Landslides in sensitive clays are a common occurrence (Crawford 1968) and can be triggered by earthquakes, as recognized early by Hodgson (1927). Seismic slope stability is most often assessed using a pseudo-static analysis (Terzaghi 1950) or Newmark’s sliding block analysis (Newmark 1965). The pseudo-static method consists of evaluating the static stability of a slope with an additional horizontal force. The method tends to be over-conservative, except for soils susceptible to loss of stiffness under cyclic loading (Kramer 1996). Newmark’s method assimilates the slope to a rigid block, which does not fail when the factor of safety becomes less than unity but rather accumulates displacement. Shortcomings of Newmark’s method are the assumption of perfect plasticity and the lack of accountability taken for excess pore pressure generation.

Empirical and semi-empirical methods to evaluate slope stability under earthquake loading were derived for granular soils (e.g. Wilson and Keefer 1985) or earth fill and municipal waste (Bray and Travasarou 2007). The latter study was developed based on Newmark’s sliding block mechanism combined with equivalent linear visco-linear modal analysis.

In order to develop a reliable method to evaluate the probability of a seismically induced landslide (SIL), nonlinear simulations will be performed. Case studies of previous SIL will be analyzed in order to define the different factors leading to failure. The objective is to create a regression model based on existing cases and NL simulations in order to assess the probability of a slope failure under earthquake loading without requiring complex simulations. The probability of failure will be a function of slope geometry, soil properties, depth of the groundwater table, shaking intensity, and shaking direction.

References:

Bray, J. D., & Travasarou, T. (2007). “Simplified procedure for estimating earthquake-induced deviatoric slope displacements J Geotech Geoenviron Eng, 133(4), 381-392.

Crawford, C. B. (1968). “Quick clays of eastern Canada.” Engineering Geology, 2(4), 239-265

Hodgson, E. A. (1927). “The marine clays of eastern Canada and their relation to earthquake hazards.” Journal of the Royal Astronomical Society of Canada, 21, 257.

Kramer, S.L., (1996). “Geotechnical Earthquake Engineering.” Prentice Hall, Upper Saddle River, NJ

Newmark, N. M. (1965). “Effects of earthquakes on dams and embankments.” Geotech., 15(2), 139–160.

Terzhagi, K., (1950). “Mechanism of landslides.” In: Paige, S. (Ed.), Application of Geology to Engineering Practice (Berkey Volume). Geological Society of America, New York, NY, pp. 83-123.

Wilson, R.C., Keefer, D.K., (1983). “Dynamic analysis of a slope failure from the 6 August 1979 Coyote Lake, California, earthquake.” Bulletin of the Seismological Society of America 73, 863-877.