Publicações

The proper assessment of soil thermal properties, such as thermal conductivity, assumes a particular relevance for the design of Ground Source Heat Pump systems, as it determines the heat transfer and the energy efficiency design. Multiple methods can be used for thermal conductivity estimation, however significant scatters in measurements are often reported when using different (or even the same) methods. This work presents a detailed study of the thermal conductivity and the thermal contact conductance of a reference sand tested in transient conditions, analyzing the effect of several factors, such as the heating time, degree of saturation, soil density, temperature and heat flux intensity, on thermal conductivity measurements for dry state or fully saturated conditions. To avoid measurement errors and heterogeneity effects, only three samples were prepared with different compaction ratios, and systematically tested in dry and fully saturated conditions, under different control variables (temperature, testing time, and injected heat flux). Two analytical methods based on the line source solution were used to estimate soil thermal conductivity and to assess the probe-to-soil thermal contact conductance. Significant relationships were obtained between thermal conductivity and soil state conditions and testing variables, highlighting that a heating time longer than the one usually recommended in the standards is clearly needed. Finally, this study uses measured temperature values to determine the probe-to-soil thermal contact conductance, indicating its relevance in soil thermal conductivity estimation.

This paper reports the findings of experimental studies on a novel application of a closed cell expansive polyurethane resin injection into a sand mass, regarding some common engineering properties.Previous papers on injecting expansive polyurethane resins into sand masses as mitigation measures ofdifferent hazards, e.g., liquefaction, settlements and seismic displacements, deal with the open cell sub-class ofpolyurethane resins. Seeking to make up for the shortcomings of open cell methods, the paper addresses aprototype application of a closed cell polyurethane resin for ground improvement/control on sands.A new system for the preparation of the sand-resin mixture (SRM), which mimics the field application conditions, is introduced. It allows to inject the polyurethane resin into saturated sand with a prescribed massdensity.The results of an extensive laboratory testing program are presented and discussed regarding some relevantengineering properties, e.g., Young

In this paper, capillary stresses and water retention of regular arrangements of rough spherical particlesare analysed to shed light on the effective stress in unsaturated soils. These arrangements can be usedto model soils with uniformly graded round particles such as sand as they are simpler to analyse due totheir symmetries. Capillary stress determines the effective stress in unsaturated sphere arrangementsand is highly dependent on the morphology of the soil voids. In general, it is shown that capillary stress and water retention dependence on suction and degree of saturation in regular arrangements of spheres is more complex than usually assumed with relevant implications for unsaturated soil mechanics and its effective stress. It is also shown that: (i) sphere roughness explains the observed disappearance of capillary stresses in sand with drying; (ii) the capillary stress evolution with suction (or RH) is non monotonic; (iii) it is possible to have significant capillary stresses at zero suction in regular and irregular sphere arrangements, and the Bishop

This paper addresses the topic of site characterization for the design of Shallow Geothermal Energy (SGE) systems, namely of thermoactive geostructures, which are geotechnical structures, such as piles, retaining walls and tunnel linings, also used as heat exchangers as part of closed-loop SGE systems. Such solutions, being increasingly adopted for buildings

Climate change is already being felt in Europe, unequivocally affecting the regions

In the framework of a third Tagus River crossing, through an immersed tunnel, advancedlaboratory tests were performed on its highly liquefiable foundation sand. To characterizethe cyclic behaviour of the sand and to support the use of advanced constitutive models inthe design of the tunnel, key to simulate liquefaction realistically in such a complex project,five cyclic undrained torsional tests were executed. These tests, in which imposed strainincreases progressively until and during liquefaction, considering strain amplitude levelswith a limited number of cycles, allow a more thorough study of the phase after initialliquefaction than the usual test with constant stress amplitude and the necessary number ofcycles to attain liquefaction. Additionally, they provide high quality data, essential to calibrateadvanced constitutive models. From their analysis, it is concluded, as expected, thatthe number of cycles until initial liquefaction increases with relative density and confiningpressure. Moreover, while before initial liquefaction maximum excess pore pressure amplitudeis due to sand softening and consequent pore pressure build-up, after initial liquefactionit usually happens at the first cycle, being related to an initial higher dilation tendency,before particles loose contact. Finally, the damping ratio increases until a peak value, andthen, just before initial liquefaction, generally decreases till the end of the test.

