An experimental study was carried out to investigate the shear strength of a compacted non-active clay (Speswhite kaolin). A total of 33 statically compacted specimens were prepared, at vertical stresses of 300, 600 and 1200 kPa and water contents ranging from 0·24 to 0·34. This made it possible to explore a broad range of initial compaction-induced conditions and hence to examine whether differences in water retention characteristics and shear strength are due to differences in initial compaction-induced state or are to be attributed to fundamentally different microfabrics. A shearbox was modified to allow the direct measurement of negative pore water pressure using Trento high-suction tensiometers. Tests were carried out at constant water content by monitoring suction changes. In these tests, it was possible to investigate the transition from unsaturated to saturated states. In the first stage of the test, the specimen was compressed at constant water content. The specimen was therefore wetted, in the sense that its degree of saturation increased. Compression data were then used to investigate the influence of void ratio on the main wetting curve. Shear data were used to put forward a critical state framework for unsaturated compacted clay. This is described by three equations linking shear stress, normal total stress, suction, void ratio and water ratio

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

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