Interface shear box tests for assessing axial pipe-soil resistance

The clay-interface shear resistance is an important parameter for the design of offshore pipelines, which slide on the seabed as a result of thermally induced expansion, contraction and lateral buckling. This paper presents a methodology for characterising the clay-interface resistance and quantifying the effect of drainage and consolidation during or in-between shearing episodes. Models for describing the clay-interface resistance during planar shearing are presented and compared to test data for a range of drainage conditions from drained to undrained and including the case of episodic consolidation. The test data are from two series of interface shear box tests carried out on marine clays. The effects of normal stress level (in the low stress range), overconsolidation and interface roughness are also examined.</p

Analytical modelling of the steady flow of a submarine slide and consequent loading on a pipeline

This paper considers a simple one-dimensional model of a submarine slide at a steady state. From equilibrium relations, the distributions of shear stress, velocity and strain rate across the slide thickness are determined analytically for two rate-dependent soil strength models. Previous work has demonstrated that the increase in shear strength with strain rate can be adequately described using a power law or a logarithmic law model. The analytical solutions obtained with these models are compared with the ones available for a viscoplastic fluid of the Bingham or Herschel-Bulkley types. The influence of the rheological parameters, the slope angle and the slide thickness on the flow and deformation characteristics is analysed for each model. The derived analytical solutions can be viewed as representing a particular position within a slide at a given instant in time. They can be used in conjunction with numerical modelling of the entire slide to provide some insights into the flow pattern, and into the parameter sensitivity. These solutions are also applicable to determination of the loading on a pipeline that is oriented across the path of the slide. They are used to illustrate the relative contributions of the soil strength and the inertial drag, as well as the influence of the vertical position of the pipeline within the slide.</p

Chemo-Mechanical Modelling of Soil or Rock Degradation

peer reviewe

Effects of sampling disturbance in geotechnical design

This paper describes an experimental study of the effects of sampling disturbance in an Australian natural soft clay and the consequences of different sample quality on the representativeness of soil parameters used in geotechnical designs. The paper is divided into three sections. Laboratory test results obtained from specimens retrieved using three different tube samplers as well as the Sherbrooke (block) sampler are first described. Then, the sample quality assessment, using available indices proposed for soft soils, is presented. It is shown that sample quality varies with the stress paths and boundary conditions applied in laboratory tests. Finally, mechanical soil properties derived from specimens retrieved using the different samplers are used in the prediction of two classical problems in soil mechanics: the settlement and excess pore pressure response underneath an embankment as well as the settlement and bearing capacity of a shallow footing. These two examples are used here to highlight the consequences of poor sampling in practice

Modélisation des effets chimiques dans les argiles partiellement saturées.

peer reviewe

Mechanical behavior of intact and remoulded calcareous silts

Calcareous siltsare encountered in many offshore areas where oil and gas exploitationsaretak-ing place (e.g., Arabian gulf, southeastof Brazil, south east and north west of Australia). Understanding be-haviorof calcareous silts remainschallenging as undisturbed siltsamples are difficult to obtain, and most studies rely on remouldedsiltsamples. The purpose of this paperis to characterizethe mechanical behaviorof intact and remouldedoffshore calcareous silts from two different water depths. The comparisons are done based on microstructure characterizationusing scanning electron microscopy (SEM) images supported by in-dex tests, one-dimensional compression tests and undrained monotonic triaxial tests. The results have shown that,except for the critical state friction angle, the behaviour of remoulded silts differs from that of intact silts, due to the change in microstructure, which appears to be more compact with less intact open shellparticles

Modeling contamination of clay.

peer reviewe

Modeling contamination of clay.

peer reviewe

Predicted and measured behaviour of an embankment on PVD-improved Ballina clay

This paper presents Class-A and Class-C predictions of the behaviour of an embankment built on soft Ballina clay improved with prefabricated vertical drains. Predictions were carried out using hand calculations and the finite-difference method. The latter approach allowed the variation of soil parameters and stress levels with depth to be considered in the analyses. An alternative systematic procedure for estimating soil parameters based on high-quality laboratory data is described. Class-A predictions highlighted some disagreement with the measured total settlements and pore pressure dissipation rates. For Class-C predictions, the choice of geotechnical parameters used in the analyses was guided by a systematic assessment of the stress states undergone by soil elements underneath the embankment centreline. This led to a better agreement between predicted and measured data, which demonstrates the potential of the proposed procedure for future analyses of embankment behaviour on soft Ballina clay