Publications

Soil water content measurement is crucial during compaction control of embankments. The current techniques used to measure the soil water content in the field are outlined, and their advantages and limitations are indicated. Most techniques require destructive sampling and yields late results, or involve expensive equipment and are hard to set up. Low-cost capacitive and resistive moisture sensors entered successfully in last decades in agronomy applications to automatize crops irrigation. The purpose of this study is to identify whether these sensors are reliable to be used in geotechnical engineering and, in particular, to what extent can they aid compaction control of embankments. Three resistive sensors and two capacitive sensors are tested on five types of soils prepared with a wide range of water contents. The experimental procedures are described, and the sensors output data are compared with water contents obtained from the oven-drying technique. A new device that allows calibration of the sensors on compacted soils is developed. Soils characteristics that can influence moisture measurement using capacitive and resistive sensors are also explored. Test results suggest that some of the sensors can estimate the soil water content on compacted fine grained soils, when proper calibration procedure is successfully achieved. Sensors accuracy tend to increase as the soil void ratio decreases. Such sensors may be useful for expedite measurements, especially, when later counter-prof is available, or when a wide interval for the water content is acceptable.

The Discrete Element Method (DEM) has been increasingly used to study the behaviour of rock. Despite theadvantage of classical DEM formulations in using simple interaction laws to model fracture initiation and propagation, they have limitations to properly simulate brittle rock behaviour. The code cannot predict the highvalues of unconfined compressive strength/tensile strength (UCS/TS) ratio associated with non-linear failureenvelopes, as observed for hard rock, such as granite, unless significant modifications are made. This paperproposes and implements a clumped-particle model into a two-dimensional DEM code. The increase in theinteraction between discrete elements, which locally increases the density of interparticle bonds, can improvethe results to obtain the desired values of UCS/TS ratio. This approach seems able to significantly increase both the potential and the predictive capabilities of DEM for rock modelling purposes. The novelties introduced in this work are the presentation of a numerical procedure to determine the equivalent micro-mechanical properties of intact rocks and, aware of a gap in our knowledge, the characterisation of uncertainties that a clumped-particle model introduces in the numerical results. A series of numerical simulations, including uniaxial compression and direct tension tests, were carried out, by varying the relation between the clump and the minimum particle radius, using the Monte Carlo simulation technique. The results were compared with experimental data on Lac du Bonnet granite, from the bibliography, which allowed to determine the equivalent micro-mechanical properties. Results, from a simulation using a core sample of Lac du Bonnet granite, show that the variance in the values of the mechanical properties calculated decreases with the decrease in the particle radius, but the influence of the clump size on the behaviour requires the execution of a considerable amount of simulations to achieve results with an acceptable relative error of 5%. Nevertheless, the mechanical behaviour obtained from DEM simulations was in good agreement with the experimental data and the model captured both the tensile and the unconfined compression strength values.

An experimental study on internal erosion of coarse-grained soils collected from the Rhine River is presented. The tests performed on laboratory column aim to assess the potential of such soils to suffusion and to characterize their stability and the variation of the soil physical parameters during the suffusion process. An experimental device (large vertical column with 60 cm of height and 26 cm of diameter) has been developed, which allows the application of upward flow to noncohesivesoils under controlled hydraulic loading. The investigation of the parameters affecting the suitability of the soilsto suffusion leads to the identification of the hydraulic gradient that initiates the migration of particles to the outlet. The results show an increase in permeability, which is related to the migration and the washing out of fine particles in the upper layer. The particle size distribution of the downward soil layer after test is performed, and the analysis corroborates the localization of particles suffusion. The grain size analysis of the outlet shows that eroded particles are smaller than 500 lm and their size rather increases with increasing hydraulic load. Usual methods based on geometrical criteria proved to overestimate the susceptibility to suffusion of soils from the Rhine, and, therefore, one consider that, for such soils, it is preferable to carry out laboratory tests to evaluate the suffusion process.

