From saturated to unsaturated conditions and vice versa
Representing transitions between saturated and unsaturated conditions, during drying, wetting and loading paths, is a necessary step for a consistent unification between saturated and unsaturated soil mechanics. Transitions from saturated to unsaturated conditions during drying will occur at a nonzero air-entry value of suction, whereas transitions from unsaturated to saturated conditions during wetting or loading will occur at a lower nonzero air-exclusion value of suction. Air-entry and air-exclusion values of suction for a given soil will differ (representing hysteresis in the retention behaviour) and both are affected by changes in the dry density of the soil or by the occurrence of plastic volumetric strains. The paper demonstrates, through model simulations and comparison with experimental data from the literature (covering drying, wetting and loading tests), that the Glasgow Coupled Model (GCM), a coupled elasto-plastic constitutive model covering both mechanical and retention behaviour, represents transitions between unsaturated and saturated behaviour in a consistent fashion. Key aspects of the GCM are the use of Bishop’s stress tensor for mechanical behaviour, the additional influence of degree of saturation on mechanical yielding, inclusion of hysteresis in the retention behaviour, and the role of plastic volumetric strains (and not total volumetric strains) in the description of the water retention response. The success of the GCM in representing consistently transitions between saturated and unsaturated conditions, together with subsequent mechanical and retention responses, demonstrates the potential of this coupled constitutive model for numerical modelling of boundary value problems involving saturated and unsaturated conditions.
Investigation into water retention behaviour of deformable soils
The paper presents an experimental and modelling approach for the soil-water retention behaviour of two deformable soils. The objective is to investigate the physical mechanisms that govern the soil-water retention properties and to propose a constitutive framework for the soil-water retention curve accounting for the initial state of compaction and deformability of soils. A granular soil and a clayey soil were subjected to drying over a wide range of suctions so that the residual state of saturation could be attained. Different initial densities were tested for each material. The soil-water retention curves (SWRCs) obtained are synthesized and compared in terms of water content, void ratio, and degree of saturation, and are expressed as a function of the total suction. The studies enable assessment of the effect of the past and present soil deformation on the shape of the curves. The void ratio exerts a clear influence on the air-entry value, revealing that the breakthrough of air into the pores of the s...
Professor Penck's Bluff: Geography, Espionage and Hysteria in World War I
Abstract This article considers the image of geography during World War I through a discussion of newspaper controversies about the pre‐war activities of German and British geographers. Early in the war, Sven Hedin and Albrecht Penck, renowned geographers whose achievements had been widely celebrated by the British geographical establishment, were named in the media as enemy spies whose supposedly disinterested scientific inquiries in Britain and the Empire had masked their real intention to pass sensitive information to the German High Command. British geography stood accused of collusion with enemy ‘super spies’. This article examines how Britain's geographical community, represented by the Royal Geographical Society, sought to defend the discipline's patriotic virtue and head off a full‐scale media witch‐hunt. In so doing, the article comments on the media's role in shaping the image of geography and on geography's place in public debates about the sanctity of the national space.