Canadian Consulting Engineer

Turtle Mountain Monitoring

October 1, 2006
By Canadian Consulting Engineer

AMEC Earth & Environmental

AMEC Earth & Environmental

Located in southwestern Alberta, Turtle Mountain is the site of one of Canada’s most notorious natural disasters, the Frank Slide. The 1903 rockslide buried the town of Frank under 30 million cubic metres of debris, killing 70 people.

A series of large cracks remains around the South Peak of the mountain, prompting speculation that the cracks may widen over time and lead to another rockslide.

The Turtle Mountain Monitoring Project involved the design of a high-tech monitoring and warning system to detect landslide movement at the South Peak of the mountain.

Monitoring at surface and at depth

Various types of monitoring devices that will measure any movement down to the subtlest, micron-sized shift were installed, some in drilled holes, and some at the surface.

One borehole was drilled at the summit, and into this hole AMEC and other project team members installed sophisticated monitoring equipment to detect movements and changes in conditions around the South Peak. The equipment included geophones, vibrating wire piezometers and thermistors. In addition, an optical televiewer was run down the hole by university researchers to record the locations of cracks and cavities in the rock mass.

All previous work of this nature relied on the geological mapping of bedrock exposed at the surface. Now, continuous images of the bedrock exposed in the walls of the drilled borehole are available. This recorded televiewer data provided the first information on the number and size of fractures and voids in the bedrock beneath the surface.

Following the installation of the downhole instrumentation, the project team installed on the mountain surface a series of tiltmeters and custom-designed surface wire extensometers.

Additionally, the project included the installation of a microseismic monitoring system to help detect minute shifts in the peak. This system was complemented with a groundwater outflow monitoring weir, along with a series of crackmeters, survey prisms and differential GPS stations. Another tool used was an interferometric synthetic aperture radar (InSAR), specifically a technique called coherent target monitoring (CTM). This is the first application of this technology on large natural rock-slopes in western North America.

Establishing alarm thresholds

The monitoring data is relayed by wireless transmission to the Frank Slide Interpretive Centre, three kilometres away. This near real-time data is processed as it is received using customized software. The data is then posted to a secure web site where it can be accessed remotely by specialists in Alberta and beyond. The software compares the data to pre-established alarm thresholds and will automatically notify on-call geohazard specialists and emergency management personnel if necessary. These methods are a great advancement on previous monitoring, which relied on periodic manual readings of instruments at the summit of Turtle Mountain. The summit is generally inaccessible during the winter months.

Working with the new data along with information from climatic and surface seismic stations installed at other locations around Turtle Mountain, the project team helped the provincial government develop monitoring criteria and an emergency response plan for stakeholders in the area.

A remote site; no water

The team faced a variety of challenges from start to finish. Nonetheless, the project was completed successfully on schedule and budget.

All drilling equipment and supplies, for example, were transported via heavy-lift helicopter to the summit. The South Peak is at an elevation of 2,200 metres and is approximately 1,000 metres above the nearest road. Personnel accessed the site either via helicopter or on foot year round. Weather conditions ranged from -30C to +30C, often with extreme winds and electrical storms. There is significant snow cover along the summit ridge during the winter.

Because there was no source of water at the summit, approximately 2,200 litres of water had to be flown in to support the borehole drilling. The water was necessary to mix the grout that held the subsurface instruments in place.

While the team was drilling the 62.5-m deep borehole to install the instruments, the bedrock was fractured and collapsing due to voids and fissures. The project team continuously monitored the borehole conditions during drilling and evaluated the risk of attempting to drill deeper.

The project included the management and coordination of 18 distinct work packages involving 11 contractor-subcontractor companies, two universities and several government agencies. Furthermore, the schedule was fast-tracked from three years to 20 months, partly due to a major forest fire in the Crowsnest Pass area in the summer of 2003 that delayed the startup of the field work.

Name of project: Turtle Mountain Monitoring Project

Award-winning firm: AMEC Earth & Environmental – geotechnical consultants (Andrew Bidwell, P.Eng., Stu Anderson, P.Eng., Drum Cavers, P.Eng., Corey Froese, P.Eng.)

Owner: Emergency Management Alberta, Alberta Geological Survey, Alberta Energy and Utilities Board

Subconsultants and other key players: RS Read Consulting (geotechnical and project management), University of Alberta (Mine Collapse Study), University of Calgary (Fold-Fault Research Project), Gennix Corporation (surface microseismic monitoring), Weir Jones Engineering (subsurface microseismic instrumentation and monitoring), Vertical Systems International (field logistics and mountain safety), Durham Geo Slope Indicator (geotechnical instrumentation), Vexcel (satellite-borne ground movement monitoring), Matrix Solutions (groundwater flow monitoring)


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