Soil-rockfill mixtures (SRMs) are economical and environmentally friendly materials. Due to the absence in theliterature of constitutive models specifically developed and tested for SRMs, a new constitutive model, theSubloading Surface Rockfill Model, is presented. This model allows the occurrence of plastic strains inside the yield surface, inducing a smooth elastic/plastic transition. The results of experimental tests for different coarse fractions (CF) of several SRMs performed on samples from Odelouca Dam are compared with those obtained with this model. The model was able to reproduce reasonably well the response of SRMs considering the intrinsic variability of the tested specimens.

A new methodology was developed to perform computer simulations of crushable rockfill particles using the dis-crete element method. Rockfill was modelled using a clump logic, responsible for providing a statistical and spatial variability in the strength and shape of the particles. Clumps have a major advantage of severely decreasing the number of contact equations to be solved in the model, resulting in less computer time. A series of single-particle crushing tests and an oedometer test were simulated using crushable particles and were in agreement with experimental data. A comprehensive study of the brittle failure of single-particle crushing tests is presented.

In order to improve the rather insufficient knowledge about the hydromechanical behavior of soil

The limitation of the progression of internal erosion in zoned dams, potentially caused by an upstream zone built of coarse, well-graded soils with non-plastic fines, is assessed using a new test cell. This device allows two types of tests to be conducted: the flow-limiting erosion test (FLET) and the crack-filling erosion test (CFET), which are designed to study the isolated influence of the flow-limiting action and the crack-filling action, respectively. The specimen is subjected to water flow along a hole drilled in the core and the upstream zone. In the CFET, the specimen additionally includes a downstream filter. Three upstream materials with non-plastic fines, a core and a filter are examined. The results of nine FLETs and nine CFETs are presented and analysed. The FLETs show the clear influence of the compaction water content, fines content and gravel content of the upstream soils in their capability to provide the flow-limiting action. The CFETs show that the specimen using the coarsest upstream soil (with 21% non-plastic fines) compacted on the dry side is capable of stopping the progression of erosion, enabling a partial crack-filling action. In all other test conditions, the filtering mechanism due to erosion of the upstream soil provides an important limitation of the erosion process. Based on the tests, practical recommendations to assess the influence of upstream zones on the limitation of internal erosion are proposed.

The paper presents the main results of a research study into the crack-filling ability of granularmaterials located upstream of an erosion path in the core of a zoned dam. Upstream crack fillers areusually considered in dams located in zones of high seismic activity, as a redundant element, should acrack develop in the core and the downstream filter fail to retain the eroded particles. Uniform soilsof fine-sand size are highly effective at filling cracks and stopping the progression of erosion; however,they can be significantly expensive. In the interest of reducing the costs of their overuse, anexperimental investigation is conducted of the extent to which gap-graded sandy gravels that arenaturally present during the construction of dams can safely provide the crack-filling action. It wasconcluded that the sand content of the upstream material that is susceptible to suffusion, and itsrelation with D15F of the filter, is critical for rapid crack filling to occur. Other parameters influencingcrack-filling ability are the gravel content, the fines content and the type of the fines in the upstreamsoil. Practical rules to estimate the likelihood of crack filling by an upstream granular material beingeffective at stopping the progression of internal erosion along a concentrated leak in zoned dams arealso proposed.

A new laboratory test, the crack-filling erosion test (CFET), was developed to study crackfilling during the progression of internal erosion in the embankment of zoned dams. Crackfilling involves the transport of eroded material from an upstream zone, through a flaw inthe core, which is then retained by a downstream granular layer. In the CFET, the specimencomprises a core, an upstream shell material, and a downstream filter layer. These arecompacted inside a test apparatus made up of several pieces. The specimen is subjected towater flow through a predrilled hole in the core to simulate a concentrated leak. Sevengranular upstream materials, two core soils, and two granular filters are examined. Followingan extensive testing program, experimental observations and physical descriptions arepresented. Three main types of pattern behaviors are identified: rapid crack filling withalmost