Shallow geothermal energy systems (SGES) may take different forms and have recently taken considerable attention due to energy geo-structures (EGS) resulting from the integration of heat exchange elements in geotechnical structures. Still, there is a lack of systematic design guidelines of SGES. Hence, in order to contribute towards that direction, the current study aims at reviewing the available SGES modeling options along with their various aspects and practices. This is done by first presenting the main analytical and numerical models and methods related to the thermal behavior of SGES. Then, the most important supplementary factors affecting such modeling are discussed. These include: (i) the boundary conditions, in the form of temperature variation or heat flow, that majorly affect the predicted thermal behavior of SGES; (ii) the spatial dimensions that may be crucial when relaxing the infinite length assumption for short heat exchangers such as energy piles (EP); (iii) the determination of SGES parameters that may need employing specific techniques to overcome practical difficulties; (iv) a short-term vs. long-term analysis depending on the thermal storage characteristics of GHE of different sizes; (v) the influence of groundwater that can have a moderating effect on fluid temperatures in both heating and cooling modes. Subsequently, thermo-mechanical interactions modeling issues are addressed that may be crucial in EGS that exhibit a dual functioning of heat exchangers and structural elements. Finally, a quite lengthy overview of the main software tools related to thermal and thermo-hydro-mechanical analysis of SGES that may be useful for practical applications is given. A unified software package incorporating all related features of all SGES may be a future aim.

This paper presents a thermo-viscoplastic subloading soil model with a mobile centre of homothety. The model is formulated to describe the influence of non-isothermal conditions on the stress

The behaviour of natural and artificial slopes is controlled by their thermo-hydro-mechanical conditions and bysoil

This paper illustrates the capability of a viscoplastic subloading model recently proposedin reproducing strain-rate change effects in soil. The viscoplastic model used is based onthe subloading surface concept making possible the occurrence of viscoplastic strainsinside the yield surface. After a brief description of the basic principles and constitutiverelations behind the model, a numerical simulation of an undrained triaxial compressiontest on a normally consolidated reconstituted London clay with several strain-ratechanges was performed with success. This result was obtained with a general soil modelwhich did not take into account these specific temporary effects in its formulation. Theinfluence of the strain

The soil nailing construction technique is often used to stabilise a ground mass by installing reinforcing elements (nails). The European Standard EN 14490:2010 defines general principles for execution, supervision, testing and monitoring of soil nailing. This paper presents tests results obtained in several ground nails executed in recent geotechnical works. These tests were carried out in sacrificial nails, before and during the works. As shown in this paper, the execution of the nails, the test system and test procedures affect their results quality. Thus, a critical analysis of the tests results is performed to assess the behaviour of the ground nails, framed by EN 14490:2010, in accordance with the design and contract specifications.

O projeto de investigação GeoSustained, financiado pela Fundação Portuguesa para a Ciência e a Tecnologia (FCT, PTDC/ECI-CON/1866/2021), visa estudar soluções sustentáveis utilizando sistemas geotérmicos superficiais para climatização de edifícios e infraestruturas, sob as condições climatéricas e geológicas ocorrentes na cidade de Lisboa. No contexto do projeto, serão instalados furos de monitorização contínua datemperatura no terreno em locais selecionados da cidade. Antes da colocação de séries de termopares dispostos em profundidade, serão recolhidas amostras intactas representativas das principais formações geológicas de Lisboa para ensaios laboratoriais, onde serão obtidas as suas características termofísicas, destacando-se a condutividade térmica. Esta propriedade, será também estimada por via de modelos semi-empíricos, através das frações volumétricas das diferentes fases do solo e, ainda, com base em valores, ou gamas de valores, resultantes de compilações de resultados de ensaios realizados em unidades geológicas semelhantes, disponíveis na bibliografia.Os aspetos mais relevantes deste estudo inicial relativo ao estudo das propriedades térmicas dos solos de Lisboa a diferentes escalas, que virá a fornecer importantes elementos para o futuro planeamento da cidade, são aqui descritos e analisados.

