By Shelby O. MitchellOVERVIEW:
AN AVERAGE WINTER IN QUEBEC CITY
Snowfall (1991-2011): 10 feet
Service area: 2,700 lane miles
Number of dump sites: 14
Total storage capacity: 12.7 million cubic yards
Amount collected: 7.2 million cubic yards
Snow and ice control budget: $60 million
Amount related to dump operations: $1.7 million (2.8%)
After 30 years with the Quebec City Public Works Department, Engineer Eric Langlois has literally written the book on snow and ice removal. It's a subject you can't avoid in one of the world's snowiest cities, where all planning centers around a six-month winter.
Langlois wrote the city's snow removal policy, which defines level of service (including anticipated delays), prioritizes routes, and assigns material — salt, sand, or gravel — based on traffic volume. Dump sites are a crucial part of keeping operations running smoothly.
As the population has grown, residential development has decreased the number of locations suitable for the noisy, unsightly task of dumping collected snow. Finding the ideal spot is a delicate balance. The site has to be far enough from residential areas to avoid noise complaints — as most of the dumping, shoveling, and snow-blowing happens at night — but close enough to be cost-effective. “Distance is the most important cost factor in choosing a dump site,” says Langlois. “If it's too remote you'll need more trucks to keep it in constant operation, which means a bigger price tag.”
Thus, most of Quebec City's dump sites are in flat, industrial zones near highways. They're typically surrounded by a dirt bank, and sometimes trees, to mitigate noise and make the bare site more attractive year-round.
Size is another important consideration. “Design for a larger capacity than you actually need, so the snow dump can be used for 20 years or more,” says Langlois. “Try to anticipate factors such as population growth and unusually heavy snowfall.”Optimizing design and delivery
Over the years, his team has optimized its 14 locations for more efficient use of space as well as equipment operator time, developing what Langlois considers the most effective snow dump design: a rectangular site with just the right combination of heavy equipment.
The city has always used bulldozers to pile the snow deposited by trucks. A Caterpillar 950G loader with plow channels snow into place while a Caterpillar 235C excavator equipped with an 8-cubic-yard bucket stacks it higher onto the pile. By adding heavy-duty snowblowers with 5-7,000 tons of blowing capacity per hour, crews can bank the snow up to 72 feet to maximize space — and process up to 125 truckloads every hour.
To prevent avalanches, operators maintain at least a 45-degree angle from the ground to the top of the snow bank. Abutments made from truck-loads of snow stabilize the pile, and new snow is blown over the top.
With the rectangular site design, operations are choreographed from back to front, and from outside in. The site is divided into two discharge zones, both working toward the middle (see diagram below). Trucks unload from one end and the snowblower processes discharged loads from the other.
Up to 250 trucks an hour arrive through one access point (some dumps have two access points and can process up to 500/hour), and are directed by one to four onsite signalmen, depending on dump site volume. Langlois explains their critical role, not only for traffic control, but also to keep the operation on budget. “It's very important to separate semi-trailers from 10- or 12-wheel trucks because they don't maneuver as easily and move more slowly. If the other trucks have to wait, the city pays more for lost time and the whole operation costs more.”