Apr 13 2017

Pinner Wood School – Progress Report, April 12, 2017

Update on works at the site of Pinner Wood School

Dear resident,

This is the first of our regular updates on the work that our project team are undertaking at the site of Pinner Wood School. The site is currently closed after the discovery of previously unmapped chalk mine tunnels under the school building, some of which had collapsed roofs. We have begun by focusing on two priority areas:

  • Surveying the courtyard in the centre of the school to help us better understand the state of the ground underneath the main buildings and the extent of any tunnels there
  • Surveying the school playing field to help us understand if the ground is good enough for us to place a temporary pop-up school for Pinner Wood children there. That would be the quickest and nearest temporary solution for September 2017 if it could be achieved.

We have previously determined that many surveying techniques – such as Dynamic Probingand Ground Penetrating Radar – are of limited use to us, as the mine workings we are looking for are so deep – more than 20 metres underground. That’s why we are exclusively using targeted boreholes at the moment, which give us the most information and the most reliable data down to that depth.

So far we have been using two rigs to drill, provided by contractors Forkers. Following a noise complaint we would like to confirm that work on site should not start until 8am. The rigs first surveyed an area to the north of the school, to make sure an area was safe for a crane. The area was mostly clear but did indicate a potential void – as can be seen on the map below.

The area marked green showed no evidence of any voids or soft ground, so it was considered safe to use for the crane. Today the crane lifted a newly arrived “mini-rig” into the school courtyard. By tomorrow another, larger, rig should have arrived to add to the effort as well. The more rigs we have, the quicker we can complete our surveying work.

The three larger rigs are now diverting their work to surveying the school playing fields in a grid pattern. Early indications suggest there may be some soft ground under the fields, but it is not clear at this early stage what that implies. There will be more information in our next update, once we have completed our scans of the field.

Once the rigs have done the majority of their borehole works, we will bring back the laser scanner to take a fuller look underground in certain areas. The laser scanner is extremely expensive, which is why we are waiting until we have as many areas to examine at one time as we can. Until the laser scanner is deployed, it will be very difficult to get a full picture of what is happening underground.

In conclusion – we are making better progress than expected on surveying the site, and we will
be able to show much more of the site in our next bulletin, due on Wednesday 26th April.


    • Green Circle: Borehole with no evidence of voids
    • Pink Circle: Borehole with evidence of void or significant broken ground
    • Blue/Red Dot: Planned future Borehole
    • Red Hash: Tunnels discovered by March laser surveys
    • Grey Area: School buildings

If you have any other questions, please contact us at regeneration@harrow.gov.uk or by post to Regeneration, Harrow Civic Centre, Station Road HA1 2XY.

Thank you for your understanding and your continuing support.

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