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An Analysis on the Kinematics of the Ripley Landslide
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- Author(s) / Creator(s)
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The Ripley Landslide is one of the smallest among the 12 landslides at the Ashcroft-Thompson River Valley, located approximately 10 km south of Ashcroft, B.C. Since it was first identified in 1951, it has been studied by numerous researchers to understand the kinematics controlling its behaviour. Such studies have become vital due to railway tracks owned by Canadian National Railway (CN) and Canadian Pacific Railway (CP) traversing the valley. Both CP and CN have concluded that the most feasible option to mitigate the risks associated with a slide is to actively monitor the behaviour of the slide using precise technology and instrumentation. The site is currently instrumented with GPS devices to monitor the surface displacement at 3 locations, 10 Vibrating Wire Piezometers (VWPs) to monitor the build up of porewater pressure (PWP), and 2 Shape Accel Arrays (SAAs) to monitor the displacement at the primary shear zone.
Purpose of this study was to process, analyze, interpret, and discuss the raw data obtained from these
instrumentations. Establish correlations where applicable. Also, verify existing correlations from published literature using newer data. Aside the instrumentation, barometric data and river flow rate data was also obtained from Environment Canada web data base. The fluctuation of the river matched the fluctuation of the PWP recorded by the VWPs. In addition, from August to April, when the slide is active, the low river level accommodated the slide at velocities averaging 0.34 mm/day. The velocity decreased to an average 0.15 mm/day from April to August when the slide was inactive and the buttress effect from the river was in effect. Unusual precipitation events can lead in to an increase in the PWP within the sliding mass, thus disturbing the equilibrium between the driving and resisting forces against sliding. Such precipitation event was identified in mid-February 2017 which resulted in the slide velocity to increase from 1.04 mm/day to 1.14 mm/day pushing the estimated Factor of Safety via Limit Equilibrium Method below 1.0. The accelerated movement observed in mid-February was concluded to have happened due to precipitation event combined with the river dynamics.Throughout its life, the Ripley slide will continue to undergo active and inactive periods of movement. Changes in topography and PWP conditions will continue to alter the face of the slide posing an imminent risk to the safe operation of the railways. The current GPS system would provide CP and CN personnel a warning of significant surface deformations based on real-time measurements. An alarm system feature of the SAA would also provide an automated warning and should be implemented if costs are not constrained. Once the warnings are received and proper precautions are taken, data from the instrumentation should be processed and analyzed at earliest convenience to understand the changes in subsurface soil and groundwater conditions. Ultimately, based on the historical data, a significant amount of capital would be needed to continue to field monitoring program until a feasible remediation work can be determined.
NOTE:
The executive summary of the submitted report indicates "In addition, from August to April, when the slide is active, the low river level accommodated the slide at velocities averaging 0.15 mm/day. The velocity increased to an average 0.34 mm/day from April to August when the slide was inactive and the buttress effect from the river was in effect" - this shall be replaced with what's noted on the abstract above. The Ripley slide velocity and the Thompsen River level is inversely related. [MSD, Dec 21, 2020] -
- Date created
- 2017-08-21
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- Subjects / Keywords
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- Type of Item
- Report