A new laboratory test, named the flow limitation erosion test (FLET), has been designed anddeveloped to study upstream flow limitation during the phase of progression of internalerosion in the embankment of zoned dams. Upstream flow limitation may occur because ofthe presence of the shell or a transition zone upstream of a cracked core. In the FLET, thesoil specimen is composed of core and upstream shell materials. These are compactedinside a test apparatus made up of several pieces assembled in steps. Then the soilspecimen is subjected to water flow through a predrilled hole in the core material tosimulate a concentrated leak, initiated, for example, by large differential settlement orhydraulic fracture. In most tests, the hole is also drilled in the upstream material to simulatethe scenario in which the mechanism causing the flaw in the core is also likely to affect theupstream zone. Combinations of the same core material and several types of coarse-grainedupstream materials (broadly graded and gap-graded soils) are tested for a range ofcompaction conditions and hydraulic loads. It is shown that FLET is capable of assessingwhether there is upstream flow limitation and whether the internal erosion process stops,shows a trend of slowing down, or progresses. Upstream flow limitation is shown to bedependent on the fines and gravel content, fines plasticity, and compaction water content ofthe upstream material. In the particular case of the tested gap-graded soils, it is shown to bealso dependent on the initial gradient along the upstream material.

O estudo experimental apresentado visa a avaliação do comportamento erosivo de solos grossos de granulometria descontínua. Em particular é avaliada a suscetibilidade deste tipo de solos sofrerem fenómenos de erosão interna por sufusão, quando sujeitos a um escoamento vertical ascendente. Foram ensaiados laboratorialmente seis solos granulares sem fração de areia média a grossa. Quatro destes solos não têm finos, um tem 5% de finos não plásticos e um tem 5% de finos com alguma plasticidade (índice de plasticidade de 14%). A aplicação dos métodos empíricos disponíveis na literatura para avaliar a estabilidade interna dos solos sugere que a maioria dos solos selecionados é internamente instável, ou seja, suscetível a sufusão. Os ensaios de percolação com fluxo ascendente foram conduzidos em provetes cilíndricos com seção circular de 200 mm de diâmetro e com 150 mm de espessura. Durante um ensaio o gradiente hidráulico vertical aplicado ao provete é aumentado sequencialmente com pequenos incrementos de perda de carga. A observação visual do topo do provete, juntamente com a análise da evolução do caudal de descarga, permite determinar os gradientes que originam a erosão das partículas mais finas e que conduzem ao desenvolvimento de sufusão no provete. Um fenómeno de

A barragem de Montesinho está situada no parque natural da serra de Montesinho, a cerca de 7 km a norte da povoação de Soutelo, no distrito de Bragança, tratando-se de uma barragem de enrocamento, com uma laje de betão armado a montante, como órgão impermeabilizante. O aterro tem cerca de 35,0 m de altura máxima e cerca de 310 m de desenvolvimento. O reservatório criado pela barragem destinase ao reforço do abastecimento urbano de água ao concelho de Bragança, onde anualmente, na estiagem, ocorrem períodos de grande carência hídrica. A construção da barragem foi acompanhada pelo LNEC tendo-se, nesse contexto, desenvolvido um modelo tridimensional de elementos finitos. Este modelo apresentou uma boa concordância e uma previsão de deslocamentos verticais compatível com o comportamento observado nesta fase. No presente artigo, descreve-se o sistema de observação da barragem e apresentam-se as leituras obtidas durante a fase do primeiro enchimento, procurando-se aferir se o mesmo modelo também é adequado para a simulação desta etapa.

The crack-filling action in zoned dams, by a granular upstream zone located upstream of a damaged core, was investigated experimentally using the Crack-Filling Erosion Test (CFET). The CFET allows testing specimens with three distinct zones: the upstream zone, the core and the downstream filter. The results of a series of laboratory tests are presented. A total of 34 tests were conducted combining 6 coarse-grained (gap-graded) upstream materials, 2 core soils, and 2 granular filters. The results of the CFETs showed that the crack-filling action is mainly controlled by some of the properties of the upstream zone and of the filter. Core soils with moderately slow erosion, or less erodible, should not have an influence on the crack-filling action.This is so mainly because the filling mechanism should occur over a very short period. The factors influencing the crack-filling by an upstream material are addressed, and some rules which give dam engineers a tool for decision-making about the potential of a upstream material to limit progression of erosion in concentrated leaks are indicated.