As ancoragens no terreno em estruturas de contenção, apresentam-se como

A avaliação das propriedades térmicas dos solos, em especial da sua condutividade térmica, tem assumido uma importância crescente, sendo essencial para o dimensionamento de sistemas geotérmicos superficiais. Apresentam-se neste trabalho, alguns aspetos de um estudo relativo à medição e modelação de ensaios de condutividade térmica em amostras de solo, conduzidos em regime transitório

A avaliação das propriedades térmicas dos solos, em especial da sua condutividade térmica, tem assumido uma importância crescente, sendo essencial para o dimensionamento de sistemas geotérmicos superficiais. Apresentam-se neste trabalho, alguns aspetos de um estudo relativo à medição e modelação de ensaios de condutividade térmica em amostras de solo, conduzidos em regime transitório.

A new constitutive model to reproduce the soil-water retention behaviour of unsaturated soils is proposed, able to reproduce the main drying and wetting paths, the cyclic retention behaviour and its dependence on the specific volume. The most significant aspect is the inclusion of the evolution, with the specific volume, of the degree of saturation when suction tends to zero in wetting paths considering the presence of entrapped air bubbles. The model is used to reproduce with success the drying/wetting cycles of two Pearl clay samples

In the framework of a third Tagus River crossing, through an immersed tunnel, a novel liquefaction mitigation measure, namely injection of a duromeric expansive polyurethane resin, was tested on its highly liquefiable foundation sand. Three laboratory injection tests were executed: the first consisted in injecting a central column, inside a specifically designed box filled with Tagus River sand, to characterize the properties of the sand-resin mixture (SRM); the second and third comprised injecting five separate columns each, with different replacement ratios, to measure the effect of the injection on the sand densification between columns. Aninjection rod withdrawal rate (IRWR) of 0.01 m/90 s, 0.01 m/10 s and 0.01 m/15 s was used for the first, second and third tests, respectively. Specimens were core drilled from the injection test

In this paper, the Discrete Element Method is used to study the e ect of capillary forces, in equilibrium with the ambient relative humidity, on the response of irregular arrangements of equal-sized spheres, simulating a fine uniformly graded quartz sand. The e ect on the isotropic compression was investigated by applying an increase in total stress under constant relative humidity (wet and dry) and drying under di erentconstant total stress values. The e ect of the capillary forces on the shear strength was evidenced by the simulation of the instability of a cylindrical sand column due to drying.

In the framework of a third Tagus River crossing, through an immersed tunnel, advancedlaboratory tests were performed on its highly liquefiable foundation sand, namely cyclicundrained torsional tests. The Manzari-Dafalias model, which allows simulating liquefactionon the Tagus River sand and is, therefore, central in the tunnel design, as well as thenumerical work to calibrate the model and identify its most relevant parameters, arepresented. Model parameters, their respective reference values and tests performed todetermine directly most of the parameters, are introduced. A parameter sensitivity analysis,conducted through numerical simulation of triaxial monotonic drained tests and of cyclicundrained torsional tests, implemented both for the pre-liquefaction and liquefaction phases,is described. Finally, some parameters are determined by fitting the model to the laboratoryresults.

O aumento da população mundial e as necessidades de reduzir os impactes negativos da utilização das energias fósseis, têm levado a uma crescente utilização de fontes de energia renovável nas últimas décadas. A energia geotérmica é uma dessas fontes de energia, apresentando diversas vantagens a nível ambiental e económico. Os recursos geotérmicos podem ser distinguindos em recursos de alta ou baixa entalpia. Os recursos de alta entalpia são utilizados para a produção de energia elétrica e os de baixa entalpia, maioritariamente, para climatização. Nestes últimos, estão incluídos os designados sistemas geotérmicos superficiais de muito baixa entalpia, com recurso a bombas de calor (Ground Source Heat Pump systems), que utilizam as camadas superficiais do terreno até 150m de profundidade, para extrair ou injetar calor, respetivamente nos modos de aquecimento ou arrefecimento dos edifícios. Os sistemas geotérmicos superficiais são constituídos por três partes principais, que são: o circuito primário, que é a parte do sistema que permuta calor com o solo, integrando as designadas geoestruturas termoativas, o circuito secundário, que constitui a transmissão térmica do calor no edifício (por condução via estrutura ou por convecção através de equipamentos de água ou ar) e a bomba de calor, que liga os dois circuitos, permitindo as trocas de calor sazonais (Brandl, 2006).

