A bounding surface hysteretic water retention model for deformable soils

The paper presents a soil water retention model that takes into account the effects of void ratio and hydraulic hysteresis on the variation of degree of saturation. Based on a modified form of the van Genuchten equation, the model defines two bounding surfaces, namely a main drying surface and a main wetting surface, which delimit the region of admissible soil states in the space of degree of saturation, suction and void ratio. Suction and void ratio are then combined into a single auxiliary variable, termed scaled suction, and the main surfaces are recast as main curves in the plane of degree of saturation and scaled suction. The effects of both suction and void ratio on the drying/wetting behaviour of the soil are simply incorporated by relating degree of saturation to scaled suction. The soil is dried when the scaled suction is increased and is wetted when the scaled suction is decreased. The model assumes that, inside the region of admissible soil states, the derivative of degree of saturation with respect to the scaled suction depends on the distance of the soil state from the main curves. This assumption ensures a smooth transition of the drying and wetting paths towards their respective main curves. Interestingly, the derivative of degree of saturation with respect to scaled suction can be integrated in a closed form and all wetting and drying paths can therefore be described by two explicit equations (one for drying paths and one for wetting paths), where different wetting or drying paths are characterised by different values of the integration constant. The integration of the model in a closed form facilitates its implementation into numerical codes. The model requires seven parameters, whose values can be obtained from a single drying\u2013wetting test. Predictions are validated against two different data sets published in the literature, which shows the capability of the model to capture the behaviour observed during laboratory tests on fine-grained soils

Corruption spreads: understanding interorganizational corruption contagion in municipal governments

PurposeCorruption is a major social problem, and scholars have devoted considerable attention to this phenomenon. However, less attention has been paid to how corruption spreads among organizations and what factors can make its spread more likely. This study aims to fill the gap by modelling corruption as an interorganizational contagion.Design/methodology/approachThe authors used social contagion theory to model corruption as an interorganizational contagion, influenced by the susceptibility of organizations and the strength of contagion sources. The study analysed 736 medium and large Italian municipalities over a five-year period, with 3,146 observations (excluding missing data). The authors conducted a longitudinal analysis using panel logistic regression techniques and performed robustness and endogeneity checks through a dynamic panel data model.FindingsThe authors found that municipalities with a higher percentage of corrupt neighbouring municipalities were more likely to experience corruption. The probability of experiencing corruption was also significantly higher for municipalities with weaker organizational resistance to corruption contagion.Originality/valuePrevious studies have not clearly explained the organizational mechanisms behind the spread of corruption at the interorganizational level. The study suggests that corruption contagion at the municipal level occurs via reduced uncertainty in decision-makers and is influenced by the prevalence of corruption locally. The spread can be driven by conscious or unconscious mechanisms. This study challenges the idea that corruption contagion is immediate and inevitable. Organizational resistance to corruption can affect the risk of contagion, highlighting the importance of anti-corruption controls and ethical systems in preventing it

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Unsaturated soils: research and applications

The CD contains the papers presented at the Second European Conference on Unsaturated Soils, E-UNSAT 2012, held in Napoli, Italy, in June 2012. The event is the second of a series of European conferences, born on initiative of the researchers involved in the EU FP6 MUSE – Mechanics of Unsaturated Soils for Engineering – Research and Training Network, and follows the first successful one, organised in Durham, UK, in 2008. The conference series was then supported by Technical Committee 106 of the International Society of Soil Mechanics and Geotechnical Engineering on Unsaturated Soils, which is very active in promoting new opportunities to bring together researchers and practitioners to share advances in unsaturated soils mechanics and related engineering applications. A collection of more than one hundred papers is included in these volumes, addressing the three thematic areas experimental, including advances in testing techniques and soil behaviour, modelling, covering theoretical and constitutive issues together with numerical and physical modelling, and engineering, focusing on approaches, case histories and geo-environmental themes. The areas of application of the papers embrace most of the geotechnical problems related to unsaturated soils. Increasing interest in geo-environmental problems, including chemical coupling, marks new perspectives in unsaturated soil mechanics. We hope this book will provide a valuable up-to-date reference across the subject for both researchers and practitioners. The published contributions, coming from fourteen European countries and another fourteen countries all around the world, were selected after a careful peer-review process. We would like to acknowledge the work done by the reviewers, for their fundamental contribution in assuring the quality of the published papers. We also gratefully acknowledge our colleagues from the Organising and the Technical Advisory Committees and the Authors for the valuable help they provided towards the outcome of the Conference. Special thanks are due to Dr. Marco Caruso, who took charge of the final layout of the publication. The Conference has been endorsed by the Università di Napoli Federico II, and by the Politecnico di Milano. We thank the Italian Geotechnical Society – AGI –for supporting the initiative in the National and the International community. It is, with a sort of romantic attitude, that we acknowledge valued contributions from all the continents, which reminds us of the role played by Napoli in joining cultures and peoples during its long lasting history of more than twenty-eight centuries

