Slope instability and valley formation in Canadian soft clay deposits

Abstract

The purposes of the paper are to examine the deepening of valleys in clay deposits of Eastern Canada and in particular to look at the changes in the groundwater regime and slope stability conditions during valley formation. Field observations and laboratory testing indicate that the rate of valley deepening in Champlain clay deposits is of the order of only a few millimetres a year, owing to the low erodibility of the intact clay. The clay banks are, however, more erodible, owing to alteration and fissuration.The stratigraphy of Eastern Canadian clay deposits can be simplified by considering it to be a stratum of low permeabilityconfined between two boundary layers of relatively high permeability, which are the till layer at the base and a weathered crust or coarse-grained layer at the top. As the valley bottom get closer to the bottom till layer, the groundwater regime, and consequently the stability conditions, are modified. During the process of valley formation, the groundwater regime passes through astage where the conditions are rather detrimental to slope stability as it evolves toward conditions that enhance bank stability. Those changes in stability conditions happen over geological time more rapidly or less, depending on clay erodibility. Key words: soft clay, valley formation, slope stability, groundwater, erosion, erodibility.

The Saint-Jude landslide of 10 May 2010, Quebec, Canada: Investigation and characterization of the landslide and its failure mechanism

“…However, the exact influence of such hydraulic conditions on the failure mechanism is still not clear and should be studied further in relation to spreads. These observations indicate that, most probably, the 2010 landslide seems to be of natural origin and triggered by erosion near the toe of the slope with high artesian pressures under the river and deepening of the river with time with a process similar to that described by Lefebvre (1986).…”

Evaluation of potential meteorological triggers of large landslides in sensitive glaciomarine clay, eastern Canada

“…Others have considered the role of piezometric pressure distributions and the interaction of groundwater between the clay and any overlying permeable sandy layers within or below it (Donovan, 1978), the specifics of groundwater flow and model inputs for stability analyses (Lafleur and Lefebvre, 1980), or groundwater pressures and effective stress in relation to underlying topography (Lefebvre, 1986). Precipitation (or its runoff) was discounted as a trigger for several landslides in eastern Canada (e.g.…”

“…While the mechanism by which heavy rain over both short and long antecedent intervals affects the stability of the soil may be debatable, it is clear from previous studies and from our results that a steady supply of surface waters from precipitation or snowmelt are a necessary precondition for landsliding. Others have suggested that regional factors such as funneling or focusing of groundwater due to bedrock topography (Tavenas et al, 1971) or changes in groundwater regimes due to valley formation (Lefebvre, 1986) may also play a role. There are likely several other lurking or hidden variables involved in the triggering or direct cause of large landslides in sensitive clay; we propose that ground frost conditions and timing of the thaw coincident with some other triggering agent could be one of these in eastern Canada.…”

Landslides on river banks in the western part of Podhale (Central Carpathians, Poland)

“…They are mainly found on the high banks of the Vistula River near Nowe Brzesko, Sandomierz, Pu³awy, at the War saw es carp ment, in Dobrzyñ and OEwiecie (e.g., Banach, 1973Banach, , 1977Banach, , 1988Banach, , 1998Bijak, 2007;Ilcewicz-Stefa niuk and Stefaniuk, 2007;Tyszkowski, 2008Tyszkowski, , 2012aTyszkowski, , 2014. Land slides are es pe cially fre quent on banks of ar ti fi cial dam res er voirs (Spanila, 1996), such as at W³oc³awek (Banach, 1985(Banach, , 1994(Banach, , 2004(Banach, , 2006Banach et al, 2013), Pakooeae (Grobelska, 2006) and Jeziorsko (Banach and Grobelska, 2003;Kaczmarek, 2010), or in Si be ria (Shirokov, 1984;Kuskovskiy and Khabidov, 2002;Kozyrieva, 2001;Nazarov, 2006) and China (e.g., Wang et al, 2004;He et al, 2008) but also on the sea cliffs (Lefebre, 1986;Barret et al, 2011). The land slides orig i nated in those places where wa ter was or is now un der cut ting banks of rivers or lakes or where wa ter soaked the banks (Szabó, 2003;Scesi and Gattioni, 2009).…”

“…It has been noted that the course of land slide pro cesses in river banks de pends on the geo log i cal struc ture of the banks (Clifton et al, 1981). The banks cut in young, poorly con sol i dated sed i ments (morainic, lac us trine, ae olian, al lu vial) are eas ily sus cep ti ble to land slides that re sult in sig nif i cant mod i fi ca tion of the chan nel re lief and lo cally al ter the course of chan nel pro cesses (Lefebre, 1986;Pécsi et al, 1987;Miller and Sias, 1998;Har ris, 2003;Kukemilks and Saks, 2013;Chen et al, 2015). Landslides of this type in duce eco nomic loss by de stroy ing build ings and trans port fa cil i ties.…”