Abstract
In recent years, considerable progress have been made in the study of liquefaction and flow failures with the introduction of the notion of steady-state of deformation and “collapse” envelope. These concepts are increasingly used in seismic stability analysis of slopes or embankments. However, as most of these studies were carried out on clean sands in the triaxial apparatus, one may question the general applicability of these results to practical conditions as several factors such as anisotropy, fines content, undrained strength anisotropy, boundary deformation conditions, stress history, etc. may play an important role. In this paper, the behaviour of the same soil, a loose silty sand, is compared for different loading and testing conditions: drained and undrained triaxial compression tests, drained and constant volume monotonic and cyclic direct simple shear (DSS) tests. Results allow to identify similarities and differences, in terms of undrained initial and steady-state shear strength and modes of undrained failure between triaxial and DSS test conditions and show that liquefaction in DSS cyclic tests is an instability triggered by shear failure developing once the friction corresponding to the characteristic envelope, as identified in the monotonic test, has been mobilized.
Highlights
In recent years, considerable progress have been made in the study of liquefaction and flow failures with the introduction of the notion of steady-state of deformation and "collapse" envelope [1,2,3,4]
The general objective of this paper was to study liquefaction and undrained failure mechanisms for the same loose silty sand subjected to a variety of loading and testing conditions
Static triaxial and direct simple shear (DSS) tests and cyclic DSS tests were conducted on this loose silty sand
Summary
Considerable progress have been made in the study of liquefaction and flow failures with the introduction of the notion of steady-state of deformation and "collapse" envelope [1,2,3,4]. Practical procedures for using steady-state strength concepts in stability analysis of slopes or embankments are available to the design engineer [5]. These studies have notably shown that the effective stress conditions during the steady-state of deformation define a unique strength envelope valid for both static and cyclic loading conditions. A second objective is to use triaxial and DSS tests results to study and characterize yielding, failure and cyclic mobility (or initial liquefaction) as an undrained instability mechanism and to relate the observed behaviour with the static effective strength parameters
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