David H. Huntley

Fiber Optic Strain Monitoring and Evaluation of a Slow-Moving Landslide Near Ashcroft, British Columbia, Canada

Landslides in British Columbia are costly geological hazards that have challenged the major rail companies for over 120 years. Presented here are preliminary results and analyses of fiber Bragg grating and Brillouin optical time domain reflectometry monitoring of a deforming trackside lock-block retaining wall on the Ripley Slide in the Thompson River valley south of Ashcroft, British Columbia. Fiber optic strain data are evaluated in the context of results from global positioning system monitoring, field mapping and electrical resistivity tomographic survey across the landslide. This research aims to reduce the economic, environmental, health and public safety risks that landslides pose to the railway network operating in Canada and elsewhere.

Multi-parameter Monitoring of a Slow Moving Landslide: Ripley Slide, British Columbia, Canada

The Thompson River, south of Ashcroft, British Columbia, Canada is a particularly unique area where complex glacial geology, active geomorphic processes and critical infrastructure (both major national rail lines—CPR and CN) intersect with and are affected by a long history of slope instability. Well documented landslides along a +10 km stretch of the valley have been impacting infrastructure as far back as the 19th century. The Ripley landslide is a small slow moving translational failure that is known to have been active since 1951. It poses a hazard to the onsite infrastructure since both the CN and CPR tracks run adjacent to each other along the entire breadth of the landslide. The economic repercussions of severing both railways here would be pronounced. In response to this threat, an extensive suite of monitoring technology is now being applied that includes: traditional applications including permanent monitoring using GPS stations and piezometers; subsurface investigations involving drilling and shallow seismic surveys; the adoption of novel technologies such as linear fibre optic sensing and vertical subsurface ShapeAccelArray (SAA) inclinometry, the installation of corner reflectors for satellite based (RADARSAT-2) interferometry and the deployment of ground-based SAR and LiDAR for ongoing quantitative assessment. Herein we summarize the collective efforts associated with this extensive array of instrumentation and monitoring studies being undertaken to better manage this and other landslide hazards in Canada and elsewhere.

Combining Terrestrial and Waterborne Geophysical Surveys to Investigate the Internal Composition and Structure of a Very Slow-Moving Landslide Near Ashcroft, British Columbia, Canada

A vital section of Canada’s national railway transportation corridor traverses a 7 km-long section of unstable terrain in the Thompson River valley, British Columbia. Landslides in this region have adversely impacted vital national railway infrastructure and operations, the environment, cultural heritage features, communities, public safety and economy since the late 19th Century. To help manage the potential risks associated with railway operations across this active slide zone, field investigations and monitoring of a very slow-moving Ripley Landslide are being undertaken by a consortium of research partners from government, academia and industry. Knowledge of the internal composition and structure of the landslide as interpreted through surficial geology mapping and geophysical surveys provide contextual baseline data for interpreting monitoring results; in addition to understanding mass-wasting processes in the Thompson River transportation corridor. Bathymetry, electrical resistivity tomography, frequency-domain electromagnetic terrain conductivity, ground penetrating radar, seismic refraction, multi-spectral surface wave analyses, and borehole logging of natural gamma, conductivity and magnetic susceptibility all suggest a moderately high relief bedrock sub-surface overlain by a >20 m thick package of clay, silt, till diamicton, gravel containing groundwater. Planar physical sub-surface features revealed in geophysical profiles and logs include tabular bedding and terrain unit contacts. Field observations and geophysical profiles also show curvilinear-rectilinear features interpreted as sub-horizontal translational failure planes in clay-rich beds beneath the rail ballast and lock-block retaining wall at depths between 5 and 15 m below the surface of the main landslide body. The landslide toe extends under the Thompson River where clay-rich sediments are confined to a >20 m deep bedrock basin. The upper clay beds are armoured from erosion by a lag deposit of modern fluvial boulders except along the west river bank where a deep trough has been carved by strong currents. High waterborne conductivity levels indicate discharge of groundwater through the boulder lag. Fluvial incision of the submerged toe slope at the south end of the landslide is observed <50 m west of where critical railway infrastructure is at risk. Integrating data from surficial geology mapping and an array of geophysical techniques provided significantly more information than any one method on its own.

Innovative Landslide Change Detection Monitoring: Application of Space-Borne InSAR Techniques in the Thompson River Valley, British Columbia, Canada

Open image in new window In this paper we present the first results from Coherent Points Analyses and Differential Stacking of RADARSAT-2 InSAR persistent scatterer interferograms covering a portion of the Thompson River valley, south of Ashcroft in British Columbia Canada. Surface displacements amounting to less than 5 cm/year are detected on landslides that are crossed by national railway infrastructure (train tracks and lock-block retaining walls). Our study shows that many landslides in the Thompson River valley have zones of displacement that are more active than others. For the portions of the North Slide, South Slide and Barnard Slide, zones of active displacement landslide can be resolved within the InSAR data acquired between 2013 and 2016. In contrast, both the Ripley Landslide and Red Hill Slide show marked variations in displacement rates related to seasonal changes in river stage and groundwater level, and compound translational-rotational sliding of coherent blocks of sediment. InSAR techniques effectively capture the surface movement detected by GPS stations, ground-based LiDAR, borehole piezometers and fibre optic installations at the Ripley Landslide test site. This successful application of Coherent Points Analysis and Differential Stacking of persistent scatterer interferograms suggests both techniques are suitable for monitoring unstable terrain in other remote settings where infrastructure, natural resources, the environment, local communities and public safety are at risk.