LESSONS LEARNED FROM FIBER OPTIC MONITORING OF A LANDSLIDE

The Ripley landslide (200 m long x 300 m wide) located 10 km south of Ashcroft, British Columbia is a slow moving translational landslide (25 to 180 mm/year) that is affecting the on-site integrity and safety of railway track for both of Canada’s major rail companies (CN and CP). In 2005 a lock-block retaining wall was installed to reduce the impact of this landslide on the local infrastructure. Two inclinometers and five vibrating wire piezometers installed as part of this mitigation work stopped functioning within a year and a half due to the slide movement. Subsequently survey pins and 4 GPS monitoring stations were installed across the site. Recently a consortium of professionals representing industry, university and government has partnered their efforts to better understand the nature and dynamics of this landslide. A suite of additional mapping and monitoring techniques have now been applied to meet this objective. Additional boreholes, subsurface geotechnical sampling, ground based SAR, corner reflectors for InSAR, LiDAR, ShapeAccelArray (SAA) inclinometry and piezometers have now been added to the repertoire of methods to track and understand the feature. Moreover, non-invasive shallow geophysical techniques were deployed to map the subsurface in detail (electrical resistivity tomography, ground penetrating radar, fixed frequency electromagnetics and seismic refraction).

In conjunction with this multi-parameter approach we also collaborated with specialists from the China Geological Survey and installed fiber optic strain monitoring equipment. Brillouin optical time domain reflector (BOTDR) and Fiber Bragg Grating (FBG) technology were fixed to the retaining wall to evaluate the efficacy of this methodology relative to traditional monitoring methods. Fiber optic data are now being collected in the computer hardware that is housed on site within a self-contained metal bungalow. The data can be accessed, downloaded and analyzed remotely via the internet using wireless technology. Lessons learned during the past 18 months include the effects of extreme weather, local animal hazards, power disruptions and general maintenance practices.