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

In this paper, an immersed tunnel case-study, corresponding to a third Tagus river crossing,supported on liquefiable alluvial sands, is presented. Laboratory testing, namely monotonicdrained triaxial tests and cyclic undrained torsional tests, is described. Moreover, a constitutivemodel, as well as the numerical work, essential to its calibration and to identify its most relevantparameters, are presented. Model parameters, their respective reference values and testsperformed to determine directly most of the parameters, are introduced. A parameter sensitivityanalysis, conducted through numerical simulation of triaxial monotonic drained tests, is defined.Furthermore, a parameter sensitivity analysis through numerical simulation of cyclic undrainedtorsional tests, implemented both for the pre-liquefaction and liquefaction phases, is described.Finally, some parameters are determined by fitting the model to the laboratory results.

The complex nature of soil behaviour must be modelled with advancedconstitutive models. However, some difficulties can be highlighted that hinder the use and the development of advanced constitutive soil models in geotechnical research andpractice: the objective evaluation of the performance of model variants, the objectivecomparison between different models, the information on the effect of individualparameters (material model constants and initial values of internal variables) on themodel

In this paper, the numerical work that has been done to calibrate the Manzari-Dafalias model and to identify its more relevant parameters is presented. The model parameters, their respective reference values and the tests that were performed to determine most of the parameters are introduced. A parameter sensitivity analysis through numerical simulation of a triaxial monotonic drained test, using an OpenSees model with a single 1x1x1 m3 SSPbrickUP 3D element, is described and the results analyzed. The sensitivity analysis is conducted for each parameter individually, for several pairs of physically related parameters and of the most relevant ones. It is considered the final influence upon the peak values of the shear strain, shear stress ratio and dilatancy and upon the critical state volumetric strain.Furthermore, a parameter sensitivity analysis through numerical simulation of a cyclic undrained torsional test is implemented, both for the pre-liquefaction and liquefaction phases. In the former, the variation of some response parameters (namely the damping ratio, the shear modulus, the shear stress amplitude, the average shear stress, the shear strain amplitude and the average p) with the model parameters is evaluated for three different cycles.

This paper presents a thermo-viscoplastic subloading soil model with a mobile centre of homothety. The model is formulated to describe the influ-ence of non-isothermal conditions on the stress-strain-time behaviour of soils and is restricted to isotropic stress and strain conditions. Numerical simula-tions of three isotropic drained heating tests at constant isotropic effective stress for different overconsolidation ratios were performed. The model was able to accurately reproduce the experimental results.

This paper illustrates the capability of a new viscoplastic subloading model to reproduce the strain rate change effects. The viscoplastic subloading model used is based on the subloading surface concept with a mobile centre of homothety, enabling the occurrence of viscoplastic strains inside the yield surface. An undrained triaxial compression test performed on a normal consolidated reconstituted London Clay is modelled. The results show that this model is able to reproduce the strain rate change effects

This paper presents a viscoplastic overstress soil model that incorporates thesubloading surface concept with a moving centre of homothety. The model is formulated to represent the soil rate dependent behaviour under cyclic loading and incorporates both initial and induced anisotropy. The model was implemented into the explicit finite difference code 11 FLAC. The model was able to reproduce accurately the stress-strain response from cyclic undrained triaxial creep tests performed on a stiff clay from the Lisbon region (Formação de Benfica).

The complex nature of soil behaviour can only be modelled by advanced constitutive models. This type of models has the disadvantage of requiring a great number of parameters (material model constants and internal variables initial values) that must be defined. The application of Genetic Algorithms, GAs, appears to be a useful technique to solve this type of problem. Previous applications of GAs to the determination of soilmodels

Crestuma-Lever dam, completed in 1985, is located in Douro River. A large design flood of 26,000 m3/s involves 8 gated spillway bays with stilling basins directly founded on the alluvial river bed. Regular river bed surveillance downstream of the spillway evidenced unexpected progressive erosion of riprap.

Odelouca dam is an embankment dam, with 76 m height, recently constructedin the south of Portugal. It is zoned with a core consisting of colluvial and residual schistsoil, and with soil-rockfill mixtures making up the shells (weathered schist with a significant fraction of coarse sized particles). This paper presents a numerical analysis of Odelouca dam construction. In this analysis the explicit finite difference program FLAC is used. An unconventional elastoplastic soil model, a Subloading Surface type model, implemented into the program, is used to model the embankment materials. The main results are compared with those obtained with the Modified Cam Clay Model. The model

For engineering applications, the complex behaviour of hard soils / soft rocks can be modelled using advanced constitutive models, although they require a great number of parameters. The application of Genetic Algorithms with a local search technique has proven to be a useful tool to be used in their determination. A constitutive model for hard soil / soft rocks was used to fit the experimental results measured in tests performed in marl specimen. This model was implemented in the explicit finite difference code FLAC and its calibration was done using a Genetic Algorithm with Hill Climbing procedure implemented in MATLAB. The use of the two programs with complete distinct objectives (MATLAB to the fitting process and FLAC to the numerical calculations) provides great flexibility to the implementation of any constitutive model to reproduce the results from experimental tests.

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.

N/A

N/A

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.

N/A

N/A

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.

N/A

N/A

N/A

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.

N/A

N/A

N/A

N/A

N/A

N/A

N/A

Procedimentos recomendados pelo LNEC para a observação da integridade das cabeças das ancoragens das vigas ancoradas nos taludes subjacentes à PS3

N/A

O sistema de ensaio é composto por um conjunto de sete sensores inteligentes, ligados a uma unidade coletora de dados, através de uma rede de comunicação de dados do tipo digital, uma fonte de alimentação (para alimentação de todo o sistema de medição), uma consola portátil, dotada com uma bateria recarregável e respetivo carregador de bateria, um conjunto de cabos terminados com fichas, para estabelecimento do meio físico de comunicação e transporte da alimentação aos sensores inteligentes