Effect of consolidation on the behaviour of excavations in fine-grained soils

This study deals with the detrimental effects of consolidation on the behaviour of excavations carried out in fine-grained soils. With the aim of reproducing the main aspects of the mechanical behaviour of medium-soft clays, an advanced constitutive model was adopted, which is based on bounding surface plasticity and can take into account the damage to the soil microstructure induced by plastic strains. In a first stage of the work, this constitutive model was implemented into a finite element program, and its response was studied through a series of single-element tests, evidencing the effect of the different soil parameters and initial conditions. In the present paper, the constitutive model was used to simulate the behaviour of an idealised excavation, studying the effect of the progressive dissipation of the excess pore water pressures generated during the excavation stages. It was found that, under certain conditions, the initial degree of structure can be progressively lost during consolidation. This detrimental effect produces significant deformation increments and in some cases can drive the system to collapse

Dissipative behaviour of reinforced-earth retaining structures under severe ground motion

This paper focuses on the seismic performance of geosynthetic-reinforced retaining walls (GRWs) that several evidences have shown to be generally adequate. This can be attributed to the dissipation of energy produced by the internal plastic mechanisms activated during the seismic shaking, and to an overall ductile behaviour related to the large deformation that can be accommodated by the soil-reinforcement system. Using a number of numerical computations, this work compares the behaviour of three idealized structures that were conceived in order to have a similar seismic resistance, that however is activated through different plastic mechanisms. The analyses include numerical pseudo-static computations, carried out iteratively to failure, and time-domain nonlinear dynamic analyses, in which acceleration time-histories were applied to the bottom boundary of the same numerical models used for the pseudo-static analyses. The results of the dynamic analyses were interpreted in the light of the plastic mechanisms obtained with the pseudo-static procedure, confirming that GRWs develop local plastic mechanisms during strong motion resulting in a significant improvement of their seismic performance

The Relationship Between Optimism and Perceived Control of Life Events Moderated by the Belief in a Just World

This item is only available electronically.There has been an immense amount of research suggesting that individuals tend to have a biased outlook on life. Previous research has demonstrated that people exhibit three positive cognitive ‘illusions’: believing in a just world (BJW), optimism for the future, and the illusion of control. These psychological constructs have been investigated in great depth respectively; however, there is very limited research that explores these ‘illusions’ together. This study aims to explore the interaction between optimistic bias and control while moderating the level of BJW. A total of 192 participants completed an online self-report survey including the Belief in a Just World Scale, and rating the probability and controllability of experiencing 42 positive and negative life events. Results of this study reveal no significant interaction between BJW-s, control and optimistic bias for positive events. Additionally, there was a significant interaction between BJW-s, control and optimistic bias for negative events, revealing that people who have high BJW-s and high control have lower optimistic bias that negative events will occur to them. These results play a critical role in enhancing overall wellbeing and reducing unwanted health behaviours, such as smoking, by eliminating the optimistic bias that illness will affect others and not oneself.Thesis (B.PsychSc(Hons)) -- University of Adelaide, School of Psychology, 201

China and Africa: Opportunities, Challenges and Forging a Way Forward

Over the past decade, China has actively sought to strengthen its economic and diplomatic relationships throughout the African continent and, in the process, has drawn much praise and incited equal criticism. China’s recent expansion into Africa marks one of the most significant developments in Africa, drawing international attention not only because of its extent but also because of its exponential growth in the areas of trade, investment, diplomatic ties and aid. China became Africa’s third largest trading partner in 2004, with trade volumes rapidly increasing each year. Total trade between Africa and China reached $55.5 billion in 2006, an increase of nearly 40 percent from the prior year. Based on Beijing’s political will, this number seems poised to grow. President Hu Jintao affirmed his commitment to increasing trade and anticipates that increased economic cooperation between China and Africa would lead trade volumes to double, reaching$100 billion by 2010. China’s direct investment in Africa has shown similar levels of growth, increasing from $280 million in 2005 to$370 million in 2006, according to official statistics.

Studio dell'interazione dinamica terreno-spalla-sovrastruttura per una spalla da ponte

La spalla è la parte di un ponte che maggiormente interagisce con il terreno, inoltre il suo comportamento dinamico è influenzato anche dall'interazione con la sovrastruttura, producendo un reciproco scambio di forze di inerzia durante il sisma. In questa nota si illustra una metodologia per l’analisi della risposta dinamica di spalle da ponte attraverso l’applicazione a un particolare caso di studio, per il quale sono disponibili informazioni sia sui terreni di fondazione, sia sulla struttura in elevazione. Lo studio si avvale di modelli numerici di interazione accoppiati sviluppati con il codice di calcolo OpenSees, descrivendo il comportamento meccanico dei terreni mediante il modello costitutivo a plasticità diffusa di Manzari e Dafalias (2004), calibrato sui dati sperimentali. L’interazione dinamica tra la spalla e la struttura del ponte è stata studiata sia mediante la semplice applicazione di forze statiche equivalenti, sia attraverso lo sviluppo di un metodo di validità generale per l’identificazione di un modello strutturale equivalente. Il presente studio si colloca all'interno di un più ampio progetto di ricerca sulla dinamica delle spalle da ponte: in questa nota si mostrano alcuni risultati intermedi riguardanti la risposta sismica locale del sottosuolo Pantano, evidenziando gli effetti di multi-direzionalità del moto sismico, le azioni sismiche trasmesse in fondazione e alcune peculiarità relative alla propagazione del moto verticale

Soil-structure interaction for the seismic design of the Messina Strait Bridge

This paper illustrates an approach to the study of the seismic soil–structure interaction that was developed at the verification stage of the design of the Messina Strait Bridge in order to validate its seismic behaviour. It consisted of a series of two-dimensional, plane strain numerical analyses on models that included, in addition to the embedded foundation elements, a simplified structural description of the bridge towers: simplified structural models were specifically designed to reproduce the first vibrations modes of the towers, that were deemed to have the most significant influence on the system's dynamic response. Non-linear dynamic analyses were carried out in the time domain, studying the effects of two different natural records, each characterised by three orthogonal components of the soil motion. In the first part of the paper, essential information is provided about the foundations layout, the main properties of the foundation soil resulting from the in situ and laboratory investigation, and the assessment of the liquefaction potential. Then, the numerical models are discussed in some detail, with an emphasis on the modelling of the soil and of the structural elements. For sake of conciseness, details are provided only for one of the two shores. The results obtained with the present approach shed some light on the complex coupling between the soil's and the structure's behaviour, evidencing the significant role that the embedded, massive foundations of the bridge play in the dynamic response of the system. The computed time-histories of the displacements of the foundation elements are used to assess the seismic performance of the bridge