O comportamento dos materiais de enrocamento é fortemente condicionado pela resistência ao esmagamento das suas partículas. A resposta deformacional de um provete de ensaio é em grande parte devida à quebra das partículas. Como tal, torna-se importante caracterizar mecanicamente os fragmentos rochosos com o intuito de prever o comportamento estrutural de aterros de enrocamento. Recentemente, tem surgido um crescente interesse no estudo da influência da sucção no comportamento do material enrocamento e, como tal, julga-se importante caracterizar esta influência na quebra das partículas. Este artigo apresenta vários ensaios de esmagamento realizados sobre partículas de granito isoladas, de várias dimensões e para vários valores de sucção, onde se diferenciam os mecanismos de quebra de irregularidades e quebra completa da partícula. Os resultados são depois analisados e comparados, recorrendo à função de distribuição de Weibull.

A resposta deformacional de um provete de ensaio resulta na rotura dos elementos derocha, quando as tensões de contacto ultrapassam a resistência ao esmagamento, ou deum rearranjo das suas partículas, até se atingir um estado de equilíbrio. É sabido que certosaspetos do comportamento de enrocamento, como a compressibilidade e resistência aocorte, dependem da tensão de confinamento e que essa dependência é em grande partedevida à quebra das partículas. Recentemente, tem surgido um crescente interesse noestudo da influência da sucção no comportamento do material enrocamento e, como tal,julga-se importante caracterizar esta influência. Este artigo apresenta o desenvolvimento deequipamento de aplicação de sucções no edómetro de grandes dimensões existente nolaboratório. Apresentam-se ainda os resultados, quer em termos de análise dadeformabilidade do material mediante as diferentes condições, quer em termos de evoluçãoda granulometria do material. Após análise dos resultados, a eficiência do equipamento deaplicação de sucções.

This paper describes the setup of a finite element method (FEM) model for thethree dimensional simulation of the construction of a concrete face rockfill dam andfilling of the its reservoir using the Code-Aster code. The prototype of the study is the36.5 m high Montesinho dam, located in the north of Portugal near the Spain border,witch is finishing its construction, at the time of the paper writing. The dam is located inthe Sabor river in the Montesinho Natural Reserve and it is a concrete face rockfill dam.Its main purpose is to provide water supply to Bragança town reinforcing the currentreserve of the Serra Serrada dam located 3 km west of Montesinho, which is not sufficientto supply Bragança during a normal summer. Due to the fact that the dam is located inMontesinho Natural Reserve, which is a very important and sensitive ecological reserve,very special measures has been taken by the dam owner

The behavior of rockfill may be simulated using the discrete element (particle) modelling. Although its main advantage consists of not requiring the formulation of complex constitutive models, it requires extensive calibration to determine the particle

The paper starts by presenting a new laboratory test cell developed to study the progression of internal erosion in zoned dams. The aim of the equipment is to study the influence of zones located upstream of a central core, in the limitation of the progression of internal erosion through cracks in the core. In particular, the test cell allows performing the Flow Limiting Erosion Test (FLET) and the Crack Filling Erosion Test (CFET), for the study of the upstream flow limiting action and of the crack-filling action, respectively. Several FLET

