Experimental investigation of evolving anisotropy in unsaturated soils

This paper investigates the ‘initial’ and ‘evolving’ mechanical anisotropy of a compacted unsaturated soil. Awide campaign of triaxial compression and extension tests, involving different stress and suction paths, has been performed on both isotropically and anisotropically compacted samples of unsaturated Speswhite kaolin. The first objective is the definition of the initial yield surface of the compacted soil after suction equalisation and before any plastic loading/wetting path takes place. This is followed by the investigation of the evolution of the yield surface induced by plastic straining along different loading/wetting paths. Experimental results are interpreted by using two alternative stress variables, namely net stresses σij and Bishop’s stress σ� ij ¼ σij þ δijSrs (where δij is Kronecker delta, Sr is the degree of saturation and s is suction). Constant suction cross-sections of the yield surface are represented as distorted ellipses not passing through the origin in the q:p plane of deviator stress plotted against mean net stress, and by distorted ellipses passing through the origin in the q:p* plane of deviator stress plotted against mean Bishop’s stress. The inclination of these distorted elliptical yield curves evolves with plastic straining but remains the same at all suction levels for a given level of plastic deformation. The critical state lines in the planes q:p and q:p*, or in the semi-logarithmic v:lnp and v:lnp* planes (v is the specific volume), are generally independent of initial anisotropy or stress history, suggesting that fabric memory tends to be erased at critical state

Advances in tensiometer-based suction control systems.

Cunningham (2000) and Jotisankasa (2005) pioneered the development of tensiometer-based suction control systems. In these systems, wetting and drying of the soil are achieved by water injection and circulation of air in contact with the specimen while suction is monitored by sample-mounted high suction tensiometers. Unlike the axis translation technique, these systems avoid using elevated air pressures and better reproduce the drying and wetting conditions occurring in the field. Building upon these earlier works, this pa-per describes an automated tensiometer-based suction control system that enables direct measurement of water content changes inside the sample. A diaphragm pump forces air to flow inside a closed loop that runs across the sample while a moisture trap ensures that the relative humidity of the circulating air is kept low. As the circulating air dries the soil, the amount of abstracted water is measured by continuous weighing of the desiccant inside the moisture trap. Wetting of the sample is instead achieved by controlled injection of water through a solenoid valve connected to a pressurized volume gauge. The changes of soil water content are given by the difference between the amounts of water injected by the volume gauge and that retained by the desiccant. The system is used to impose cycles of drying and wetting on compacted clayey specimens and results from preliminary tests are presented

Rainfall-induced differential settlements of foundations on heterogeneous unsaturated soils

This study stochastically investigates the rainfall-induced differential settlement of a centrally loaded, rigid strip foundation on an unsaturated soil with spatially varying values of either preconsolidation stress or porosity. The differential settlement (between the two foundation ends) is calculated at various times during rainfall by way of a coupled, hydro-mechanical, finite-element analysis. The Barcelona basic model describes the mechanical behaviour of the soil, and the van Genuchten relationships describe water retention and permeability. The variability of soil properties is modelled by means of random fields with spatial correlation in the framework of a Monte Carlo simulation. The study demonstrates that the occurrence of rainfall-induced differential settlements can be consistently analysed using concepts of unsaturated soil mechanics and random field theory. Results show that differential settlements can be vastly underpredicted (or even completely missed) if random heterogeneity and partial saturation are not simultaneously considered. The variation of differential settlements and their statistics during the rainfall depend on the magnitude of the applied load and the statistics of soil variability. Moreover, the transient phase of infiltration and a spatial correlation length equal to the width of the foundation pose the highest risk of differential settlement

A coupled hydromechanical bounding surface model predicting the hysteretic behaviour of unsaturated soils

This paper presents a bounding surface model to predict the hydromechanical behaviour of unsaturated soils under isotropic stress states. The model combines the hydraulic law of Gallipoli et al. [8] with the mechanical law of Gallipoli and Bruno [9]. The hydraulic law relates the degree of saturation to the single variable scaled suction, which accounts for the effect of both suction and void ratio on the water retention behaviour of soils. The hydraulic law is made up of two closed-form equations, one for drying paths and one for wetting paths. Similarly, the mechanical law relates the void ratio to the single variable scaled stress, which accounts for the effect of both stress state and degree of saturation on the deformation of soils. The mechanical law is made up of two closed-form equations, one for loading paths and one for unloading paths. The proposed hydromechanical model is expressed in a finite form and has therefore the advantage of not requiring any approximate numerical integration. The model has been validated against four sets of laboratory data showing a good ability to predict the coupled behaviour of unsaturated soils (e.g. collapse-compression upon wetting) by means of a relatively small number of material parameters

The epigenetic regulators CBP and p300 facilitate leukemogenesis and represent therapeutic targets in acute myeloid leukemia.