The influence of ground water level on shallow foundation design is presented for the ultimate limit state of the bearing resistance, according to the formulation presented in annex D of EN 1997:2004. Probabilistic and deterministic methods were used and compared. Concerning probabilistic methods, the advanced first-order second-moment method (AFOSM) was applied and the results were validated by Monte Carlo simulations. For the deterministic calculation, the partial factors method recommended by the Eurocode and applied in most practical cases, was implemented. For the assumptions herein made the width B determined by the probabilistic method is always smaller than the one obtained deterministically.

The main purpose of the thesis is to show that it is viable the use of a correct effective stress framework to model the behaviour of unsaturated soils, with the development of an adequate effective stress model being an essential factor. One of the main advantages of this methodology is the separation between the solid skeleton mechanical constitutive models, which can be those developed for saturated soils, and the effect of the partial saturation on the behaviour of the soil, being only influenced by the effective stress model. The effective stress framework consists on the solid skeleton mechanical, the soil-water retention and the effective stress models. An isotropic effective stress model is proposed based on the main characteristics of the effective stress evolution in cubic spheres arrangements, incorporating hysteretic behaviour between drying and wetting paths and the dependency of specific volume and temperature, and being a function of the degree of saturation. A soil-water retention model is also proposed incorporating the hysteretic behaviour existent in drying and wetting paths, its dependency of specific volume and the incorporation of unsaturated states with zero suction. A rate-dependent (viscoplastic) and a rate-independent (elastoplastic) mechanical constitutive models, formulated with the subloading concept and the same hardening laws, was presented. The mechanical models can reproduce the cyclic, anisotropic and structured behaviour. Additionally, it is presented their expansion to nonisothermal conditions and the convergence of the response of the viscoplastic model to the elastoplastic model, when dealing with rate-independent soil behaviour (the elastoplastic model being more efficient). A generalised mixed stress-strain control for both viscoplastic and elastoplastic models in non-isothermal conditions is given. The effective stress framework constituted by the proposed mathematical models can reproduce with success diverse and complex unsaturated laboratory tests, reproducing the main aspects of the unsaturated soils behaviour. It is concluded that with an adequate effective stress model, it is not necessary to modify the mechanical constitutive models, previously formulated for saturated soils, introducing dependence of several model parameters on suction, degree of saturation or other similar variables. Also, it is shown that with an adequate evolutionary algorithm, the number of parameters is no longer a relevant issue restraining the use of these complex constitutive models. A newversion of the Differential Evolution method is developed to calibrate constitutive models for the laboratory tests.

A state-of-the-art revision of immersed tunnels is done. The selected case-study for this thesis, an immersed tunnel for crossing Tagus River between Algés and Trafaria, is presented. Next, cases of earthquake-induced liquefaction and its associated mechanism are discussed. The most relevant constitutive models for the numerical simulation of the response of soils under cyclic loading are described, including the Manzari-Dafalias model. Subsequently, Tagus River sand is physically characterized and six monotonic drained triaxial tests are analysed, with the goal of characterizing the stress-strain behaviour of the sand and obtain its parameters. Five cyclic undrained torsional tests are also analysed with the goal of characterizing cyclic behaviour of the sand. Then, the calibration framework for the Manzari-Dafalias model is presented, combining results of laboratory tests with numerical sensitivity studies. A parameter sensitivity analysis is carried out to understand the relevance of some chosen model parameters, by using an OpenSees constitutive driver, both through numerical simulation of monotonic drained triaxial tests and of cyclic undrained torsional tests. Some model parameters are calibrated directly from triaxial testing. The remaining parameters are calibrated through numerical simulation and curve fitting of the model to the laboratory results. A new constitutive driver is implemented in MATLAB to clarify some of the Manzari-Dafalias model issues, namely in the liquefaction phase. Finally, multiple liquefaction mitigation measures, and their application in immersed tunnels, are described. Laboratory testing of a mitigation measure, specifically injection of a duromeric expansive polyurethane resin, commercially available, is accomplished. The physical characteristics of both the resin and of the sand-resin mixture are presented. A series of tests, namely high frequency ultrasonic pulse tests, uniaxial compression and tensile tests, and triaxial compression tests, are performed. The modulus of elasticity, the Poisson