Temperature distribution inside and around a lava tube

We propose a model describing the thermal effects of a lava tube. The tube is a circular cylinder, embedded in a solid medium and filled with a Newtonian liquid flowing under the gravity force. Steady-state conditions are considered. The velocity field in the tube, evaluated by the Navier-Stokes equation, is introduced into the heat equation taking into account the viscous dissipation. The temperature distribution is evaluated both inside the tube and in the surrounding solid medium. Under the assumption that the lava tube is embedded in a solid half-space, the surface heat flow due to the presence of the tube is calculated. It is shown that heat flow measurements at the Earth's surface can give information on the depth, size and temperature of the buried lava tube. © 2002 Elsevier Science B.V. All rights reserved

A sequential method for selecting parameter values in the Barcelona basic model

The popularity of the Barcelona basic model (BBM) has grown steadily since its publication in 1990, due to its ability to capture key aspects of unsaturated soil behaviour. Nevertheless, the BBM is still rarely employed by practitioners, partly because of the absence of simple and objective methods for selecting parameter values from laboratory tests. One difficulty is that, in the BBM, individual aspects of the isotropic virgin behaviour are controlled by multiple parameters, while at the same time a single parameter controls more than one aspect of soil behaviour. This has led to iterative procedures where parameter values are adjusted in turn to match experiments, which requires significant experience and can lead to the selection of widely varying parameter values depending on the user. The proposed method streamlines parameter selection with a view to increasing the appeal of the BBM for practitioners. The method adopts a “sequential” procedure where the five parameters governing isotropic virgin behaviour are matched to degrees of freedom in the BBM, which are then fixed one at a time, in a specific order, without any assumption about other parameters. The simplicity and reduced subjectivity of the method in comparison with iterative procedures is demonstrated by selecting parameter values from laboratory tests

Small Strain Behaviour of a Pyroclastic Soil in Unsaturated Conditions

The paper presents part of the experimental results of a wide research program carried out the University of Naples Federico II (Italy) on a pyroclastic soil retrieved from a shallow deposit located in Cava dei Tirreni, 20 km South-East of Naples (Italy). Resulting from volcanic activity, the soil has a grain size distribution ranging from gravel (pumices) to a non-plastic sandy silt and a vacuolar nature of soil particles. The basic mechanical properties of this pyroclastic soil have been widely studied with conventional laboratory tests and usefully integrated by means of extensive in situ testing. This paper focuses on the small strain behaviour of the mentioned soil in unsaturated conditions. Tests have been carried out by using a suction controlled RCTS cell, investigating the volumetric behaviour through isotropic stress paths while measuring almost continuously mechanical and dissipative properties of soil at small strain. Samples have been reconstituted by dry air pluviation technique and then saturated and freezed at constant volume. The results collected along several isotropic stress-paths including compressions and drying/wetting single stages and cycles are presented and interpreted in terms of evolution of Go and Do with net stress, suction and with the plastic volumetric strains caused by the mean net stress and suction. The observed mechanical response is interpreted highlighting the influence of the peculiar nature of the soil and discussing the extension to the unsaturated state of the predictive criteria typically used to estimate the evolu-tion of Go and Do of saturated plastic soils with mean effective stress