Overseal
We carried out 3 structural surveys of important adjacent grade II listed buildings in the Overseal area.  The surveys were carried out for different Clients.  The properties had suffered from foundation subsidence over a number of years and this, together with the general lack of maintenance of the buildings, had resulted in complete refurbishments becoming necessary.

Our detailed structural reports on the properties identified that the foundation subsidence had been caused by the development of fissures beneath the properties because of past coal mining activity.  These fissures were present in the rock which was at shallow depth beneath the site.  The rock was overlain by a loose granular soil which was gradually being washed down into the fissures.

The location of the fissures in this area was confirmed by trial holes and a series of shallow sub surface radar probes.  The positions of the fissures were consistent with the foundation subsidence which had taken place.  Although there was no recent coal mining activity in the area, the foundation movement was continuing and therefore a solution had to be found.

Various solutions to the problem were considered, including pressure grouting the fissures, underpinning and piling the foundations.

Following field trials for a grouted solution, it was found that this was unlikely to provide a satisfactory long term answer to the problem, because of the permeability of the ground.  Therefore, in order to come up with the most appropriate solution, it was necessary to include various techniques in the final design.

Detailed drawings were then prepared for the foundation strengthening work, which was necessary to stabilise the properties.