Os objectivos deste projecto inserem-se no âmbito dos trabalhos desenvolvidos no Núcleo deFundações, Taludes e Obras de Suporte, do Departamento de Geotecnia do LaboratórioNacional de Engenharia Civil (LNEC/DG/NFTOS), e pretende realizar-se um estudo docomportamento das obras ancoradas, respondendo a solicitações do mercado exterior e poroutro lado analisar um tipo de obras que são uma prática constante e cujo comportamento amédio e longo prazo não se encontra devidamente analisado na literatura da especialidade.Esta dissertação objectiva ser um contributo para o dimensionamento, construção e ensaios deancoragens pré-esforçadas em terreno, isto é, pretende-se com este trabalho elaborar umdocumento de apoio bibliográfico para a indústria nacional associada à construção deancoragens. Pretende ainda permitir compatibilizar e estabelecer procedimentos de projecto econstrutivos em conformidade com as normas e com a finalidade de garantir a qualidadedesejável na construção de ancoragens, para garantir a vida útil prevista das obras deEngenharia. De acordo com o mencionado desenvolvem-se e apresentam-se matériasconsideradas importantes para atingir essas finalidades.Analisa-se a bibliografia relativa à documentação normativa e regulamentar, considerada maisrelevante, com um levantamento generalizado desses elementos, onde é avaliada a relevânciarelativa de cada um dos aspectos tratados, comparando-se e confrontando-se os diferentesdocumentos em assuntos comuns. Abordam-se questões associadas ao dimensionamento ecom os factores de segurança de ancoragens. Para tal considera-se a bibliografia relevante eem vigor.Havendo a preocupação em garantir a durabilidade das obras e sendo a integridade física dasancoragens uma preocupação na garantia da sua vida útil aborda-se a problemática dacorrosão, dos diversos tipos de corrosão e das classes de protecção das ancoragens contra acorrosão. Indicam-se ainda métodos expeditos para avaliar a carga corrosiva do meio e seuefeito na selecção do tipo de protecção a considerar para as ancoragens.Para optimizar os trabalhos associados às ancoragens, desenvolvidos no LNEC, e odesenvolvimento de novas metodologias relacionadas com obras de suporte com ancoragensdefinitivas pretende-se preencher algumas lacunas, nomeadamente no que se refere àviabilização da homologação de tecnologias de ancoragens com a participação do LNEC.Estando disponíveis no mercado diversos sistemas de ancoragens e havendo a possibilidadede recorrer a diversas tecnologias apresenta-se algumas referências nessa área e aborda-sediversos aspectos construtivos e tecnológicos. Sendo corrente o compromisso entre aqualidade final da obra, a mão-de-obra e outros factores construtivos, analisa-se a temática daqualidade das ancoragens e das estruturas ancoradas. Apresenta-se uma referência aos diferentes tipos de ensaios de carga, a realizar nasancoragens, bem como o número e tipo de controlo que a bibliografia recomenda para a suarealização. Indicam-se os critérios de análise e respectivas metodologias.Sendo o factor de fluência, ks, um parâmetro condicionante do comportamento dos solos, amédio e longo prazo, pretende-se calcular o seu valor a partir dos ensaios de carga realizadosnas ancoragens. Face aos problemas associados ao cálculo de ks a partir dos ensaios de carga,desenvolveu-se um modelo capaz de simular todos os aspectos de carga e descarga,integrados no ensaio, incluindo os patamares de fluência, e realizam-se análises com afinalidade de esclarecer esses problemas, propondo-se procedimentos para optimizar asestimativas correspondentes.Consideram-se os ensaios de carga primordiais para a caracterização mecânica das ancoragense para avaliar o comportamento da estrutura de suporte ancorada. Apresenta-se um sistema deensaios automático (SEA) para o controlo dos ensaios de carga de ancoragens in situ, que sedesenvolveu no âmbito deste trabalho. Relativamente a aplicações futuras desse sistema,SEA, apresenta-se a metodologia utilizada pelo LNEC no controlo das blocagens e no cálculoda tracção residual ou efectiva de blocagem.

