Rock Face Instability, Kirkburton

Following the sudden collapse of a section of a rock face in the back garden of a detached house in the village of Kirkburton, West Yorkshire, SETS were employed by the owner to investigate the reason for the rock fall.

The house which was only recently completed, had been constructed on a piece of relatively level land immediately in front of a 15m high sandstone rock face. When a SETS geotechnical engineer visited the property, it was evident that a rock fall had partly demolished a wooden shed that was present at one corner of the rear garden.

Measurements of the back garden revealed that the back wall of the house had been constructed some 7.0m from the rock face which rose vertically for some 15m. Above this vertical face open fields were present that sloped steeply down toward the top of the rock face. A 2m high dry stone wall was also observed at the top of the rock face and this had been constructed right on the edge of the rock face and was showing signs of collapse itself.

Detailed mapping of the rock face showed that the sandstone contained both sub horizontal and subvertical discontinuities. Many of the vertical discontinuities (joints) were seen to be open with apertures up to 100mm. In several places within the rock face there was clear evidence of imminent further collapse, due to the geometry of the discontinuities.

Vertical drill holes were also observed within the rock face indicating that the face had been created artificially and was not a naturally occurring sandstone outcrop. The indications were that this was a quarried face.

Based on the findings of the visual inspection and the subsequent study of large scale maps for the area, SETS were able to conclude that the site had originally comprised a quarry. The developer was either unaware of this fact or had ignored the potential dangers associated with the construction of houses so close to an unstable rock face. The property owner was left with the choice of trying to stabilise the rock face, or seeking compensation from the developer.

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