1 August 2008
Hat tip to Scott McDougall, Erik Eberhardt and Andrew Giles, all from Canada, for this one.
Many readers will be familiar with the classic book “Rock Slope Engineering” by Evert Hoek, which still represents the bible for understanding the mechanisms of failure of hard rock slopes. The cover of the original version featured a photograph of a 1965 rock slope failure on the so-called “Sea to Sky” highway in British Columbia, western Canada:
This highway is the subject of some scrutiny at present as it represents the main transportation link between Vancouver and Whistler, which in 2010 will be hosting the Winter Olympics. The road, which has a history of being landslide prone, is currently undergoing a US$780 million upgrade. In Canada the national, and indeed now the international, press are quite exercised by a failure that occurred on this same road on the night of 29th July. Intriguingly, as Erik Eberhardt has pointed out, this rockslope failure occurred directly next to the 1965 failure featured on the cover of Evert Hoek’s book:
This failure, which has a reported volume of about 16,000 cubic metres, has completely blocked the road and the railway. It appears to have occurred on a set of pre-existing and somewhat unfavourable joints:
The scale of the landslide can be judged from this Reuters image taken from a helicopter. Note the workers on the debris – some of the blocks are rather large:
The inevitable media jamboree appears to be focused on two elements:
1. At the time of the landslide there was a bus passing by that was fortunately not buried but was hit by some of the debris. This has given the media the opportunity to run the traditional story line of a narrow escape. This from the Toronto Star (who incidentally have a great image of the slide taken from a helicopter, plus a video):
2. The inevitable concerns regarding access to the Olympic Games should such an event occur at the wrong moment. So, for example, Vancouver 24 Hours have run this:
“Where is the contingency plan? What would they do in the event of a major accident or a landslide as we see here today?” said B.C. NDP Olympics critic Harry Bains. “When we are inviting the world, we need to assure them that they will be able to watch the Games, that they will not be stuck on some highway for hours.”
In the meantime, the clearance crews are working hard to deal with the debris and the obviously unstable portions of the cliff. CBC News has posted this terrific sequence of images of an unstable block being blasted. This is accompanied by an impressively sensible analysis of the situation on the ground.
Update: The Vancouver Sun has printed some rather interesting statistics about the hazards of this highway:
- “Prior to the improvement project the stretch of highway between Vancouver and Whistler averaged 405 rock falls, slides and debris torrents of varying size and severity each year”
- “Since 1906, at least 50 people have been killed in more than 13 debris torrents, 16 floods and two events of unknown cause that have been recorded on 13 of the 23 creeks along the route.”
Notable events have included:
“Oct. 28, 1921: A heavy Lower Mainland rainstorm triggered a washout that killed 37, injured 15 and flattened 50 houses at Britannia Beach.
March, 1964: Six motorists and passengers missed death by seconds when tonnes of granite thundered on to the highway.
Aug. 25, 1976: A rockslide near Lions Bay knocked the engine of a BC Rail freight train off the tracks and buried 30 metres of road under seven metres of rock and mud
Oct. 28, 1981: Sixty years to the day since the Britannia Beach tragedy, nine people were killed as heavy rains brought down debris that knocked out a bridge at M Creek. Unsuspecting motorists drove over the ripped edge of the bridge into the raging creek below.
Dec. 4, 1981: One person was swept away and drowned when a debris torrent buried a concrete bridge at Strachan Creek.
Feb. 11, 1983: Two teenaged brothers were killed when Alberta Creek, flooded with rain, overturned a small trailer in which they slept and buried it under mud and debris at Lions Bay. A highway bridge and three houses were destroyed.”