1. Numerical assessment of the effects of end-restraints and a pre-existing fissure on the interpretation of triaxial tests on stiff clays
- Author
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Lidija Zdravković, Wenjie Cui, Antonio M. G. Pedro, David M. Potts, and Geotechnical Consulting Group LLP
- Subjects
Deformation (mechanics) ,Fissure ,010102 general mathematics ,0211 other engineering and technologies ,Rotational symmetry ,Numerical assessment ,0914 Resources Engineering and Extractive Metallurgy ,02 engineering and technology ,Geotechnical Engineering and Engineering Geology ,Geological & Geomatics Engineering ,01 natural sciences ,0905 Civil Engineering ,Interpretation (model theory) ,0907 Environmental Engineering ,medicine.anatomical_structure ,Shear strength (soil) ,Homogeneous ,Earth and Planetary Sciences (miscellaneous) ,medicine ,Geotechnical engineering ,Boundary value problem ,0101 mathematics ,Geology ,021101 geological & geomatics engineering - Abstract
Conventional laboratory triaxial tests apply axisymmetric boundary conditions to a cylindrical sample which has an axisymmetric geometry. For a homogeneous sample this implies that the deformed shape of the sample should maintain an axisymmetric geometry during the test. Consequently, the sample should deform in a barrelling mode and if slip planes develop they should define a cup and cone-like failure surface. However, in many triaxial tests such behaviour is not observed, especially as failure is approached when a planar slip surface develops. Such a deformation mode is not axisymmetric. One reason for this behaviour is that a fissure pre-exists in the sample. Employing hydro-mechanically coupled three-dimensional finite-element analyses, this paper investigates the influence of a single fissure in a triaxial sample of stiff clay on its behaviour throughout the test, focusing on the fissure position, orientation, strength and stiffness, in conjunction with the sample's end-restraints (rough or smooth). The effects are quantified in terms of the sample's overall stiffness and strength, indicating that the presence of a fissure can affect the very small strain stiffness, and that it has a significant effect on the strength of the sample, demonstrating that the conventional methods used to interpret laboratory tests may give unconservative results. The results also show a significant effect of the conditions at the top and bottom surfaces of the sample, where in particular the lateral restraint and rough ends introduce ‘bending’ in the sample.
- Published
- 2020