Effect of Thompson River elevation on velocity and instability of Ripley Slide

Abstract

Fourteen large landslides have occurred within a 10 km stretch of the Thompson River Valley south of Ashcroft, British Columbia. The slides have had movements ranging from rapid (metres per hour) to very slow, and the largest slides have volumes approaching 15.0 × 106 m3. Investigations of these slides have been conducted since the early failures of the slopes were noted in the 1860s, and have continued with the periodic reactivations and slope movements since then. This paper focuses on the Ripley Slide, which is one of the slides within the Thompson River Valley. This slide is a very slow-moving landslide, which has recently been reactivated. This landslide is crossed by a major transportation corridor and has therefore been the subject of ongoing geotechnical investigation and instrumentation. The results of this investigation are interpreted in light of the wealth of accumulated knowledge from more than a century of geotechnical investigation within this valley. The data collected from the landslide show that, like other slow-moving landslides in this valley, the seasonal fluctuations of the Thompson River elevation strongly influence the instability and the rate of slope movement. Continuous global positioning system monitoring of the movement of the landslide combined with measurement of the pore pressures within the sliding mass and elevation of the river have allowed for an empirical correlation between the limit equilibrium method modelled factor of safety and the velocity of the landslide.

Remote Sensing Applications for Landslide Monitoring and Investigation in Western Canada

“…The location of this section of valley is shown in Figure 8. the current location of the Thompson River and deposits of boulders, gravels, and sands at depths below the interface of units 2 and 3 have been reported in borehole logs [42].…”

“…Fourteen landslides have been identified along a 10 km stretch of the Thomson River Valley, south of Ashcroft, British Columbia, Canada [42]. The location of this section of valley is shown in Figure 8.…”

“…The landslides in the 10 km section of the valley range in volume between 1 and 15 million m 3 and their velocities range from 4 to 30 mm/year to over 100 mm/year, although some have had faster displacement episodes of meters per day to meters per hour [42]. The areal extent of these landslides is shown in Figure 8b.…”

“…After some movements, displaced masses become unstable and active wedges form at the main scarps. The weight of these wedges drives the mass towards the river [42].…”

“…One of these landslides, the Ripley Landslide, has been extensively investigated and shows an annual cycle of deformation accelerating in the Fall (September) and decelerating in the Spring (April), as a response to changes in river elevation. This landslide has shown annual deformations over 100 mm/year [42,44].…”