Engineering tsunamis in the Coastal Lab

DISASTER PREDICTION: Queen’s civil engineering professors Ryan Mulligan and Andy Take are learning to predict how landslides and landslide-generated waves will behave.

On the evening of October 9, 1963, in the idyllic countryside just north of Venice, Italy, a 400-metre chunk of rock sheared off the side of Mount Toc and slammed into the reservoir behind the Vajont Dam. The dam held, but some 50 million cubic metres of water overtopped it, creating a 200-metre-high wall of fluid and compressed air that sped down the Vajont Valley. Whole villages were destroyed and some 2,000 people died.

It’s that kind of loss of life and destruction of infrastructure that Queen’s civil engineering professors Andy Take and Ryan Mulligan hope to mitigate through their research into landslides and the waves they cause. Mulligan, a coastal engineer who studies the behaviour of waves, and Take, a geotechnical engineer and landslide researcher, are combining their knowledge and skills to shed new light on the mechanics of landslidepropagated tsunamis.

“We’re trying to figure out how much an individual landslide contributes to making that first wave,” says Dr. Take. “How big will that wave be for different water depths and different slide volumes?”

“Tsunamis behave very differently depending on the bathymetry they go over or the different shorelines they hit,” says Dr. Mulligan. “A lot of problems are site-specific, so trying to understand those types of problems more generally is really important.” “ ” Rather than seeing how big a wave a short block of material will create, we can now produce model landslides with more realistic geometries.”

“When we’re looking at landslides there are two problems we’re investigating,” says Take. “One is the mechanics of triggering: What conditions do you need to get a landslide starting to move? The other is how far will it go once it’s moving? We have to understand both of those questions to understand risk.”

To that end, Take oversees a 50-metrelong landslide flume at the Coastal Engineering Lab on the West Campus at Queen’s. The apparatus, which looks a bit like a log-slide ride, was built with funding from a Canada Foundation for Innovation grant and is used to simulate landslides, the waves they generate and the damage they can cause. The first

Engineering tsunamis in the Coastal Lab

Graduate students Alanna Carreira and Gemma Bullard configure instrumentation in the 50-metre-long landslide flume at the Coastal Lab at Queen’s.

The first eight-metre segment of the flume is inclined 30 degrees.

eight metres of the flume is inclined at 30 degrees. The remainder of the flume—the reservoir—is level and can be filled to various depths with standing water. A series of cameras, windows and sensors is arranged at the simulated shoreline where the incline meets the reservoir. Water, gravel, pellets or any combination of simulated slide material is piled at the top of the flume and, when released, rushes down the incline. A wave is propagated when the material hits the shoreline that travels back and forth along the length of the reservoir.

It takes time to set up experiments, but when material is released, the simulation is fast, loud and exhilarating. Data on wave characteristics and photos and video of the impact and wave propagation in cross-section are gathered and analyzed. Take says the sheer size of the flume enables researchers to build more realistic landslides than anything previously available.

“We can use a long block of slide material,” he says. “The aspect ratio is much more realistic, so we can generate simulations with the same characteristics as real landslides. It enables us to ask interesting questions and it will lead to better predictive models of landslide risk.”

This work will help engineers place and design structures to minimize damage and, more importantly, loss of life when landslide disasters, like the one that killed so many in Italy all those years ago, strike populated areas.

“We’re always trying to understand how nature works so we can build better and safer structures or understand erosion better,” says Mulligan. “We want to know where to build buildings, where not to build buildings, and how to stabilize slopes so infrastructure and lives are saved.”

Equipment/features list: > Wave flumes > Large wave basin > Three large scale river simulator flumes > Open channel tilting flume > Landslide flume > Sediment transport flume > Water discolouration facility > Rotating fluids table and two large tanks to study lake/ ocean current interactions Principal investigators include: Dr. Ana da Silva Dr. Andy Take Dr. Leon Boegman Dr. Yves Filion Dr. Ryan Mulligan