| Summary: |
Earthquakes are one of the most destructive natural phenomena. The increasing frequency and severity of seismic activities poses a serious threat to buildings and physical assets located in vulnerable locations, including critical infrastructures (i.e. public buildings, such as government offices, transport stations, terminals, historical buildings and hospitals, as well as buried pipeline network systems and bridges). Soil liquefaction, frequently associated to these events, has been one of the most dramatic and significant causes of damage to engineering infrastructures and human losses, namely recently in the 2011 Great East Japan, in 2010-11 Canterbury-New Zealand earthquakes and in 2012 Emilia-Romagna, Italy. Loss of residential buildings and damage to infrastructures, such as bridges (especially abutment supports), buried pipeline networks (water supply and wastewater systems, gravity pipes, undulation of road surface and relative movement of manholes, failure of joints and connections) severely compromised services and assistance to populations.
In Portugal, the centre and south regions, densely populated areas with the highest seismic risk, are laid over loose alluvial sandy deposits, which need to be carefully labelled in terms of risk level zonation. This susceptibility to cyclic mobility and liquefaction has already been identified, yet not systematized, thus justifying research based on in situ and laboratory studies of local sands, silty-sands or even non-plastic sandy-silts, in view of a fundament evaluation of their sensitivity to liquefaction. An inexpensive yet effective protocol is urgently due to increase safety when designing in those areas. There is a need for cost-effective seismic protection solutions that can be economically adopted to safeguard infrastructures and/or residential structures, towards mitigating the impact and effects of seismic events, including the associated damage and fatalities. Portuguese codes still lack a clear app  |
Summary
Earthquakes are one of the most destructive natural phenomena. The increasing frequency and severity of seismic activities poses a serious threat to buildings and physical assets located in vulnerable locations, including critical infrastructures (i.e. public buildings, such as government offices, transport stations, terminals, historical buildings and hospitals, as well as buried pipeline network systems and bridges). Soil liquefaction, frequently associated to these events, has been one of the most dramatic and significant causes of damage to engineering infrastructures and human losses, namely recently in the 2011 Great East Japan, in 2010-11 Canterbury-New Zealand earthquakes and in 2012 Emilia-Romagna, Italy. Loss of residential buildings and damage to infrastructures, such as bridges (especially abutment supports), buried pipeline networks (water supply and wastewater systems, gravity pipes, undulation of road surface and relative movement of manholes, failure of joints and connections) severely compromised services and assistance to populations.
In Portugal, the centre and south regions, densely populated areas with the highest seismic risk, are laid over loose alluvial sandy deposits, which need to be carefully labelled in terms of risk level zonation. This susceptibility to cyclic mobility and liquefaction has already been identified, yet not systematized, thus justifying research based on in situ and laboratory studies of local sands, silty-sands or even non-plastic sandy-silts, in view of a fundament evaluation of their sensitivity to liquefaction. An inexpensive yet effective protocol is urgently due to increase safety when designing in those areas. There is a need for cost-effective seismic protection solutions that can be economically adopted to safeguard infrastructures and/or residential structures, towards mitigating the impact and effects of seismic events, including the associated damage and fatalities. Portuguese codes still lack a clear approach to liquefaction hazard zonation. The introduction of such techniques would provide guidelines for implementation of such solutions to the EU building code applicable to earthquake-prone regions (Eurocode 8, EN1998).
The studies proposed in this project will focus on the definition of practical methodologies useful for areas where funds for more rigorous procedures may not be available. The approach will utilize in situ tests which can clearly identify liquefaction-prone deposits, based on the results treated in explicit indexes, generating a rapid and clear liquefaction susceptibility classification. Experimental sites will be selected after qualitative information on soil state conditions, low density and significant thickness of granular deposits. The evaluation of the ground-shaking hazard will evidence areas where thick, loose/soft deposits likely to amplify and increase the duration of ground motion can be found, and identify areas where seismic risks are strongly associated to liquefaction. Combining the two maps, an integrated liquefaction hazard zonation map will be produced, providing an improved characterization of the soil capacity to resist liquefaction. Recent works from FEUP geotechnical group of CONSTRUCT have confirmed that liquefaction predictability of granular soils can be essentially addressed by Critical State Soil Mechanics (CSSM) theory, both from static/monotonic loading and cyclic loading conditions, but some limitations were identified (fines content, soil fabric, ageing overconsolidation or cementation, stress state and Induced stress path) which will be further addressed in these studies. In situ testing for estimate of the cyclic resistance ratio CRR is quite controversial, with distinct perspectives on the advantages of the available methods based on penetration, dilatometer or pressuremeter test results, or seismic wave analysis from geophysical surveys. Besides being only applicable in the field, except for the latter which can be reproduced in the laboratory, these procedures are mostly semi-empirical, limiting its generalization for an accurate interpretation of soil instability. In order to clarify the reasons for such differences, the experimental program will also associate high-quality sampling; for that, the project aims to implement in Portugal the novel technique of the "gel-push sampler". The collected high-quality samples will be tested in laboratory in advanced apparatuses (cyclic triaxial, cyclic direct simple shear, torsional, with shear and compression wave measurements) to identify some of the factors that control soil behaviour. Numerical modelling of specific site conditions will also be done, based on the fundamental parameters deduced from these tests, confronting distinct approaches to deal with instability, such as Stress-Density (SD), SANISAND, new UPC (Barcelona) and "PM4Sand" (UCDavies) models, all supported by the international consultants who will be working in the project. |
| Results: |
Relativamente às tarefas T1, T2, T3, a seleção de campos experimentais foi conseguida, com base na informação geológica e geotécnica disponível e que foi suficientemente exaustiva (singular no âmbito nacional) para se produzir critérios confiáveis para o estabelecimento dos protocolos que viriam a ser definidos para avaliação de liquefação origem sísmica nos locais escolhidos pela sua perigosidade, nomeadamente que contivessem significativas camadas de solos liquidificáveis pelo seu potencial (suscetibilidade) e perigosidade (hazard). Para tal foram estudados, após levantamento dos registos de ocorrências anteriores em sismos passados, com enquadramento das condições geológicas, e em zonas habitadas ou dotadas de infraestruturas relevantes. Para tal, realizou-se um exaustivo trabalho na procura e recolha do maior número possível de relatórios de prospeção geológico-geotécnica existentes, de modo a poder identificar fundamentadamente as zonas com maior interesse do ponto de vista dos critérios de seleção (Viana da Fonseca et al, 2016, Saldanha, 2017, Alves, 2017, Ferreira et al., 2019, Molina-Gómez et al., 2019, Viana da Fonseca et al. 2019).