This paper presents an experimental study aiming at the evaluation the suffusion behaviour of coarse gap-graded soils, considered as potential upstream crack-fillers in zoned dams. Six granular gap-graded soils missing the medium-to-coarse sand fraction have been examined. Four soils have no fines, one has 5% of non-plastic fines, and one has 5% of clayey fines (with plasticity index of about 14%). The use of available methods to assess internal stability of soils suggests that the majority of the selected soils are highly susceptible to suffusion. Testing has been carried out in the Upward Flow (UF) seepage test. A cylindrical seepage cell is used to impose vertical flow, from the bottom to the top, along a soil specimen with 200 mm-diameter and 150 mm-thick. During an UF test, the hydraulic gradient in the soil specimen is slowly increased in steps. The observation of the erosion behaviour at the top surface of specimen, together with the evolution of the discharge flow rate, allows determining the hydraulic gradients causing initiation of erosion on top of the specimen and development of suffusion in the soil. A

Two mechanisms limiting the progression of internal erosion in zoned dams, potentiated by the presence of materials located upstream of a damaged core are investigated. These are the flow limiting and crack-filling actions. The former is related with the ability of the upstream soil limiting the flows passing through a flaw in the core. The latter involves transport of particles from the upstream zone into a flaw in the core up to a downstream granular zone. A new apparatus is developed from scratch. It allows carrying out two innovative laboratory tests: the Flow Limitation Erosion Test (FLET) and the Crack Filling Erosion Test (CFET). Following an extensive testing programme on twelve upstream materials, two cores, and two downstream filters, experimental observations and physical descriptions are presented. The potential soil behaviour patterns are described. The flow limiting action is governed by grading, plasticity and compaction characteristics of the upstream soil. Crack filling by granular soils is a rapid mechanism, being governed mainly by the compatibility of the washed in material from the upstream soil with the downstream filter. In general, the higher the sand and the lower the fines content of the upstream soil, and the lower the effective grain diameter D15F of the filter, the higher the likelihood of the crack-filling action to occur.

Como é bem sabido, a realização de barragens, a par dos reconhecidos benefícios de váriaordem resultantes da sua exploração, pode envolver danos potenciais para as populações ebens materiais e ambientais na sua vizinhança, pelo que se torna indispensável assegurarum controlo da segurança dessas obras. Esses danos estão sobretudo associados aos efeitosda onda de cheia gerada pela rotura da estrutura. A que há que adicionar naturalmenteos custos associados à destruição da própria estrutura.

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Two mechanisms limiting the progression of internal erosion in zoned dams, potentiated by the presence of materials located upstream of a damaged core are investigated. These are the flow restriction and crack filling actions. The former is related with the ability of the upstream soil restricting the flows passing through a flaw in the core. The latter involves transport of particles from the upstream zone into a flaw in the core, up to a downstream granular zone. A new apparatus is developed from scratch. It allows carrying out two innovative laboratory tests: the Flow Limitation Erosion Test (FLET) and the Crack Filling Erosion Test (CFET). Following an extensive testing programme on thirteen upstream materials, two cores, and two downstream filters, experimental observations and physical descriptions are presented. The potential soil behaviour patterns are described. The apparatus can assess whether erosion in the core stops, slows down, or progresses. The flow restriction action is governed by grading, plasticity and compaction characteristics of the upstream soil. In gap-graded with 5% of fines, the hydraulic loading and type of fines are critical. Crack filling by granular soils occurs rapidly, being governed by the sand and fines content of the upstream soil, and an effective grain diameter (D15F) of the filter. Rules for preliminary estimation of the likelihood of occurrence of the studied actions are also proposed.

