Mining Subsidence 2010
A crater near the top of the hill was fenced off while
Bristol City Council and the Coal Authority investigated some subsidence.
This was due to old mine workings
collapsing. Excavations were needed to check whether there was a danger of
any further collapse and to make the area safe. The work has now been completed.
January 2010 - first subsidence
At the end of January when we were on the hill to install the new benches we noticed a hole at the bottom of the 'bomb crater' near the top of the hill above Sally's Glade. At first we thought something had been digging but then we realised that there was no spoil. It looked as though the ground had sunk. We contacted Bristol Parks and they quickly put red & white tape around the area to warn people. Since then the hole has become slightly deeper. Heras fencing has now been put around the hole and the entire area of the crater has been fenced off.
Whilst we didn't know for sure what has caused the subsidence, it seemed most likely that it was as a result of old mine workings. If the crater had been formed by a bomb it seems unlikely that further collapse would be happening now. On our Memories page there is a link to the memories of Tom Fry, who played on Troopers Hill as a child before the First World War and later worked for the Geology Department at Bristol University. He says
'At this time – around 1910— Father used to warn me of the dangers of the hill, telling me that it was all undermined.'
Tom goes on to say
'It may truthfully be said that the hill is the best remaining remnant of the Kingswood coal-field. For one may still trace the sites of at least six shallow mines there'.
On our Forum we heard from Dick Best in Fiji who told us
'I roamed around TH before, during and after WW2 but don't recall ever seeing or hearing of any bombs falling at the top areas. I do remember one or two "hollows" and I think they would have been at the sites of old workings. Probably the new subsidence confirms this.'
How the story unfolded on our now closed forum >>
February to May 2010 - Research and Study
Bristol Parks commissioned a report from Bristol Coalmining Archives and sought the advice of a structural engineer. The report states that 'the circular area, essentially flat with a rim of made ground around the centre is typical of abandoned shafts throughout the coalfield'. As described on our History page, there are known to be mines under Troopers Hill. Friends of Troopers Hill have a copy of a plan of the Fireclay mine that was abandoned in 1908. This mine was accessed by a near horizontal tunnel running from near the river. Bristol Coalmining Archives suggest in their report that this tunnel could have been dug originally to drain an earlier mine that would have been dug in the 1700s. Comparing the location of our shaft with the mine plan, it does appear to be above the access tunnel to the fireclay mine.
Bristol Coalmining Archives conclusion was that it was likely to be a mine shaft dug in the 1700s and that, if so, it was likely to have been about 140 feet deep going down to the Buff Vein.
Works on Site - September 2010
Having spoken to drilling companies about the possibility of bore holes Bristol Parks decided that as a first step an excavator will be used to see if there is any evidence near the surface of a mine shaft.
This work was carried out by a contractor working for the Coal Authority. The method statement for the work was agreed by Bristol City Council and took due notice of the area's status as a Nature Reserve. Prior to the work starting a higher fence was erected around the crater.
The work has now been completed. A concrete cap was installed over the shaft to ensure that there is no future risk of collapse. The excavations did not reveal any evidence of an old shaft.
Photos of work in progress by Bryan:
How the work was reported on our forum >>