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The purpose of this thesis is to analyse the behaviour of single piles under axial loading, as far as settlement and load transfer mechanisms are concerned. It includes a literary review of two elastic theorybased methods, the Poulos and Davis method and the Randolph and Wroth method, as well as axisymmetric elastic modelling using the finite elementbased program Plaxis. The results given by each method are organized in dimensionless charts of loadsettlement ratio and proportion of load transferred to the pile base in terms of the pile slenderness ratio and the soil inhomogeneity and compared amongst each other. This thesis also includes two comparison studies which involve axisymmetric elastoplastic modelling in Plaxis, considering the MohrCoulomb failure criterion. The first one is a comparison with two previous finite element simulations subject to very similar conditions: a GEFdyn 3D simulation and a CESARLCPC 2D axisymmetric simulation. It showed that in the simulation performed by Plaxis the value of load transferred to the pile base was lower than the others, although the total loadsettlement curve was very similar in all three cases. The second one is a case study of the simulation of a static load test performed on a test pile. It includes the geological description of the site and the justification of the choice of parameters introduced in the model. Although limited information is available regarding the geological and geotechnical conditions of the site, the overall results were quite satisfactory.
Behaviour of Single Piles under Axial Loading Analysis of Settlement and Load Distribution Joana Gonçalves Sumares Betencourt Ribeiro Thesis to obtain the Master of Science Degree in Civil Engineering Examination Committee Chairperson: Prof. José Manuel Matos Noronha da Câmara Supervisor: Prof. Jaime Alberto dos Santos Member of the Committee: Prof. Peter John Bourne-Webb May 2013 To my parents Aos meus pais May the God of hope fill you with all joy and peace in believing, so that by the power of the Holy Spirit you may abound in hope. Romans 15:13 Que o Deus da esperança vos mantenha felizes e cheios da paz que nasce pela fé, para que abundeis na esperança pelo poder do Espírito Santo. Romanos 15:13 ABSTRACT The purpose of this thesis is to analyse the behaviour of single piles under axial loading, as far as settlement and load transfer mechanisms are concerned. It includes a literary review of two elastic theory-based methods, the Poulos and Davis method and the Randolph and Wroth method, as well as axisymmetric elastic modelling using the finite element-based program Plaxis. The results given by each method are organized in dimensionless charts of load- settlement ratio and proportion of load transferred to the pile base in terms of the pile slenderness ratio and the soil inhomogeneity and compared amongst each other. This thesis also includes two comparison studies which involve axisymmetric elastoplastic modelling in Plaxis, considering the Mohr-Coulomb failure criterion. The first one is a comparison with two previous finite element simulations subject to very similar conditions: a GEFdyn 3D simulation and a CESAR- LCPC 2D axisymmetric simulation. It showed that in the simulation performed by Plaxis the value of load transferred to the pile base was lower than the others, although the total load-settlement curve was very similar in all three cases. The second one is a case study of the simulation of a static load test performed on a test pile. It includes the geological description of the site and the justification of the choice of parameters introduced in the model. Although limited information is available regarding the geological and geotechnical conditions of the site, the overall results were quite satisfactory. Key words: axially loaded pile, numerical modelling, soil-pile interaction, Poulos and Davis, Randolph and Wroth RESUMO O objectivo desta tese é analisar o comportamento de estacas isoladas sob carga axial, em termos de assentamento e mecanismos de transferência de carga. Inclui uma revisão literária de dois métodos baseados na teoria da elasticidade, o método de Poulos e Davis e o método de Randolph e Wroth, bem como a modelação elástica em estado axissimétrico utilizando o programa de elementos finitos Plaxis. Os resultados obtidos a partir destes métodos estão organizados em ábacos da relação carga-assentamento e carga da ponta-carga total em termos do factor de esbelteza da estaca e da variação de rigidez do solo, e são comparados entre si. Esta tese inclui também dois estudos de comparação que incluem modelação elastoplástica em estado axissimétrico utilizando Plaxis, considerando o critério de cedência de Mohr-Coulomb. O primeiro estudo trata-se de uma comparação com duas simulações numéricas realizadas anteriormente