Understanding how free gas modifies the mechanical behaviour of marine plastic sediments remains a challenging issue. Special triaxial tests were carried out on natural sediments recovered from the Gulf of Guinea. Special attention was devoted to the laboratory preparation procedure, involving saturation of natural marine sediment samples with carbonated water and generation of free gas following undrained unloading. Experimental data show that soil destructuration and damage generated by gas expansion and exsolution are at the origin of (a) the increase in the isotropic compressibility and decrease in the preconsolidation pressure, and (b) the decrease in the peak undrained strength and abrupt increase of the pore pressure during undrained shearing. The experimental data also show that flooding of gas bubbles and dissolution of free gas do not imply a complete strength recovery of natural sediments.

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The paper presents a benchmarking study carried out within the ‘Mechanics of Unsaturated Soils for Engineering’ (MUSE) network aimed at comparing different techniques for measurement and control of suction. Techniques tested by the eight ‘Mechanics of Unsaturated Soils for Engineering’ research teams include axis-translation (pressure plate and suction-controlled oedometer), highcapacity\ud tensiometer and osmotic technique. The soil used in the exercise was a mixture of uniform sand, sodium bentonite (active clay) and kaolinite (non-active clay), which were all commercially available. Samples were prepared by one team and distributed to all other teams. They were normally consolidated from slurry under one-dimensional conditions (consolidometer) to a given vertical stress.\ud The water retention characteristics of the initially saturated specimens were investigated along the main drying path. Specimens were de-saturated by applying suction through the liquid phase when using an axis-translation technique or osmotic method and de-saturated by air-drying,\ud when suction was measured using igh-capacity tensiometers. In general, the same technique was tested by at least two teams. The water retention curves obtained using the different techniques are compared and discrepancies are discussed in the paper.Peer ReviewedPostprint (published version

plastic analysis of the interface behaviour between granular media and structure. Computers and Geotechnics, Elsevier, 2002, 29, N°7, pp. 547-572

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Summary. A series of high pressure oedometer compression tests were carried out on samples of Lixhe chalk (Belgium) containing various pore fluids: water, air (dry sample), oil (Soltrol) and oil/water under a controlled suction of 200 kPa. Strain curves with respect to time of tests carried out under a constant load were examined in a purpose of investigating the time dependent behaviour of chalk. A simple empirical exponential law able to account for the combined effects of stress and suction is proposed. Experiments show that it provides satisfactory results to predict a feature of multiphase chalk behaviour that is important in the study of the behaviour of oilfields.

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