Papers by António Viana da Fonseca
This paper will summarize the geotechnical characterization studies conducted for the design and ... more This paper will summarize the geotechnical characterization studies conducted for the design and subsequent back-analysis based on real time monitoring of a strutted excavation in Porto metro network. This region is geologically dominated by heterogeneous weathered granite masses with deep residual soils profiles. Moreover, these saprolitic soils exhibit, by their nature, a particular behavior characterized by very sensitive and weak relic micro-structures, due to their specific genesis. This study has included the interpretation of a significant volume of in situ test results, triaxial tests over undisturbed samples and monitoring data, giving rise to specific correlations between testing and design parameters. Available geodata recoiled enabled a back-analysis by a FEM commercial code (PLAXIS) of a well instrumented section of the strutted supported excavation, which was calibrated taking into account the derived correlations and the deformability behavior of this specific geotec...
A large set of undrained compression triaxial tests was carried out on different types of cohesio... more A large set of undrained compression triaxial tests was carried out on different types of cohesionless soils, from sands to silty-sands and silts. Shear wave velocity measurements were carried out alongside. These tests exhibited distinct state transitions ranging from flow liquefaction to strain softening or strain hardening. With the purpose of defining a framework to assess soil liquefaction, it was found that the ratio between the shear wave velocity (VS0) and the peak undrained deviatoric stress, qpeak, VS0/qpeak, could be accurately used to define a boundary between liquefaction and strain hardening for sands, and between strain softening and strain hardening for silty-sands and silts. Since this ratio is a function of the tested material, it was also discovered that the prediction of these boundaries could be made as a function of soil grading, namely via the coefficient of uniformity, CU. Despite not being regarded as a strong geomechanical parameter, CU is easily determined...
Soil Dynamics and Earthquake Engineering
Sustainability
Slags and rubber from end-of-life tires represent a liability to the steel and tire industry, cau... more Slags and rubber from end-of-life tires represent a liability to the steel and tire industry, causing economic and environmental problems that are difficult to manage. Transport infrastructures can use these industrial by-products instead of extracting natural raw materials, but the adequate mechanical performance of the materials needs to be assured. This paper addresses the mechanical behaviour of slag–rubber mixtures in the laboratory with CBR, monotonic and cyclic triaxial tests. In addition, light falling weight deflectometer tests were also performed in a physical model. The results were analysed to meet technical specifications from Brazil, Portugal and Australia using railway sub-ballast layers, capping layers or road pavement layers as the base and sub-base to identify the applicability range of slag–rubber mixtures for transport infrastructures. Concerning the analysed parameters, it was demonstrated that slag–rubber mixtures can show resilient behaviour and strength adequ...
Bulletin of Earthquake Engineering
Acta Geotechnica
This work stems from the need to validate a technique for a reliably measurement of the degree of... more This work stems from the need to validate a technique for a reliably measurement of the degree of saturation (Sr) in deposits composed of sandy soils to improve their liquefaction resistance. The estimation of the degree of saturation of soil can be conducted by assessing the P-wave velocity (Vp), due to it values sharply increase near to the full saturation condition. P-wave measurements are comparable for in situ and laboratory procedures, offering prominent advantages for practical implementation. This paper presents a series laboratory results obtained from bender element tests conducted on a partially saturated monogranular sand. As a first approach, these tests were interpreted in the time-domain, showing how the interferences among the generated waves can significantly affect results and mask the actual degree of saturation in the specimen. However, a new processing of the output signal was carried out in the frequency-domain to accurate identify the wave propagation time. Mo...
Soils and Rocks
The paper deals with the analysis of static loading tests carried out in 3 different types of pil... more The paper deals with the analysis of static loading tests carried out in 3 different types of piles: bored piles with temporary casing, continuous flight auger, CFA, piles (bored and CFA piles with circular section - nominal diameter Ø600 mm) and driven piles (with square section - width 350 mm). These piles were installed in the CEFEUP/ISC’2 experimental site, located in the Campus of the Faculty of Engineering of the University of Porto (Portugal), in a contact zone between the gneissic rocks and the granite mass. After a brief geological and geotechnical site characterization, the paper presents a detailed description of the piles and the instrumentation installed in two of them. Previous analyses of the test data are summed up, emphasising the difficulties in determining the residual loads resulting from the installation processes and the unloading and the reloading cycles applied to the static loading tests. This paper aims to quantify these locked-in toe residual loads, using ...
