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This paper investigates the effect of suction and lime treatment on the volumetric and shear behaviour of a partially saturated high plasticity clay (London Clay). A series of triaxial tests were performed on statically compacted London Clay and lime-treated London Clay specimens. These were prepared at the same target void ratio and tested under partially saturated conditions. The tests concerned isotropic compression and two different types of shearing tests (a) shearing at constant suction and (b) shearing at constant water content, using the axis translation technique. Based on the results, the effects of suction and lime-induced bonding are evaluated and quantified within an elastoplastic partially saturated soil framework.

The paper reviews the common techniques of volume change measurement during unsaturated soil testing, focusing in particular on a newly developed system by the authors. The advantages and accuracy of the system compared to other available volume measurement techniques are discussed. This is followed by the application of the system to the volume change measurement of a lime-treated clay soil during suction-controlled triaxial testing, and a discussion on the behaviour of the soil during shearing.

The paper presents a laboratory investigation, which quantified the beneficial effect of lime on the water retention, compressibility and overall volume changes of a high plasticity clay (London Clay). The study comprised oedometer testing (including suction controlled testing), shrinkage tests, and filter paper testing to determine the soil water retention curves of the drying soils. The latter tests showed that the shallow-mixed lime-treated soils are likely to be partially saturated in situ depending on the environmental conditions; thus, unsaturated soil mechanics concepts are applicable for the description of their behaviour. The oedometer results quantified the marked decrease in the swelling and compressibility of the lime-treated soil compared to the untreated clay and the increase in the vertical effective yield stress (due to suction and cementation bonding). The lime enabled the soil to maintain a more open structure with respect to the untreated soil throughout the compression process, and appears to be the main factor influencing the compressibility of the unsaturated lime-treated soil (rather than suction) for the ranges of suction tested.

The present paper deals with the numerical modelling of trench drainage in variably saturated porous media. In particular, the effect of the unsaturated storage coefficient form on the rate of transient seepage into the trench is investigated. Several numerical analyses are performed for two different soil types. The numerical results derived using a pressure head-dependent storage coefficient, are compared to those derived using constant storage coefficients. It is shown that simplifying assumptions using constant storage coefficients may predict too fast drainage rates.

The paper discusses various models which have been proposed to simulate the hysteresis of the water retention curve. Three of these models were implemented into a finite element computer program for flow in variably saturated porous media and were applied to the solution of transient flow through a soil column subject to drying-wetting cycles. The performance of these models was assessed through comparisons with previously published experimental results. A linear hysteresis model was shown to reproduce satisfactorily the experimental results, although it was simple to implement and required minimal experimental data to be formulated. Overall, the results indicate that the fact of including hysteresis in the numerical model improved the predictions with respect to the case when single-valued functions were used.

The knowledge of the soil water retention curve (SWRC) is of particular importance for unsaturated soils. However common techniques to determine SWRC may be much more time-consuming than other soil property testing techniques and may lack flexibility in controlling the stress state of the soil in the field, which is of most relevance for geotechnical engineering applications. The paper presents a transient testing technique for the continuous measurement of SWRC in a triaxial cell during which testing rates are adjusted based on numerical modeling results simulating the testing. This enables the optimization of the experimental process and hence a more efficient determination of the SWRC. The technique is then successfully applied to determine the SWRC of statically compacted silica flour specimens, tested under different confining stresses.