desenvolveram-se os trabalhos de prospeção geológica, geotécnica e geofísica no segundo campo experimental, designado Norte de Benavente. A campanha de prospeção (na LZVFX) incluiu duas longas sondagens (próximo de 70m) com ensaios SPT contínuos e amostragem em furos gémeos com o sistema Mazier (recolha de 24 amostras de qualidade superior em profundidade), tendo sido preparados esses furos com encamisamento específicos para viabilizar a realização de dois perfis de ensaios sísmicos entre furos (CH – “cross-hole”). Nesse mesmo “sitio experimental” foram realizados mais 21 CPTU (ensaio de penetração estática com piezocone) e 10 ensaios dilatométricos planos espaçados de curto (DMT) que viriam a contextualizar estes solos aluvionares e marinhos da bacia do baixoTejo e assim proceder a correlações paramétricas de grande valor, dada a sua representatividade (Viana da Fonseca et al. 2019, Ferreira et al. 2019a, b). Na zona norte de Benavente, próximo do Rio Tejo onde há registos claros de liqufação de solos no grande sismo de 1909, foram realizados duas sondagens (até ao firme) geminadas com SCPTU (ensaio de penetração estática com piezocone com módulo sísmico) e ensaios dilatométricos planos espaçados de curto e também equipado com o módulo sísmico (SDMT), onde foram recolhidas amostras o sistema inovador Dames & Moore (31 amostras de qualidade elevada) e outras seis sondagens incidindo sobre os horizontes liquidificáveis – reconhecidos por aqueles ensaios precedentes - onde foram recolhidas 29 amostras de qualidade “única” com o sistema avançado e raro Gel-Push, em particular a sua versão para solos muito sensíveis (G-PS). Estes ensaios são identificados no Anexo A (Viana da Fonseca et al. 2019 a), b e c, Ramos et al.2019 a, b, c e d) Esta campanha foi ainda completada com alguns ensaios geofísicos de superfície, reconhecidamente ajustados para o mapeamento da bacia em termos geotécnicos e, sobretudo, para a caracterização das ações sísmicas presentes nos horizontes sedimentares qua a constituem, à luz das ações de referência (DNA – EC8 ou Share®), mas também a partir do de um levantamento acurado de do firme sísmico, e da frequência principal envolvida nos solos liquidificáveis. O último trabalho que está em elaboração, apresentará uma síntese do protocolos obtidos. |
| Observations: |
The assessment of the risk of liquefaction of seismic origin took into account the local amplification, in 2 areas that are very representative of situations of great danger to this phenomenon (in the lower valley of the Tagus River, in the greater Lisbon area) and in an intermediate area in the Center of the country , in Aveiro, with large thicknesses of looser, submerged and more or less fine soil deposits. This resulted in several recommendations for the application of protocols for soil characterization and assessment of the risk of liquefaction of seismic origin (expressed in publications and publications), based on more adjusted / optimized in situ test results within a framework based on interpretation tools innovative, as well as when necessary (as is the case of more demanding numerical models in more sensitive critical infrastructures) in laboratory tests, both conventionally and advanced. One of the goals achieved and even surpassed was the demonstration of the feasibility of obtaining high quality in highly susceptible and liquefiable soils using very advanced, complex and rare techniques (the GEL-PUSH SAMPLER which was used in Portugal for the first time in a world reference system and RARE confirmed it) and the possibility of using a much less complex and less expensive system (the DAMES & MOORE sampler) with similar performance, as demonstrated. Its pioneering use by the company Teixeira Duarte, which won the tender for the provision of services, enabled it for this purpose, which is also an added value of the project, in terms of the integration of knowledge of applied applied research from a center of investigation by FCT (CONSTRUCT), at FEUP, in companies providing qualified services. |