Rockslide on the Sea to Sky Highway


BACKGROUND INFORMATION


The Sea to Sky Highway in British Columbia is historically known to be prone to disasters. This narrow highway runs from Vancouver to Whistler village, home of the 2010 Winter Olympics. Over the past century several tragedies have occurred along the highway, giving it its dangerous reputation. See Table 1 for a description of a few historical events that have caused deaths on Highway 99.
The cliffs adjacent to Highway 99 have several zones of weakness. First, there are major spans of ancient slide surfaces. The historically unstable cliffside has failed an average of 405 times a year. These failures cause fractures in the rocks, which makes the cliff even more vulnerable. Lastly, the majority of disasters on this highway are rock and landslides triggered by heavy rains. Much of the cliffside is clay, which is very weak when it gets wet (Polet, 2/23/2010 Lecture). These jarring statistics were a cause of major concern for athletes and spectators of the 2010 Winter Olympics in Whistler.


Notable Disasters on the
Sea to Sky Highway

Date
Number of Deaths
Debris Flow following heavy rain in Lions Bay
Feb. 11, 1983
2
Heavy rainstorm followed by washout at Britannia Beach
Oct. 28, 1921
37
Falling debris demolishes bridge at M Creek
Oct. 28, 1981
9
Bridge covered by debris at Strachan Creek
Dec. 4, 1981
1
Table 1 | Previous Disasters on Highway 99
Source: The Vancouver Sun




RECENT ROCKSLIDE


The most recent major event on this highway occurred on July 29, 2008. A massive rockslide of about 16,000 cubic meters completely covered a portion of the road between Furry Creek Bridge and Horseshoe Bay (Martineau). As shown in Figure 1, huge portions of the cliffside have fallen into pieces, totally blocking all thru traffic. This type of mass movement can be characterized as a rock fall because of the large pieces of rock that broke off at an almost completely vertical angle. The failure was a disaster waiting to happen. .
aerial.jpeg
Figure 1 | Aerial View of Highway 99 Rockslide
Source: The Star

Pre-existing joints on the cliffside were reportedly “unfavorable” and easy to break (Petley). This situation is often the case when a strong layer overlies a weak layer, as shown in Diagram 1. The road was originally expected to be closed for a period of 24 hours, but clearance crews soon realized that the damage was far more extensive than expected. The cleanup closed the road for five days
diagram.png
Diagram 1 | Weak joints
Source: Lecture

Luckily, there were no deaths associated with this massive event. The only vehicle in the vicinity during the slide was a bus with just a driver and one passenger. The passenger stated that he heard a loud, thunder-like sound. The two didn’t even know that a rockslide occurred until later when the driver pulled over. Figure 2 shows the damage that the bus sustained due to falling debris. Neither the passenger nor the driver knew that the windows had shattered due to the loud noise the actual rockslide caused (“Bus Dodges…).
bus.jpg
Figure 2 | Damage to Bus
Source: Clipmarks



CLEANUP AND HAZARD PREVENTION


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Figure 3 | Demolition to Unstable Rocks
Source: CBC News

Clearance crews worked hard to not only clear up the debris, but also to prevent future rockslides in the area. Demolition crews were brought in to blast unstable rocks on the cliffside that were a potential hazard to the cleanup effort. The blast in Figure 3 occurred on Thursday afternoon, the day after the slide.
Workers were allowed to dispose of the debris in the adjacent bay. They also used the bay to access the site by boat. Drivers were forced to take a 7-10 hour detour while the crew cleared up the highway (“Highway Crew…).


FUTURE CONCERNS


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Figure 4 | Additional Lane and Concrete Dividers
Source: Soompi

This recent cliff failure caused much concern as to what would happen if a similar movement should occur during the Winter Olympics. It is not feasible to create an adequate alternative route from Vancouver to Whistler, so if the road was blocked again visitors would have to take the 8 hour detour that travelers of the 2008 slide did. Construction crews have been hard at work to make the road safer not only for the Olympics, but for the hundred of drivers who use the road every day.
In order to make the road safer to drive on, crews are adding additional lanes, concrete dividers, and wider shoulders (as seen in Figure 4). This will hopefully prevent debris from falling into the water, which in turn will keep the head of the slide from continuing downward.

Major steps have also been made to increase the stability of the slope itself. Scientists have developed double corrosion protected rock bolts specifically for this cliff. These bolts are injected with grout on site and will hopefully prevent future rock falls (“Making Tavelling…”).


PRESENT DAY


Luckily, the closing ceremonies of the Olympics are over and no incidents were recorded on the Sea to Sky Highway. The DCP bolts seem to be holding well and no major rock falls have occurred in this area since the 2008 scare.


WORKS CITED



“Bus Dodges Massive Rockslide on B.C. Coastal Highway”. CBC News, 2008.
“Highway Crew Blasts Rock off Cliff above Slide”. CBC News, 2008.
“Making Travelling Safer”. DYWIDAG-Systems International, 2010.
Martineau, Jarrett. “Massive Rock Slide Closes B.C.’s Sea to Sky Highway”. Now Public, 2008.
Petley, David. “Rockslide on Sea to Sky Highway in British Columbia”. Dave’s Landslide Blog, 2008.
Polet, Jascha. “Mass Movements”. Lecture, February 23, 2010.