Abstract
The evolution of the creep strain component in triaxial stress space was investigated through performing a series of multistage drained compression tests on London Clay using a specially designed locally instrumented triaxial apparatus. Experiments along specifically defined stress paths showed significant rotation of the local creep strain component as the samples were sheared towards failure. The results indicate a need for a more complex plastic potential function to correctly predict incremental creep strains at different states in triaxial stress space. Creep deformations for stress path controlled drained compression tests were also found to require a reinterpretation of the classic secondary compression behaviour. Creep strain-rates were found to fall well outside the normal power decay function. Test data and previously reported drained creep test results on London Clay have been combined to provide a complete understanding of the incremental creep component. The experiments show how creep behaviour significantly depends on the stress conditions imposed and the approaching strain rate.
Highlights
The effects of time on the strength and deformation behaviour of soft and stiff clays have been the focus of numerous investigations over the past few decades
Assuming that the time dependent framework proposed by Bjerrum [7] could be applied to the entire limit state surface, Tavenas et al [8] have shown that the volumetric and shear strain components of creep deformations can be described by referring to their position relative to the limit state
Combining the results found for London Clay with those presented by Tavenas et al [8], both of which study the creep behaviour of overconsolidated clays, it can be said that the incremental viscous strain vector rotates towards the direction of the stress path until drained failure where shear strains completely dominate
Summary
The effects of time on the strength and deformation behaviour of soft and stiff clays have been the focus of numerous investigations over the past few decades. The results presented by Leroueil [9] have shown that a general stress-strain-time function may exist which can be expressed in terms of the equation of the limit state surface. Have been formulated to overcome the difficulty of an origin of time by describing the behaviour of a material so that it depends only on its present condition and not as a function of previous history [9] Such models are equivalent to the ’isotache concept’ first suggested by Šuklje [15] as the rate of volumetric deformations are a unique function of the void ratio and the effective stress. Discussion focuses on the viscous behaviour of soil during a multi-stage creep test in order to review the existing understanding of time-dependent phenomena in overconsolidated clays
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