em condições idênticas: uma simulação 3D utilizando GEDdyn e uma simulação em estado axissimétrico utilizando CESAR-LCPC. Este estudo mostra que na simulação em Plaxis o valor da carga transferida para a base era inferior ao das outras simulações, apesar de a curva de carga no topo-assentamento no topo ser semelhante nos três casos. O segundo é um caso de estudo que consiste na simulação de um ensaio de carga estático executado numa estaca experimental. Inclui uma descrição geológica do local e a justificação da escolha de parâmetros introduzidos no modelo. Apesar da pouca informação disponível relativa às condições geológicas e geotécnicas do local, os resultados foram bastante satisfatórios. Palavras-chave: estacas sob carga axial, modelação numérica, interacção solo-estaca, Poulos e Davis, Randolph e Wroth [...]... methods of analysis of single piles under axial loading; 2) To compare solutions given by finite element 2D elastic modelling of piles with the results of the elastic theory-based methods; 3) To perform finite element 2D elastoplastic modelling of single piles under axial loading, validating its results with former numerical simulations and finally analysing a real case study This thesis consists of six... elastic theory-based methods that analyse the behaviour of single piles under axial loading: the Poulos and Davis method and the Randolph and Wroth method This review focuses in settlement and load transfer mechanisms Results are organizes in dimensionless charts Chapter 3 presents the results of 2D axisymmetric elastic modelling of single piles under axial loading, also organized in dimensionless charts... single piles under axial loading is therefore an essential basis for deep foundation design It is very important that the physical interaction between pile and soil is carefully studied The settlement analysis is also fundamental, for the maximum allowable settlement of a foundation is often the most important criterion in its design Thus, it should be estimated accurately The behaviour of single piles. .. shaft d: diameter of the pile shaft db: diameter of the pile base E: Young’s modulus of the soil Einterface: Young’s modulus of the soil-pile interface EL/2: Young’s modulus of the soil at the middle of the pile EL: Young’s modulus of the soil at the pile base Ep: Young’s modulus of the pile Eoed: Young’s modulus of the soil for oedometer loading conditions Eoed, interface: Young’s modulus of the soil-pile... Poulos and Davis estimation 84 Table 5.13: Randolph and Wroth (compressible piles) estimation 84 vii viii SYMBOLS Latin alphabet A: area of the cross section of the pile Ab: area of the pile base As: area of the pile shaft CK: correction factor for pile compressibility Cν: correction factor for Poisson’s ratio of soil c: cohesion of the soil cu: undrained strength of the soil ̅... value of K L Figure 2.5: Correction factor for the finite depth of the layer on a rigid base, Rh, in terms of the relation between the total depth of the soil layer and the length of the pile, h/L, and of the pile slenderness ratio, L/d (Poulos & Davis, 1980), p.89 9 ν Figure 2.6: Correction factor for the Poisson’s ratio of the soil, Rν, in terms of the soil’s Poisson’s coefficient, ν, and of the... h, in terms of the relation between the total depth of the soil layer and the length of the pile, h/L, and of the pile slenderness ratio, L/d (Poulos & Davis, 1980), p.89 9 Figure 2.6: Correction factor for the Poisson’s ratio of the soil, Rν, in terms of the soil’s Poisson’s coefficient, ν, and of the relation between the pile’s and the soil’s Young’s modulus, K (Poulos & Davis, 1980),... ratio, L/r0, the proportion of load transferred to the pile base, Pb/Pt, and the load settlement ratio, Pt/(wtr0GL) Figure 2.2: Pile under axial loading – relevant parameters 5 2.2 Poulos and Davis Method This method, firstly presented in (Poulos & Davis, 1968), allows a quick estimation of both the proportion of load which reaches the pile base and the total settlement of a pile in the conditions... interface for oedometer loading conditions G: shear modulus of the soil Ginterface: shear modulus of the soil-pile interface GL/2: shear modulus of the soil at the middle of the pile GL: shear modulus of the soil at the pile base h: total depth of the soil layer, i e distance between the soil surface and the rigid layer I: coefficient used in the calculation of the total settlement of the pile I0: settlement-influence... modulus of layer i hi: thickness of layer i n: number of layers/divisions of the soil This may be used when the soil is divided into different layers but the Young’s modulus does not vary much In those cases, the solution may be calculated with this new value of the Young’s modulus and is very close to the one provided by the finite element method (errors inferior to 15%), according to (Poulos & Davis,