27 October 2008

Interesting slide on Highway 97 in Canada

Posted by Dave Petley

Thanks to Andrew Giles for bringing this one to my attention. Highway 97 in British Columbia is currently being upgraded through the Okanagan Valley (Fig. 1). This project is being undertaken by Arthon – their project website describes this as:

“Four lane roadworks and 1,000,000 m3 rock removal over a 7 km section of BC’s main north-south highway corridor. The B.C. Ministry of Transportation awarded Arthon Contractors Inc. a $38.6 MM contract to complete roadway construction by summer 2009″.

Fig. 1: Google Earth image of the location of the problematic slope on Highway 97.

The rock removal appears to be a widening exercise in which a substantial amount of rock has been removed to create a platform. Unfortunately, last Friday the contractors noticed that a crack had appeared in the slope above the works at the location shown on Fig. 2.

Fig. 2: Google Earth perspective view of the area of the unstable slope before the slope cutting had commenced.

The crack in question is not insubstantial. I must note here that I am very impressed with the openness of those involved – the contractor has placed images on their website of the nature of the problem (Fig 3.), even showing comparison views of the crack opening.

Fig. 3: Arthon Ltd image of the crack on the slope (from the Arthon Ltd web page)

The block of rock that is moving is large – about 300,000 cubic metres (Fig. 4), with the crack at the rear extending downwards for at least 10 m.

Fig. 4: Arthon Ltd image of the mobile block (from the Arthon Ltd web page)

Unsurprisingly, the authorities have stopped both the work on the slope and the traffic on the road, and now it is a game of wait and see. One possibility is that the slope will collapse completely, it may keep creeping or it may stop. Whatever happens the authorities have quite a challenge on their hands to know how to deal with this slope. The pattern of displacement against time is one tool that could be used in this case.

I’ll post again as this develops. In the meantime, congratulations to all for their transparency in this case.