This paper provides a simple preliminary procedure for estimating the performance of a building o... more This paper provides a simple preliminary procedure for estimating the performance of a building on liquefiable soil. The procedure directly accounts for damage related to ground shaking and in-directly accounts for settlements. Additionally, it also considers the change in shaking demand and changes to the natural vibration modes of the systems due to liquefaction. The proposed procedure makes use of a displacement-based assessment procedure that considers nonlinear soil-foundation-structure interaction and extends it to include the effects of liquefaction. The extensions rely on several assumptions about the behaviour of the soil, site response and the structure, which require further research to improve the robustness of the assessment. Two small studies are conducted: one explores at what time the peak displacement of a system occurs during shaking, and the second explores the potential changes in site amplification due to liquefaction, which provide some justification to the pro...
Geotechnics, 2022
Earthquake-induced liquefaction is one of the major causes of building damage as it decreases the... more Earthquake-induced liquefaction is one of the major causes of building damage as it decreases the strength and stiffness of soil. The liquefaction resistance of soils increases significantly as the degree of saturation decreases, making soil desaturation an effective measure for the mitigation of this phenomenon. This paper presents a comparative analysis of liquefaction resistance of an alluvial sand from Aveiro (Portugal) under fully and partially saturated conditions. For this purpose, an in situ characterisation based on CPTu and a laboratory series of cyclic triaxial tests were carried out. The cyclic triaxial tests were conducted under undrained conditions on remoulded specimens with different degrees of saturation, including the full saturation. On the other hand, the triaxial apparatus was instrumented with Hall-effect transducers to accurately measure the strains during all testing phases. In addition, it was equipped with piezoelectric transducers to measure seismic waves ...
Numerical Methods in Geotechnical Engineering IX, 2018
This paper presents a framework for efficiently producing engineering research in a global collab... more This paper presents a framework for efficiently producing engineering research in a global collaborative effort in a rigorous scientific manner. The proposed framework reduces subjective analysis, automates several mundane research tasks and provides a suitable formal structure for efficient information sharing and collaboration. The implementation of the framework involves multiple research groups setting up different web-servers that can perform the steps of the scientific method and automatically determine the quality and value of new research by directly communicating between servers via public and private application programming interfaces (APIs) using a set of object-oriented protocols. The automation of many mundane research tasks (e.g. data manipulation), would allow researchers to focus more on the novel aspects of their research efforts. The increased clarity around the quality and value of research would allow the research efforts of individuals and available research funding to be better disbursed. The paper discusses the major aspects of the scientific method, object-orientated programming, the application of the proposed research framework for experimental/analytical/numerical engineering research, some of the potential benefits and drawbacks, as well as the current state of implementation.
Geotechnical Testing Journal, 2021
Bender elements (BEs) have become a routine geotechnical laboratory tool for seismic wave velocit... more Bender elements (BEs) have become a routine geotechnical laboratory tool for seismic wave velocity measurements. Since the 1980s, this testing technique has gained popularity, currently being available in many geotechnical laboratories worldwide in a variety of apparatuses. The advantage of simultaneously measuring small- and large-strain soil stiffnesses in each device and the easiness and low-cost implementation of BE are the main reasons for their common application. Although there is already a standardized procedure for BE testing (ASTM D8295-19, Standard Test Method for Determination of Shear Wave Velocity and Initial Shear Modulus in Soil Specimens Using Bender Elements), the use of high-frequency pulses for the simultaneous measurement of compressional (VP) and shear (VS) wave velocities is not considered. In contrast, the use of high-excitation frequencies is usually discouraged, as they tend to induce spurious participation of high-vibration modes in the BE response. However, this work shows that the use of higher vibration modes can be advantageous to evaluate P-wave velocities from standard BE testing. Thus, this paper presents a new approach for the concurrent measurements of VP and VS using a typical installation of BE. The new approach is first demonstrated by experimental measurements and subsequently validated using high-frequency laser vibrometer measurements of the actual BE deformation (nanometer scale) under different excitation frequencies. The laser vibrometer measurements show the displacements of the transmitter BE as a function of the input frequency in not only the horizontal but also in the vertical directions, demonstrating the generation of P-waves when higher vibration modes are excited. The measured VP values are shown to be in good agreement with the predicted values using Biot’s equations. Thus, the proposed methodology addresses the current knowledge gap in the use of BE for concurrent P-wave and S-wave velocity measurements. The generated wavelengths are large enough to travel through the soil skeleton instead of the pore water only.
