Liquefação de solos à luz da mecânica aplicada

Há uma crescente convicção da vantagem em encarar o fenómeno de liquefação de solos como passível de ser considerado como um comportamento elasto-plástico que é modelável a partir de conceitos baseados em estados críticos, enquanto se reconhece que pode ocorrer num largo espectro de materiais e condições. Estes assuntos são desenvolvidos neste artigo, atendendo a que as ferramentas de estados críticos têm sido estendidas a outros materiais para além das areias. Esta abordagem integra o conhecimento da influência que a micromecânica das partículas e dos seus contactos tem no comportamento dos solos, e tem em consideração os efeitos da quebra progressiva das partículas e as alterações do grau de uniformidade dos solos no decurso do carregamento. Os objetivos do dimensionamento com base em comportamento são apresentados à luz de ensaios em laboratório e de campo que permitem identificar o risco de se espoletar o fenómeno de liquefação, tanto em condições cíclicas, como estáticas. Também será discutida a forma como os resultados desses ensaios podem ser interpretados para se poder prever o fenómeno, à luz de uma abordagem mecânica global.The advantage of looking at soil liquefaction as an elasto-plastic mechanical behaviour that is well modelled by critical state concepts is well accepted, while recognising that it takes places in a wide range of materials and conditions. These issues are outlined in this paper, as the critical state framework has now been extended to other materials apart from sands. This approach integrates the knowledge of the influence of the micromechanics of particles and their contacts on the observed behaviour, and takes into account the effects of continued particle breakage and change in uniformity. The objectives of performance-based design are presented in the light of laboratory and field tests that permit to identify the risk of triggering both cyclic and static liquefaction. It is also discussed how those tests can be performed and their results interpreted to predict these phenomena, under a global mechanical modelling approach

Indexation of dynamic and static geomechanical properties of a cemented aggregate for transportation engineering

This paper presents an extensive experimental program aiming to the mechanical characterisation of an aggregate stabilised with cement. This geomaterial is the product of a quarry of limestone located in north region of Portugal. The aggregate is often used in current subgrading of infrastructures for transportation, namely in railway lines. Complementary, aggregate-cement admixtures are used for transition zones, such as in between deformable embankments on soft grounds lining on rigid structures, such as bridgesfounded on deep foundations, such as piles or similar. The demand for smooth transition between diverse stiffness zones implies an optimization of the composition of the enriched materials that will be used for such purpose, such as aggregate-cement admixtures. The optimization requires a thorough mechanical characterisation including dynamic tests, with recourse to geophysical techniques, cyclic and monotonic triaxial tests and, ideally,indexed to simple uniaxial compression and indirect tensile tests. The results that will be presented herein have allowed a good mechanical characterisation of the referred aggregate, in terms of the estimation of combinations of the cement content and the admixture compaction level, resulting in new correlations for design purposes

Case-study on lime stabilization of soils for tracks: circuito de velocidad de Los Arcos

Soil stabilization with lime has been assumed to be a good technique for constructing transportation infrastructures. In several conditions, it has been proved that the values of the deformation modulus obtained with these mixtures have greatly exceeded the minimum values specified in design criteria, resulting in supporting layers of roads and railway tracks with characteristics well above the ones necessary for such structures. In these situations, it would be more adequate to take into account this increase in stiffness in the design of upper-level layers, or, alternatively, to consider the decrease in the percentage of lime, in order to optimize the costs of the structural system. Usually, this is not possible since common technical specifications are prepared by default, without taking into consideration an adequate quality control of constructed layers. This optimization could turn this stabilization/treatment technique much more appealing and more economically competitive.Therefore, it seems to be adequate, for quality control purposes, to rely on performance based specifications dully supported by in situ tests aimed to evaluate the mechanical properties of compacted layers, in particular of lime-treated materials, hence enabling an optimization of track design. This paper presents the studies that have been done by taking into consideration in situ tests performed on soils stabilized with lime, during the recent construction of a specific race track in Spain: Circuito de Velocidad de Los Arcos, in the Province of Navarra. The numerical analysis of the results of the tests performed by the Portable Falling Weight Deflectometer (PFWD), on compacted layers of available soils, with and without lime mixing allowed to evaluate the deformation modulus of constructed layers

Case-study on lime stabilization of soils for tracks: circuito de velocidad de Los Arcos

Soil stabilization with lime has been assumed to be a good technique for constructing transportation infrastructures. In several conditions, it has been proved that the values of the deformation modulus obtained with these mixtures have greatly exceeded the minimum values specified in design criteria, resulting in supporting layers of roads and railway tracks with characteristics well above the ones necessary for such structures. In these situations, it would be more adequate to take into account this increase in stiffness in the design of upper-level layers, or, alternatively, to consider the decrease in the percentage of lime, in order to optimize the costs of the structural system. Usually, this is not possible since common technical specifications are prepared by default, without taking into consideration an adequate quality control of constructed layers. This optimization could turn this stabilization/treatment technique much more appealing and more economically competitive.Therefore, it seems to be adequate, for quality control purposes, to rely on performance based specifications dully supported by in situ tests aimed to evaluate the mechanical properties of compacted layers, in particular of lime-treated materials, hence enabling an optimization of track design. This paper presents the studies that have been done by taking into consideration in situ tests performed on soils stabilized with lime, during the recent construction of a specific race track in Spain: Circuito de Velocidad de Los Arcos, in the Province of Navarra. The numerical analysis of the results of the tests performed by the Portable Falling Weight Deflectometer (PFWD), on compacted layers of available soils, with and without lime mixing allowed to evaluate the deformation modulus of constructed layers