Em Portugal serão construídas, nos próximos anos, algumas centenas de quilómetros de vias férreas de alta velocidade. As exigências associadas a estas linhas, em particular no que concerne a tolerâncias de fabrico, são, naturalmente, mais restritivas que as das linhas férreas tradicionais, onde circulam comboios de carga e de passageiros a velocidades mais reduzidas.Em diversos países tem-se verificado que a conjugação de velocidades elevadas de circulação com determinadas características dos solos de fundação conduz a fenómenos de amplificação dinâmica das deformações resultantes da circulação dos comboios.As linhas de alta velocidade, em Portugal, terão inevitavelmente de atravessar zonas onde a velocidade de circulação se pode associar com as condições desfavoráveis das fundações criando os fenómenos dinâmicos referidos.O presente Programa de Investigação situa o problema da circulação dos comboios de alta velocidade sobre solos moles, faz uma revisão dos métodos existentes para a previsão e análise do fenómeno, e analisa as medidas de mitigação existentes.Em resultado da análise do problema são perspectivadas diversas linhas de investigação que têm como objectivo: a identificação dos factores que contribuem e condicionam a geração e propagação das vibrações; o desenvolvimento de ferramentas de análise e previsão; a identificação e estudo das zonas que, estando no traçado das linhas de alta velocidade em Portugal, possuem as características que potenciam o desenvolvimento do fenómeno e, finalmente, conjugando o conhecimento resultante dos tópicos anteriores, a análise das medidas de mitigação mais adequadas para os casos identificados. Por último, é apresentado um Programa de Pós-Graduação, onde são concretizadas as linhas de investigação propostas, sob a forma de planos de enquadramento de recém licenciados, de teses de mestrado e de doutoramento.

A primeira centrifugadora geotécnica portuguesa foi recentemente instalada (1994) noLaboratório Nacional de Engenharia Civil. Para tanto estabeleceu-se um plano de acçãovisando três objectivos principais. Por um lado, e dada a natureza pioneira à escala nacional daaplicação em causa fundamentar a técnica de modelação física proposta. Por outro,materializar os meios necessários à exploração do novo recurso. Finalmente, aplicar a técnicade modelação física, no âmbito de um plano de investigação que permitisse ilustrar as suaspotencialidades. Esta dissertação constitui o corolário desse programa de acção, reflectindo ostrês objectivos programáticos estabelecidos.

RESUMOO presente trabalho visa fundamentalmente apresentar novas propostas na modelação dedeterminados efeitos característicos de aterros, especialmente quando se trata de aterros deenrocamento. Os efeitos visados, o colapso e a fluência manifestam-se pelo aumento dasdeformações dos aterros nomeadamente de barragens. No primeiro caso, as deformações sãoprovocadas pela molhagem do material e ocorrem de forma súbita, podendo implicarimportantes perdas de folga das barragens. No segundo, as deformações ocorrem de formadiferida no tempo e, por vezes, representam uma parcela significativa da deformação total.Passa-se em revisão os modelos de comportamento mecânico habitualmente utilizados nadescrição do comportamento dos materiais geotécnicos em modelos matemáticos, bem comoas técnicas e métodos numéricos, indispensáveis para a abordagem dos problemas específicosdas barragens.Propõe-se uma nova abordagem para modelar o colapso baseada na variação progressiva dosparâmetros das leis constitutivas. Apresenta-se ensaios de determinação das características decomportamento de materiais de enrocamento permitindo simultaneamente o estudo dadeformação de colapso. Desenvolvem-se técnicas ensaio que possibilitam nomeadamente, oestudo do comportamento do material à repetição de ciclos de molhagem-secagem e asimplicações que estes ciclos podem ter na deformação de colapso.Considera-se que a fluência pode ser tratada de forma análoga ao colapso excluindo a escalade tempo do fenómeno. Realizam-se ensaios que, à luz do modelo adoptado, permitem aferiros parâmetros que controlam a deformação de fluência no tempo.Os modelos desenvolvidos são aplicados ao estudo de dois casos reais de grandes aterros deenrocamento. No primeiro caso, apresenta-se uma retroanálise do comportamento dabarragem de Beliche, concluindo-se haver uma boa concordância entre os valores resultantesda observação da barragem e os resultados dos modelos propostos. O segundo caso, refere-sea um aterro de estrada com altura máxima de 40 m que está compreendido na empreitada deconstrução da barragem de Odeleite. Neste caso não se dispõe ainda dos resultados daobservação dos deslocamentos e, por esse motivo, os valores apresentados constituem umaprevisão de comportamento.

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Relato da visita de 22 de janeiro de 2024 à Linha do Oeste por parte do Departamento de Geotecnia