Friday 24 March 2017

London school closed by sinkholes linked to disused mine workings.

A school in northwest London has been forced to close after a series of sinkholes that opened up in its grounds were found to be linked to disused mineworkings running beneath the site. The first hole appeared in a car park at Pinner Wood School in Harrow appeared in the summer of 2015, prompting Harrow Council to commission an investigation into the site by geotechnical consultants Peter Brett Associates. This survey used laser survey borehole equipment to determine the structure of the ground beneath the school and discovered a series of tunnels, believed to be abandoned early nineteenth century mineworkings, running through a chalk layer 20 m below the surface. These tunnels appear to be beginning to collapse, raising concerns about the safety of structures above them, which has caused Harrow Council to close the school indefinitely while attempts are made to remedy the situation. Lessons will be held at other education facilities in the borough for the time being; it is not yet certain when (or if) it will be possible for the school to reopen.

Digital model of the tunnels below Pinner Wood School. Harow Council.

Sinkholes are generally caused by water eroding soft limestone or unconsolidated deposits from beneath, causing a hole that works its way upwards and eventually opening spectacularly at the surface. Where there are unconsolidated deposits at the surface they can infill from the sides, apparently swallowing objects at the surface, including people, without trace.

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