http://repositorio.lnec.pt:8080/jspui/handle/123456789/221 2026-04-04T21:10:28Z 2026-04-04T21:10:28Z Pereira, C. http://repositorio.lnec.pt:8080/jspui/handle/123456789/1016526 2023-10-10T13:58:52Z 2011-11-01T00:00:00Z

Estudo do modelo constitutivo BBM. Influência da sucção na resistência ao corte Pereira, C. In the present dissertation, a study of the Barcelona Basic Model, BBM, is realized. The mathematical formulation is presented and developed, referring the assumptions and simplification assumed in each step. A set of laboratory tests that enable the determination of the model parameters is suggested and some considerations are elaborated about the influence that some parameters have on the model and the range of values that they should adopt. It is adapted to the BBM and implemented in MATLAB programming language two explicit integration algorithms, without proceedings to the error control, to strain and stress tensor increments, respectively, together with suction increments. A third explicit integration algorithm with proceedings to the error control, more effective for the implementation in automatic calculation programs, is also adapted. The formulation of the CODE_BRIGHT program is presented, indicating the necessary simplifications to the modelling of geotechnical structures. Comparative analyses are made between CODE_BRIGHT program and the implemented drivers, in order to validate the explicit integration algorithms adapted to the BBM and illustrate the main phenomena of the unsaturated soils that the BBM is capable of modelling. Some limitations of the model are presented and discussed. Finally, some general considerations are made about the evolution of the volumetric and deviatoric strain with the occurrence of the collapse phenomenon and the influence that the suction decrease may have in the evolution of the shear strength.

2011-11-01T00:00:00Z Pereira, C. http://repositorio.lnec.pt:8080/jspui/handle/123456789/1016525 2023-10-10T13:58:44Z 2020-01-01T00:00:00Z

Formulation of an advanced effective stress based constitutive model for unsaturated soils Pereira, C. 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 new version of the Differential Evolution method is developed to calibrate constitutive models for the laboratory tests.

2020-01-01T00:00:00Z Miranda, L. http://repositorio.lnec.pt:8080/jspui/handle/123456789/1012732 2020-06-22T09:42:56Z 2011-11-23T00:00:00Z

Influência da variabilidade geotécnica na subsidência devida à escavação de túneis urbanos Miranda, L. Na presente tese descreve-se a geometria da subsidência devida à escavação de túneis. Apresentam-se expressões empíricas que se baseiam no volume unitário de subsidência e na distância ao plano de simetria do túnel dos pontos de inflexão da curva teórica de subsidência. Analisa-se, então, as soluções algébricas existentes para a estimativa do campo de deslocamentos, que consideram os efeitos da contracção pura do túnel e da sua ovalização. Descreve-se, ainda, a problemática da modelação numérica bidimensional e tridimensional, fazendo referência aos diversos métodos de simulação do faseamento construtivo. Para poder analisar a influência da variabilidade e correlação espacial das propriedades do terreno nas estimativas de assentamentos causados pela escavação de túneis tem de se recorrer à Teoria dos Campos Aleatórios e à caracterização estatística dos parâmetros geotécnicos. Apresentam-se no capítulo 3 valores das estimativas de medidas estatísticas bem como algumas metodologias de modelação numérica da variabilidade espacial, das quais se destaca a que se baseia na transformada rápida de Fourier espacial. Desenvolvem-se duas ferramentas computacionais para analisar os deslocamentos à superfície causados pela escavação de túneis. A primeira baseia-se no método de Monte Carlo e nas formulações analíticas apresentadas e é aplicada à análise estatística e caracterização de bacias de subsidência em terreno argiloso ligeiramente sobreconsolidado. A segunda baseia-se na geração de campos aleatórios correlacionados espacialmente e permite avaliar a influência da variabilidade espacial dos parâmetros do terreno na dispersão dos assentamentos superficiais. Com base nesta última, compara-se os resultados numéricos com resultados observacionais dum caso de obra.

2011-11-23T00:00:00Z Miranda, L. http://repositorio.lnec.pt:8080/jspui/handle/123456789/1012694 2020-06-22T09:42:48Z 2019-05-09T00:00:00Z

Liquefaction mitigation measures: prospective application to immersed tunnel foundations Miranda, L. 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’s ratio, the uniaxial compressive and tensile strengths, the triaxial compressive strength and the shear strength parameters, are determined. Two additional injection tests are executed to check densification of the sand between injection columns and its relative density is determined. Finally, the main conclusions are summarized and guidelines for future developments are established.

2019-05-09T00:00:00Z