Géotechnique Letters, 2021
Monitoring the curing process of mixtures produced by soil, fly ash and alkaline solution can be ... more Monitoring the curing process of mixtures produced by soil, fly ash and alkaline solution can be effectively performed by ultrasonic measurements of compression and shear wave velocities. These measurements detect the evolution of stiffness with time, as a result of alkali-activated ash reactions. Conventionally, ultrasonic testing relies on the use of a fixed input frequency, corresponding to the nominal frequency of the transducer, for which a maximum response is expected from the transducers. This procedure, however, has shown some limitations especially when applied to materials under curing, in which stiffness is changing with time. To overcome these limitations, a wide range of frequencies, from 24 to 200 kHz, was used at each of the selected curing periods for determining wave travel time, instead of a single frequency reading. The results show a clear increase in the optimum frequency with curing time, indicating that the ultrasound testing frequency should be adjusted to ac...
Bulletin of Earthquake Engineering, 2020
Large magnitude earthquakes have historically caused devastating damage to engineered structures ... more Large magnitude earthquakes have historically caused devastating damage to engineered structures as a result of permanent ground deformations induced by soil liquefaction (e.g. 1964 Niigata earthquake, 1995 Kobe earthquake, 2010-2011 Christchurch earthquakes). A relevant amount of such damages is directly connected to liquefaction induced lateral spreading. This paper deals with the capacity of concrete framed structures with shallow foundations to handle lateral spreading demands. A simplified force-displacement compatible model was developed to capture the loads on the shallow foundations and estimate the performance of the building. The key parameters of foundation embedment, foundation width and shear length of the pillar, as well as soil friction angle were identified as having a strong influence on the expected performance. The developed model was used to develop probabilistic fragility curves for a class of buildings representing two to five storeys reinforced concrete buildings. Field measurements from existing literature of the liquefaction induced lateral displacement demand from the the September 4, 2010 (Mw 7.1) and the February 22, 2011 (Mw 6.2) Canterbury (New Zealand) earthquakes along the Avon River were probabilistically quantified in relation to the distance from the river. Finally, the displacement demand and fragility curves were used to estimate the probability of exceeding the considered limit states as a function of the distance from the river.
Soil Dynamics and Earthquake Engineering, 2020
The stiffness properties of soils, particularly shear modulus and damping ratio, play a fundament... more The stiffness properties of soils, particularly shear modulus and damping ratio, play a fundamental role in predicting the ground deformation during cyclic and dynamic loading. The dynamic properties can be used for the assessment of seismic ground response and the analysis of soil-structure interaction. This study provides a detailed dynamic characterisation of two liquefiable sandy soils, which have experienced earthquake-induced liquefaction, as historically documented. The soils were collected in the greater Lisbon area, in the south of Portugal. For this purpose, a comprehensive laboratory testing programme, which included a series of bender-element and resonant-column tests, was conducted. During the study, the effects of void ratio and mean effective stress on the soil stiffness were examined, focusing on the small-strain response. Results show shear modulus degradation and damping ratio curves, at small and intermediate shear strain levels, for saturated reconstituted samples under different stress conditions. Data obtained in the laboratory of both materials were fitted into normalised models to estimate the dynamic properties for different stress and state conditions. In addition, damping ratio curves were compared against the typical bounds of quartz materials. Stress-dependent models for estimating the maximum shear modulus and threshold shear strain amplitudes of both sands are proposed in this paper. The data provided in this study are useful for numerical analyses and geotechnical design, particularly when involving dynamic or seismic approaches.
