Influence of structure on the time-dependent behaviour of a stiff sedimentary clay

Abstract

In this paper results from laboratory tests on London Clay and artificially cemented kaolin are presented and used to develop a preliminary framework for the timedependent behaviour of soils, applicable to stiff clays and other soils. In the same way that the natural structure of clays has been shown to influence their monotonic behaviour, it is shown that it can also alter their response to changes in strain rate. The relative influence of the two main components of post-sedimentation structure-overconsolidation and diagenesis-on the time-dependent behaviour of London Clay was investigated in triaxial compression tests. The study was carried out in two steps, comparing first the behaviours of normally and overconsolidated reconstituted samples of London Clay subjected to stepwise changes in strain rate, and then the behaviours of overconsolidated reconstituted and undisturbed London Clay samples. The test results show that overconsolidation does not seem to affect the response of reconstituted London Clay to strain rate changes, which is consistent with published data on other stiff clays. However, intact and reconstituted overconsolidated samples show different behaviours, highlighting that it is the elements of structure resulting from diagenesis that influence the time-dependent behaviour of London Clay. Effects of cementing on strain rate sensitivity were investigated in triaxial compression of artificially cemented kaolin. The results obtained were different from the results for London Clay, suggesting that the difference in strain rate effects in the intact and reconstituted London Clay cannot be simply associated with cementing. A preliminary framework is proposed, where the timedependent behaviour of soil depends on its particulate or continuum nature.

Influence of smectite content on the deformation behaviour of clay

“…The effects of structure on the soil mechanical behaviour in shearing and compression for natural London clay have been studied in detail at Imperial College, London (Gasparre et al 2007b;Gasparre et al 2007a;Hight et al 2007;Gasparre 2005) and University College, London (Sørensen et al 2007). During the tests a large effect of particular the post-sedimentation structure was found.…”

Modelling of viscous effects in natural clays

“…The values of , m and reference strain rate were taken from the simulation of the work done by Sorensen et al (2007), while the string lengths were fitted to stiffness degradation data obtained by Gasparre (2005), Figure 7. The fit deviates in the very small strain region to take account of the elastic shear modulus, G max , measured using bender elements.…”

“…Recent testing conducted on London Clay has shown that, not only is the small strain behaviour inelastic and non-linear, but it is also susceptible to the effects of creep and other viscous phenomena (Gasparre et al, 2007;Sorensen et al, 2007). Indeed, the need to take account of creep when conducting triaxial stress path tests is well recognised (e.g.…”

“…The paper provides a brief description of the model, as originally developed, before proposing modifications to cater for viscosity. The performance of the modified model is then tested by simulating laboratory test results in the literature (Leroueil et al, 1985;Graham et al, 1983;Sorensen et al, 2007).…”

Rate effect on the shear resistance of sandy clay in direct shear tests

“…The dilation can cause suction at some conditions of drainage and dilation rate. At critical and residual states (no dilation) the strength of soil remains rather unaffected by the rate of shearing under low to medium strain rate (Sorensen, Baudet & Simpson, 2007;Diaz-Rodriguez, Martinez-Vasquez & Santamarina, 2009;Bhat, Bhandary & Yatabe, 2013). The effect of strain rate on effective strength parameters remains unclear.…”