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.

This paper presents the results of a laboratory testing program involving consolidated undrained triaxial tests and direct shear tests on remoulded peat, remoulded peat fibre, and Shelby specimens of peat obtained from a field site located in the Edson subdivision of the Canadian National railway in Alberta, Canada. These results were analyzed within the frameworks of elastic behaviour of cross-anisotropic materials and shear strength of fibre-reinforced soil. Shelby specimens were found to be inherently cross-anisotropic, whereas the remoulded peat and peat fibre specimens showed a transition from isotropic to cross-anisotropic with increasing vertical strain and effective confining pressure. The horizontal stiffness of Shelby specimens was found to be 2.6 to 2.9 times their vertical stiffness. The shear strength of intact peat is made up of interparticle friction as well as tension in the peat fibres. A novel procedure for estimating the interparticle frictional strength of fibrous peat from CU triaxial test results is proposed. It involves extrapolating the linear strain-hardening portion of the stress–strain curve to obtain the deviatoric stress at zero axial strain and plotting the deviatoric stress values thus obtained against initial mean effective confining pressure to obtain the frictional strength. Using this procedure, a value of 31° was obtained for the interparticle friction, which compares favourably with a value of 31° obtained from direct shear tests. It is recommended that further studies be undertaken to assess if interparticle frictional strength is an appropriate strength parameter for evaluation of the stability of structures founded on fibrous peat.

This paper presents the deformation and pore-water pressure response within peat foundations below three different railway embankments in response to cyclic heavy axle loading. The study sites include two at Canadian National (CN) Railway's Edson and Lac-La-Biche subdivisions in northern Alberta, and one at CN′s Lévis subdivision in southeastern Quebec. The three sites were instrumented to monitor the spatial distribution of strain, pore pressure generation, and stress, and the distribution of horizontal cyclic displacement with depth during the passage of trains. The horizontal cyclic displacement with depth was measured using a ShapeAccelArray (SAA). An analysis was conducted to determine how close the peat is to yielding under heavy axle loads. This analysis was based on the elastic response determined from undrained triaxial testing, a constitutive model developed for peat, and finite element modelling. The field response and the numerical modelling suggest that the embankments at the northern Alberta sites are stable under current loading conditions. The highest potential for yielding at these sites occurs just beneath the embankment and at the interface between the peat and underlying stiffer soil. At the Lévis site the analysis suggests that a recently constructed ditch concentrates shear stress at a location where the principal stress orientation corresponds to a reduced strength of peat and may have increased the potential for yielding.