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Geotechnical issues
This area is for you to discuss and ask questions about geotechnical issues to do with the Hornsby Quarry site.
This online discussion forum has concluded. You can still browse the site but the discussion area will no longer accept new comments or votes.
Relates to website: http://www.hornsby.nsw.gov.au/uploads/documents/PSM1059.TR1MainReport.pdf
Comment 1 23 Jun 2008, 3:28 PM
Presumably when the quarry was a working quarry, all water was removed - and it was never designed to have water in it.
If water is allowed to accumulate in it, or deliberately retained in it for recreational use, consideration has to be given to the possibility of water seeping into the surrounding landfill parts and making the surrounding areas loose and unstable. Is there any chance of the water freezing, for instance, expanding and so loosening the surrounding rocks? And it all subsequently collapsing in.
Comment 1.1 23 Jun 2008, 8:58 PM
At Frank Slide in Canada in the early 1900s after the spring thaw there was a sudden cold snap which froze water in a fault line resulting in a massive land slide that buried the mining town of Frank.
Over 1,000 people were killed. Most bodies were never recovered. There is now a memorial interpretative centre at Frank Slide.
Whilst this is unlikely to happen at Hornsby, what could occur, unless remedied, is the enclosed valley formed on the north boundary from fill placed by Farley & Lewers (circa 1960 and identified by PSM) could burst in a sudden storm lasting for several hours and fill the creek diversion below resulting in that diverted creek dramatically increasing the quarry water catchment.
It is not known if the risk factor of this occuring has been calculated.
Comment 1.1.1 27 Jun 2008, 10:50 AM
The invitation to the meeting at the RSL on Saturday was for Dr Pells to answer questions about his geotechnical study. At the start of the meeting we were then told that "the focus of the meeting was on the impact of safety and risk issues on the Northern Boundary of the Quarry". Most of Dr Pells's presentation was about the probabilities of a catastrophic land slide of the Northern face - other instabilities were glossed over. The cumulative impact of many smaller instabilities over time would have been more relevant.
Comment 2 24 Jun 2008, 10:07 PM
Increasing the urban density around such an unstable site is setting the council up for enormous liability claims. The site needs to be rehabilitated as it is too close to the town center. How do we know if future councils will have the capacity to monitor the water level, the security fence, and the movement of the walls of the quarry.
Comment 3 30 Jun 2008, 11:15 AM
Dr Pell's presentation was excellent, it was a pity that Council had not seen fit to have this presentation earlier. If the other geotechnical expert (who peer reviewed the Pell report) feels strongly that the Pell report is wrong then he must speak out and request Council to have equal time.
Were the ABC present? Were the ABC invited? If not why not? Will we hear more from the ABC or is the matter closed from their point of view?
Comment 4 7 Jul 2008, 10:53 PM
My father operated a bluestone quarry at Berwick, Vic. from the 1930's to 1950's. In the mid to late 1940's one face of the quarry sank. It did not collapse outwards but sank under the pit floor level and caused an upward eruption of earth and rock some distance from the pit face. It happened overnight without any recognized warning and was of such force that the eruption wrecked the bins crushers and other plant thrusting them several metres into the air, above normal ground level. It was necessary to completely rebuild.I witnessed the above as a young boy and have a clear memory of it. Have the geotechnical experts considered the chances of a subsidence and eruption in Hornsby Quarry area?
The Berwick Quarry area has been turned into "Wilson Botanic Park, Princes Hwy, Berwick, Vic." and can be viewed at Google Earth, where it can be seen that a reasonable buffer area has been maintained around the pit