Importance of Lower-Bound Shear Strengths in the Reliability of Spatially Random Clayey Slopes
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ORIGINAL PAPER
Importance of Lower-Bound Shear Strengths in the Reliability of Spatially Random Clayey Slopes Shadi S. Najjar
. Salah Sadek . Zeina Farah
Received: 14 October 2019 / Accepted: 6 July 2020 Ó Springer Nature Switzerland AG 2020
Abstract The random finite element method is used to investigate the effect of including a lower-bound shear strength on the reliability of undrained slopes. The lower bound is represented by the remolded undrained shear strength, which is determined using information about the sensitivity of the clay. This lower-bound strength is used to truncate the left-hand tail of the undrained strength probability distribution. Results indicate that for clayey slopes, the probability of failure is reduced when the lower-bound strength is incorporated in the random field. This reduction allows for reducing the design factor of safety while maintaining the same risk level in the slope design. Keywords RFEM Slopes Probability of failure Clay Reliability
1 Introduction Slope stability analyses are still attracting interest in both academia and practice (Griffiths and Marquez 2007). The stability of a soil slope is traditionally evaluated by adopting a deterministic approach based
S. S. Najjar (&) S. Sadek Z. Farah Department of Civil and Environmental Engineering, American University of Beirut, PO. Box 11-0236, 1107-2020 Riad El-Solh, Beirut, Lebanon e-mail: [email protected]
on a target global factor of safety that is calculated either through limit equilibrium methods or finite element analyses. Due to uncertainties that affect the risk of slope failures, recent studies have attempted to solve slope stability problems using reliability theory. Important steps were taken by several researchers (Li and Lumb 1987; Christian et al. 1994; Malkawi et al. 2000; El-Ramly et al. 2002; Low 2003; Babu and Mukesh 2004; Chow 2007) to investigate the effects of spatial variability in soil properties on the stability of slopes using random field theory and the limit equilibrium method (LEM). A major drawback of the LEM is that it requires a priori assumption of the shape and location of the failure surface. Recently, the random finite element method (RFEM) has been adopted to quantify the effect of spatial variability in soil properties on the risk of failure of slopes (Griffiths and Fenton 2000, 2004, 2008; Griffiths et al. 2007; Fenton et al. 2013; Huang et al. 2013; Griffiths and Yu 2015; Zue et al. 2015, 2017; Yang et al. 2017; Jha and Ching 2013). The random finite element method (RFEM) combines nonlinear finite-element methods with random field generation techniques to quantify the effect of spatial variability in soil properties on the risk of failure of slopes. The RFEM does not predetermine the shape nor the location of the failure plane and is capable of accounting for the soil spatial variability effect by taking into account the spatial correlation structure of the soil and averaging along the failure surface.
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