Geotecnia, 2014
RESUMO-O presente artigo refere-se à análise de um aterro sobre solos moles através do programa d... more RESUMO-O presente artigo refere-se à análise de um aterro sobre solos moles através do programa de elementos finitos Plaxis ® comparando a solução implementada (com geodrenos e pré-carga) com uma solução de tratamento em Deep Soil Mixing (DSM). Foram analisadas várias soluções alternativas em DSM, alterando o espaçamento entre as colunas, o tempo de cura, e até a existência ou não de uma plataforma de transferência de cargas. Para cada caso, os assentamentos foram aferidos e comparados verificando se satisfaziam os requisitos do caderno de encargos. Finalmente foi ainda efetuada uma análise de viabilidade económica com comparação do tempo de execução e dos custos associados às várias soluções. SYNOPSIS-In the present work an embankment on soft soil is analyzed with commercial finite element software (Plaxis ®) in order to compare the solution implemented on site (with drains and preloading) with a soil improvement solution in Deep Soil Mixing (DSM). Several alternative solutions in DSM were studied changing the column spacing, the curing time, as well as the inclusion of a load transfer platform. For each case the settlements were analyzed and compared to evaluate if the necessary requirements in terms of limit values were satisfied. Finally, a cost-benefit analysis was performed focused on the execution time and cost of each solution. PALAvRAS ChAvE-DSM, aterro sobre solos moles, modelação numérica. 1-INTRODUÇÃO O crescimento da população tem como consequência a expansão das áreas urbanizadas para zonas desocupadas, que apresentam, na maior parte dos casos, solos com fracas características do ponto de vista geotécnico, nomeadamente para a implementação de qualquer tipo de estrutura. Neste contexto, o desenvolvimento de meios tecnológicos e o aparecimento de novos mate riais de construção no século XX, entre outros fatores, permitiram descobrir várias soluções de 69 Geotecnia n.º 131-julho/julio 2014-pp. 69-94
Journal of Materials in Civil Engineering, 2016
Alkaline activation of fly ash was used to improve the mechanical performance of a silty sand, co... more Alkaline activation of fly ash was used to improve the mechanical performance of a silty sand, considering this new material as a replacement of soil-cement applications namely bases and subbases for transportation infrastructures. For that purpose, specimens were molded from mixtures of soil, fly ash and an alkaline activator made from sodium hydroxide and sodium silicate. Uniaxial compression tests showed that strength is highly increased by the addition of this new binder. The results described a high stiffness material, with an initial volume reduction followed by significant dilation. All specimens have clearly reached the respective yield surface during shearing, and peak strength Mohr-Coulomb parameters were defined for each mixture. The evolution of the microstructure during curing, responsible for the mechanical behavior detected in the previous tests, was observed by scanning electron microscopy. These results were compared to soil-cement data obtained previously with the same soil at similar compaction conditions. The main difference between both binders was the curing rate, with alkali activated specimens showing a more progressive and long-lasting strength increase. This was analyzed taking into account the chemical process responsible for the behavior of the mixtures.
Geotechnical and Geological Engineering, 2006
... The thickness of these residual saprolitic horizons may vary between few meters to more ... a... more ... The thickness of these residual saprolitic horizons may vary between few meters to more ... an accurate mapping of the spatial variability of the mechanical properties, necessary for ... of ISC'2 experimental site, comprising the application of several geotechnical and geophysical ...
Geotecnia, 2021
Ao longo da última década, as técnicas de amostragem de solos têm evoluído no sentido de reduzire... more Ao longo da última década, as técnicas de amostragem de solos têm evoluído no sentido de reduzirem o atrito na interface entre o amostrador e o solo, minimizando as perturbações e obtendo amostras de alta qualidade para caracterização laboratorial. No âmbito de um projeto de investigação focado no estudo da liquefação em Portugal (LIQ2PROEARTH) e um europeu mais global (LIQUEFACT), foi implementado um campo experimental nas zonas de Benavente e Vila Franca de Xira, no qual foram realizados diversos ensaios in situ (SPT, CPTu, DMT), com medição de ondas sísmicas (SCPTu e SDMT) em locais onde foram recolhidas amostras indeformadas. O presente trabalho apresenta a experiência com amostradores especialmente adaptados a condições difíceis, Dames & Moore e Gel-Push, em depósitos aluvionares granulares com suscetibilidade à liquefação. Os procedimentos de manuseamento e transporte adotados são descritos e o desempenho de cada metodologia é avaliada em termos de integridade material e estru...
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Papers by António Viana da Fonseca