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The growing concerns about the climate change and the negative environmental impacts of heating andcooling systems operated by fossil fuels, have led the technical and the scientific communities to find out more environmentally and sustainable energy alternatives, such is the case of shallow geothermal sources. Shallow geothermal systems use the ground as a heat reservoir, transferring thermal energy from the ground to a building, or vice-versa, with the help of a heat pump, to provide warmth in winter and cooling in summer. A proper evaluation of the thermal properties of the soil is essential in their design process and for a sustainable system. Thermal conductivity is the most important parameter for this evaluation. Thermal conductivity can be estimated or measured by several methods, namely by means of empirical correlations, and experimentally, either in situ, by means of the well-known Thermal Response Tests (TRT), or in the laboratory, under steady state or transient conditions. This work presents a series of thermal conductivity measurements on dry sand samples obtained by means of a high accuracy system with reference TPSYS02 Hukseflux equipped with Non-Steady-State Probes (NSSP) (TP02 or TP08). The system was acquired in the aim of an FCT research project. The work includes the completion of a guide to procedures to the use of the thermal measurement system. Details of its calibration as well as results from tests in soil samples are also presented.

This document describes the work developed in the short term scientific mission, STSM, of the COST TU1202, entitled Implementation of subloading constitutive models in material point methods, hosted by Dr. Phil Vardon, in the Technical University of Delft, TU Delft. A dynamic version of the material point method, MPM, in two-dimension was programmed, with the computer language Fortran. An elastoplastic subloading soil model with anisotropy, cyclic behaviour and structure was implemented in the program. The constitutive model was integrated using an explicit algorithm.

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Este relatório tem como objectivo a apresentação e análise dos resultados obtidos nas campanhas de observação e nas visitas de inspecção realizadas até ao mês de Janeiro de 2007, inclusive. Considera-se, assim, que com a apresentação deste relatório ficam concluídos os planos de trabalhos relativos aos períodos de observação de 2005 e 2006.

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Esta publicação objectiva ser um contributo para o dimensionamento de ancoragenspré-esforçadas em terreno. Pretende, também, permitir compatibilizar e estabelecerprocedimentos de verificação do dimensionamento de projecto de sistemas ancorados, emconformidade com as normas e com a finalidade de garantir a vida útil prevista das obras desistemas ancorados.Analisa-se a bibliografia relativa à documentação normativa e regulamentar, mais relevante.Avalia-se a importância relativa de cada um dos aspectos tratados, considerando-se abibliografia relevante em vigor, comparando-se os diferentes documentos e abordandoaspectos associados ao dimensionamento e aos coeficientes de segurança de ancoragens.O conceito associado ao sistema constituído por uma estrutura ancorada visa gerar umamassa de solo internamente estável para um nível de carga de serviço adequado. Odimensionamento das obras de suporte realiza-se, na maioria dos casos, pela análise decondições correspondentes a estados limites últimos, aplicando um determinado valor para ocoeficiente de segurança, isto é, para situações correspondentes a equilíbrio limite. No casode obras de suporte ancoradas, há que considerar também os riscos associados às ancoragenspropriamente ditas.Desta forma, na maioria dos casos, impõem-se limites de deslocamentos, do terreno e daestrutura, face às limitações de esforços a que se podem submeter os suportes e as ancoragensnas diversas fases da vida da obra.Por outro lado, no dimensionamento da ancoragem como elemento estrutural, devemconsiderar-se as diversas exigências de cada uma das partes que a constitui, quer ao nível dedesempenho, quer ao nível das acções consideradas.

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