefriars School.
From September 2017 all Pinner Wood School's pupils were taught at the Civic Centre. This would last while works were undertaken on the school site.
The mines beneath the school were mapped by Geoterra. They conducted a subsurface laser scan survey of the voids. This helped them produce a complete 3D point cloud model of the mine. The laser scan survey was used to determine the exact extent and volume of the mine workings.
After discovering all the voids, attention turned to the remediation work. This was carried out by Forkers Civil Engineering Ltd. They filled in the underground voids and borehole areas. This process is called “bulk infilling”.
The second phase of remediation involved “compaction grouting”. This involved injecting grout into the soft areas of ground to stiffen them. In total roughly 5000 tonnes of material was pumped into the ground under the site.
Following the completion of the works Pinner Wood School was able to return to its site. It took only nine months after its original closure.
Reports and documentation
In August 2018 we issued the reports from consultants Peter Brett Associates. They reported on the discovery, exploration and infill of the chalk mines under Pinner Wood School. It is a lengthy document of more than 1,000 pages in total. It can be downloaded in two parts:
- Part 1: Interim Interpretive Report on Subsidence Investigation
- Part 2: Interim Interpretive Report on Subsidence Investigation
The final report and supporting documents are also available online below: