Pinner Wood School site to close at end of school day after underground chalk mine discovery

News release below:

  • Uncharted chalk mines found under primary school buildings
  • New laser surveys show tunnels have partially collapsed
  • Council and governors take joint decision to close school
  • Council finds new school buildings for Summer Term classes

The site of Pinner Wood School is closing at the end of the school day today, Thursday 23 March, after a joint decision by Harrow Council, the governors and the leadership team of Pinner Wood School.

The reason for the closure is that geotechnical surveys have this week reported an unacceptable risk that the ground beneath the school buildings and playgrounds could become unstable and unsafe, due to the condition of very recently discovered chalk mine tunnels below.

Laser imaging of these previously uncharted and unknown tunnels reveal that they stretch beneath the school buildings and that the mine roofs have collapsed in certain places. These partially collapsed tunnels are likely to open up new surface holes under or near the school at some point in the future. This could put staff and children at risk, prompting today’s decision.

Cllr Sachin Shah, Leader of Harrow Council said:

“With the evidence we have discovered in the past few days, we are certain that this is the right decision. We would like to stress that the imminent risk to the school buildings is believed to be small. However, the Council would never ask or permit any school to operate when there is a known risk, however small, to the safety of the site or the staff and children within it.”

Deb Spruce, Head Teacher of Pinner Wood School, said:

“This is a huge and sudden shock to all of us. We absolutely need to leave this site until it is made safe. Our school is blessed with exceptional staff and governors and a wonderful parent group. I’m certain we will all rise to this challenge and show that our Outstanding school is united by much more than just our buildings.”

The surveys were conducted by Peter Brett Associates and partner Clive Edmonds – Britain’s leading geological engineering expert on chalk mines.

Dr Edmonds said:

“It is likely that the mines date from at least the early 1800s. As is common for chalk mines of this age there are no mine abandonment plans and the mine workings are in a state of breakdown, as confirmed by the laser survey, posing a hazard to surface stability. Our experienced team are purpose-designing suitable investigations to continue to map the workings in order to identify the extent of mining below the school and determine possible remedial options”.

Pupils will not return to the site until further notice. Classes will relocate to other educational settings in Harrow in time for pupils’ schooling to resume at the start of the Summer Term.

If you are concerned or have any questions please email regeneration@harrow.gov.uk

Updates are now available on our dedicated Pinner Wood webpage.

Background information about the closure


During the summer holidays of 2015, a hole unexpectedly opened up in the tarmac of the staff car park at Pinner Wood School. The hole was roughly 3 metres wide and 1 metre deep.

The Council and school made the area safe and commissioned specialist geotechnical engineers, structural engineers, environmental engineers, surveyors, geophysicists and health and safety professionals to analyse the causes of the hole. They determined that the hole was situated on top of an old, disused shaft. The material used historically to backfill that shaft, they concluded, had only been loosely compacted and had subsided – creating a hole.

In the light of that discovery, we undertook to continue our investigations to make certain of the condition of the ground under and all around Pinner Wood School.

Over the past 21 months, extensive studies including probing and drilling had given no reason to believe there is any risk to the stability or safety of the school’s buildings or the site.

Our latest surveys, however, deploying the most modern laser-imaging techniques and deployed from targeted boreholes, have in recent days revealed previously unknown and uncharted chalk mines beneath the school estate, located roughly 20 metres below the surface. Some of these mine tunnels stretch directly underneath the school’s main buildings.

Furthermore, our latest surveys indicate that at least two of the tunnels underneath the school have partial roof collapses. There is also evidence that spoil (largely made up of clay and sand) has fallen from above, into the voids below. It is not known when these collapses occurred.

The professional advice provided to us is that these roof collapses are likely to migrate through the ground and open up new surface holes under or near the school at some point in the future. This could put staff and children at risk or even compromise the structure of the school building.

Furthermore, our work, though extensive, is not exhaustive. It now appears likely from the information we have that there may be further as-yet-undiscovered tunnels, collapses and shafts in other parts of the school estate.

As a result of the professional advice provided to us, the joint view of the Council and the school is that closure of the site is prudent, reasonable and proportionate.

More extensive testing of the ground throughout the site is now essential, to assess the site’s condition and safety. Such a survey is an extremely intrusive process involving rigs, drills and probes and is likely to take months, once the site is vacated.

Our hope and expectation is that, following that comprehensive survey, we will be able to stabilise the ground and return the site to a safe condition – probably by pumping a quantity of material underground to fill the mines themselves. The school would then, subject to a full structural assessment, be able to return to its current site and buildings.

It may, however, be the case that it is not economically feasible to restore the ground and that the school may never reopen in its current form on its current site.

All our investigations have been limited to the school site and although the full extent of the workings are yet to be determined, currently we know of no reason to suggest that the tunnels we have discovered to date stretch under neighbouring properties.