Abstract
Compressing samples between rigid platens, as in triaxial testing, induce non-uniform specimen stress, strain and pore water distributions. Although well recognised historically, the effects of such platen restraints are often disregarded or overlooked when performing or interpreting monotonic and cyclic experiments. This paper presents an updated appraisal of end conditions based on laboratory experiments run on sand, glacial till, intact and puttified chalk as part of offshore piling research projects. Monotonic and cyclic triaxial tests are reported that incorporated local strain and pore pressure sensors and a range of platen configurations. New insights are reported regarding the small-to-large behaviour and undrained cyclic pore water pressure measurement.
Highlights
The importance of end restraint in conventional triaxial element testing was investigated in pioneering studies by Rowe & Barden and Bishop & Green ([1, 2])
The current study focuses on the effects of end conditions on soils’ monotonic and cyclic behaviour in triaxial tests
Vinck and Liu ([14, 15]) reported parallel sets of drained monotonic tests on Dunkirk sand that explored the potential effects of end conditions, by considering: (1) A Semi-Rough (SR) configuration, which consisted of a smooth Perspex cap mounted directly on the specimen top, and a standard rough porous disk placed at the bottom, forming a non-symmetric configuration that is commonly seen in triaxial tests involving one-way drainage; (2) A Full-Rough (FR) configuration, which was implemented by placing porous stones at both the top and bottom specimen ends, leading to symmetric, aggravated, constraints at both ends; (3) An Over-sized fully Lubricated configuration in which lubricated disks were placed at both the specimen’s top and bottom ends
Summary
The importance of end restraint in conventional triaxial element testing was investigated in pioneering studies by Rowe & Barden and Bishop & Green ([1, 2]). Zdravkovic et al and Taborda et al ([5, 6]) demonstrate how the Authors’ laboratory tests contributed to the characterisation of site conditions and the calibration of advanced soil constitutive models employed in fully successful 3-D finite element modelling of field tests on large diameter driven piles under lateral and moment loading. The latter formed part of the PISA JIP which developed new paradigms for offshore windturbine foundation design [7]. Illustrative results highlight the impacts of end conditions on: (1) Linear stiffnesses and non-linear and degradation characteristics; (2) Uniformity of pore water pressures within specimens undergoing undrained cyclic loading; (3) Behaviour of structured intact chalk and puttified chalk which exhibit distinctly different and timedependent strength and stiffness features
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