Growing evidence links abnormal epigenetic control to the development of hematological malignancies. Accordingly, inhibition of epigenetic regulators is emerging as a promising therapeutic strategy. The acetylation status of lysine residues in histone tails is one of a number of epigenetic post-translational modifications that alter DNA-templated processes, such as transcription, to facilitate malignant transformation. Although histone deacetylases are already being clinically targeted, the role of histone lysine acetyltransferases (KAT) in malignancy is less well characterized. We chose to study this question in the context of acute myeloid leukemia (AML), where, using in vitro and in vivo genetic ablation and knockdown experiments in murine models, we demonstrate a role for the epigenetic regulators CBP and p300 in the induction and maintenance of AML. Furthermore, using selective small molecule inhibitors of their lysine acetyltransferase activity, we validate CBP/p300 as therapeutic targets in vitro across a wide range of human AML subtypes. We proceed to show that growth retardation occurs through the induction of transcriptional changes that induce apoptosis and cell-cycle arrest in leukemia cells and finally demonstrate the efficacy of the KAT inhibitors in decreasing clonogenic growth of primary AML patient samples. Taken together, these data suggest that CBP/p300 are promising therapeutic targets across multiple subtypes in AML.Funding in the Huntly laboratory comes from Cancer Research UK, Leukemia Lymphoma Research, the Kay Kendal Leukemia Fund, the Leukemia lymphoma Society of America, the Wellcome Trust, The Medical Research Council and an NIHR Cambridge Biomedical Research Centre grant. Patient samples were processed in the Cambridge Blood and Stem Cell Biobank.This is the author accepted manuscript. The final version is available via NPG at http://dx.doi.org/10.1038/onc.2015.9

Effect of quick firing on the hygro-mechanical behaviour of earth bricks

\ua9 2019 International Committee of the SCMT conferences. All rights reserved.This paper presents the effect of quick firing on the compressive strength and moisture adsorption capacity of earth bricks manufactured according to three different methods, i.e. extrusion, standard Proctorcompaction and hypercompaction to 100 MPa. All bricks were fired inside an electrical furnace by rising the temperature at a quick rate of about 9 \ub0C per minute to 280, 455, 640, 825 and 1000 \ub0C, after which the furnace was turned off and left to cool to the atmosphere with the brick inside it. Results show that quick firing of hypercompacted bricks at moderate temperatures, between 455 and 640 \ub0C, is enough to attain very high levels of compressive strength, between 29 and 34 MPa, and a good moisture adsorption capacity. The strength of hypercompacted bricks further increases to 53 MPa, a value similar to that of high-strength concrete, after quick firing at 825 \ub0C. Hence, the combination of hypercompaction and quick firing improves material performance while enabling a significant reduction of firing temperatures and times compared to current bricks production methods

Modelling the variation of degree of saturation in a deformable unsaturated soil

An improved relationship for the variation of degree of saturation in an unsaturated soil is presented, incorporating the influence of changes of void ratio. When combined with an elasto-plastic stress-strain model, this is able to represent irreversible changes of degree of saturation and changes of degree of saturation caused by shearing. Experimental data from tests on compacted Speswhite kaolin are used to demonstrate the success of the proposed new expression for degree of saturation. The experimental data involve a wide variety of stress paths, including wetting, isotropic loading and unloading under constant suction, constant suction shearing, and constant water content shearing. Improved representation of the variation of degree of saturation has important consequences for numerical modelling of coupled flow-deformation problems, where the expression used for the degree of saturation can influence significantly the suction generated within the soil and hence the predicted stress-strain behaviour

An elasto-plastic model for unsaturated soil incorporating the effects of suction and degree of saturation on mechanical behaviour

The paper presents an elasto-plastic model for unsaturated soils that takes explicitly into account the mechanisms with which suction affects mechanical behaviour as well as their dependence on degree of saturation. The proposed model is formulated in terms of two constitutive variables directly related to these suction mechanisms: the average skeleton stress, which includes the average fluid pressure acting on the soil pores, and an additional scalar constitutive variable, ξ, related to the magnitude of the bonding effect exerted by meniscus water at the inter-particle contacts. The formulation of the model in terms of variables closely related to specific behaviour mechanisms leads to a remarkable unification of experimental results of tests carried out with different suctions. The analysis of experimental isotropic compression data strongly suggests that the quotient between the void ratio, e, of an unsaturated soil and the void ratio es, corresponding to the saturated state at the same average soil skeleton stress, is a unique function of the bonding effect due to water menisci at the inter-particle contacts. The same result is obtained when examining critical states at different suctions. Based on these observations, an elasto-plastic constitutive model is developed using a single yield surface the size of which is controlled by volumetric hardening. In spite of this simplicity, it is shown that the model reproduces correctly many important features of unsaturated soil behaviour. It is especially remarkable that, although only one yield surface is used in the formulation of the model, the irreversible behaviour in wetting–drying cycles is well captured. Because of the behaviour normalisation achieved by the model, the resulting constitutive law is economical in terms of the number of tests required for parameter determination

Wetting of compacted clays under laterally restrained conditions:initial state, overburden pressure and mineralogy

International audienceCompacted clay fills are generally placed at the optimum value of water content and, immediately after placement, they are unsaturated. Wetting might subsequently occur due, for example, to rainfall infiltration, which can cause volumetric deformation of the fill (either swell or collapse) with associated loss of shear strength and structural integrity. If swelling takes place under partially restrained deformation, due for example to the presence of a buried rigid structure or a retaining wall, additional stresses will develop in the soil and these can be detrimental to the stability of walling elements and other building assets. Factors such as dry density, overburden pressure, compaction water content and type of clay are known to influence the development of stresses. This paper investigates these factors by means of an advanced stress path testing programme performed on four different clays with different mineralogy, index properties and geological histories. Specimens of kaolin clay, London Clay, Belfast Clay and Ampthill Clay were prepared at different initial states and subjected to `controlled' wetting, whereby the suction was reduced gradually to zero under laterally restrained conditions (i.e. K0 conditions). The results showed that the magnitude of the increase in horizontal stresses (and therefore the increase of K0) is influenced by the overburden pressure, compaction water content, dry density at the time of compaction and mineralogy