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Safety factors for frictional slips and flow failures in unsaturated soil slopes

This contribution discusses safety factors for shallow natural slopes based on plasticity theories for unsaturated soils. Such failure indices have been derived by identifying the loss of uniqueness and/or existence of the deformation/wetting response predicted by simple models for unsaturated sloping ground. For this purpose, principles of unsaturated soil mechanics, hardening plasticity and soil stability have been combined [Buscarnera, 2014]. Simple constitutive relations have been used to derive closed-form solutions of safety factor for a range of failure mechanisms [Buscarnera and di Prisco, 2011], including frictional slips and flow failures. Such results have allowed us to inspect the role of a number of coupled hydro-mechanical properties, such as, apparent cohesion, suction-hardening processes, and water-retention characteristics. It is shown that such effects play a considerable role on the stress ratios associated with failure, affecting the values of safety factor for all the failure mechanisms under consideration. The proposed expressions have been combined with widely used hydrologic models for water infiltration, and their predictive capabilities have been assessed against literature data for flume tests on highly liquefiable soils. The criteria have been finally incorporated into a GIS platform to capture the spatial and temporal patterns of slope failures at regional scale, thus illustrating the possibility to evaluate the susceptibility to rainfall-induced landslides by encompassing frictional slips and wetting-induced flow failure within the frame of the same modeling approach.

References:

1. Buscarnera, G. "Uniqueness and existence in plasticity models for unsaturated soils." Acta Geotechnica (2014). 9:313-327.

2. Buscarnera, G., and di Prisco C. "Stability criteria for unusaturated shallow slopes" Géotechnique Letters (2011). 1:85-90.

Author(s):

Jose Lizarraga    
Northwestern University
United States

Giuseppe Buscarnera    
Northwestern University
United States