A METODOLOGIA FMEA (FAILURE MODE AND EFFECTS ANALYSIS) APLICADA À GESTÃO DE RISCOS DE ESCORREGAMENTOS DE SOLO EM PORTO, PORTUGAL: FMEA (Failure Mode and Effects Analysis) methodology applied to the risk management of landslides in Porto, Portugal

The FMEA - Failure Mode and Effects Analysis methodology is cited in international risk management standards and with use already known in dams and industries in general, which, through the analysis of failure modes and their effects, aims to analyze risks before the events harmful to materialize. The main objective of this research is to propose and adapt the methodology for landslide risk management within the scope of the Civil Protection of Porto, Portugal, in order to allow for lesser discrepancies between evaluators and to encourage the discussion of risks as a team. For such, the following steps are proposed: i) definition of the slopes to be evaluated; ii) development of a field sheet for the analysis of hazards and consequences, attributing points to the indices according to their criticality; iii) risk analysis with definition of scenarios, and combination of hazard and consequences results in a matrix and informative table. Eight soil slopes with different degrees of risk were identified, and the results indicate the applicability of the FMEA method, especially when associated with the field record with quantitative indices, which minimizes discrepancies in the analyzes and facilitates the choice of preventive, mitigating or corrective actions.A metodologia FMEA – Failure Mode and Effects Analysis é citada em normas internacionais de gestão de riscos, e com aplicações já conhecidas em barragens e indústrias em geral, que por meio da análise de modos de falha e seus efeitos busca analisar riscos antes que os eventos danosos se concretizem. O objetivo principal desta pesquisa é propor e adaptar essa metodologia para a gestão de riscos de escorregamentos de solo no âmbito da Proteção Civil do Porto, de forma a possibilitar menores discrepâncias entre avaliadores e fomentar a discussão dos riscos em equipe. Para tal, as seguintes etapas são propostas: i) definição dos taludes a serem avaliados; ii) desenvolvimento de uma ficha de campo para análise de perigosidade e consequências atribuindo pontos para os índices de acordo com sua criticidade; iii) análise do risco com definição de cenários, e combinação dos resultados de perigosidade e consequências em uma matriz e planilha. Foram identificados oito taludes de solo com graus de risco diferentes, e os resultados indicam a aplicabilidade do método FMEA, principalmente quando associado à ficha de campo com índices quantitativos, que minimiza as discrepâncias nas análises e facilita a escolha de ações preventivas, mitigatórias ou corretivas

Suggested methodology for rehabilitation of ancient masonry castles and forts on rock

Forts, including in this designation military castles, present high complexity due to their nature. Methodologiesfollowed in the rehabilitation of forts are briefly presented, with the emphasis on characterization of materials and rockmasses and on tests and numerical models developed for ancient forts. Studies concerning forts with Portuguese legacy arepresented. The first case is related with rehabilitation of foundations and walls of the Guimarães Castle, Portugal. Thecauses of the appearance of holes or torn threads in the exposed face of the wall and the tower of the extreme southwest ofthe castle were assessed. The intervention performed was focused on the stabilization of the rock mass and careful sealingof discontinuities in the high strength rock mass and consolidation of the most weathered fractured rock mass. The secondcase is related to forts existing at Muscat, Oman. The protection of the Jalali Fort is studied in detail. During 2007, cycloneGonu caused substantial damage to the seawall adjacent to the fort. The study addresses the redesign of the seawall.Keywords: masonry forts, rehabilitation, rock mechanics, Guimarães Castle, Jalali Fort

DVD-Multimédia sobre técnicas de Reconhecimento de Maciços Terrosos

DVD-Multimédia sobre técnicas de "Reconhecimento de Maciços Terrosos". Trata-se de uma ferramenta didática onde se descrevem processos de amostragem e ensaios in situ, SPT, DP (DPLD-PSH) - Pen. dinâmicos; CPT, CPTU e SCPTu - Pen. estáticos, com ou sem sísmica; CH (Ensaios sísmico entre furos); FVT (Vane Test); PMT e SBPT (Pressiómetros); DMT (Ensaio com o Dilatómetro Plano); PLT (Carga em Placa)...Trata-se de uma ferramenta Multimédia, que contou com a preciosa colaboração de alguns colegas e empresas da especialidade, inclui texto com uma sucinta descrição dos equipamentos e metodologias, algumas referências normativas, ilustrações fotográficas e vídeos (filmes de ensaios em curso com locução descritiva), tendo um menu que permite acesso simples e independente a cada uma das técnicas. É útil para apoio em cursos que incluem uma componente prática de ensaios geotécnicos, formação em geral de técnicos e profissionais de geotecnia

Caracterização geotécnica de um solo residual do granito da região do Porto

Dissertação apresentada pelo Eng. António Joaquim Pereira Viana da Fonseca à Universidade do Porto para obtenção do grau de Mestre em Estruturas de Engenharia Civi