Abstract The use of deep foundations is a common practice in geotechnical civil engineering designs, in which the bearing capacity of these foundations occurs by side resistance, tip, or through the combination of both. In the case of caisson, the bearing capacity is often obtained by considering only the resistance of the lower end due to its bell-shaped geometry, neglecting the skin friction resistance of the shaft, which may represent an oversizing in some cases. In this context, this paper analyzed the behavior of nine caisson prototypes laid at 10 m, 15 m and 20 m deep. At each depth, three types of caissons were analyzed, with and without an expanded base, and a third type with deformable material at the top of the base. The axisymmetric numerical analyses were conducted by using the finite element method considering an isotropic medium. Thus, it was found that with increasing depth, the skin frictional resistance of the surrounding soil of shaft contributes significantly to the bearing capacity of the caisson suggesting that little load would reach the base of the caisson in situations that would negligible the side resistance of the shaft in the design phase. This may be an important consideration in foundation design using caisson, as it would reduce risks to human life, as well as reduce material consumption and the generation of carbon released into the atmosphere.

Resumo A análise numérica do comportamento de radiers estaqueados assentes em solo uniforme e de baixa capacidade de suporte tem se mostrado importante para subsidiar a concepção do projeto. A calibração do modelo numérico com uma prova de carga instrumentada permite que os resultados possam ser aplicados, dentro das condições estabelecidas, ao projeto de fundações para edificações de pequeno e médio porte assentes em solos com as mesmas propriedades mecânicas analisadas neste artigo. Nesse sentido, o artigo avalia modelos numéricos, que permitam estudar a influência de estaca curta executada por escavação acoplada ao radier. Os modelos também são avaliados a partir dos conceitos de radier estaqueado. A partir dos resultados obtidos, verifica-se que a carga suportada pela resistência lateral, significativa para o caso de estacas escavadas, é de 14% a 30% maior para radiers mais flexíveis ou com menores espessuras. A introdução de estacas nos radiers promove a redução de recalques e o aumento da rigidez do sistema, tendo seus efeitos ampliados para estacas com esbeltezes (L/d) mais elevadas.

Abstract Numerical analysis of the behavior of piled rafts seated on uniform soil with low bearing capacity has been important to support the project design. The calibration of the numerical model with instrumented load test allows usage of the results, in given conditions, in the foundation design of small and medium-sized buildings built on soils with the same mechanical properties analyzed in this paper. In this context, this paper evaluates numerical models, which allow to consider the influence of short bored piles connected to the raft. The models are also assessed using piled rafts concepts. From the results obtained, the load supported by the total shaft resistance is significant for the case of bored piles, and this load is from 14% to 30% higher in the case more flexible or thinner raft. Inserting piles in the rafts reduces settlement and increases overall stiffness. Such effects are amplified in piles with higher slenderness ratios (L/d).

resumo: Nos últimos anos, a engenharia tem aumentado significativamente o uso da modelagem numérica, principalmente aplicada em estudos de soluções e análise do comportamento da interação solo - estrutura e elemento de fundação. Nesse sentido, este trabalho analisa o comportamento de fundações de blocos constituídos por uma, duas, três e quatro estacas com 25 cm de diâmetro (d) e 5 m de comprimento (L) e com espaçamentos não usuais entre as estacas, igual a 5d em um modelo numérico de elemento finito tridimensional (MEF-3D). Os resultados das análises numéricas demonstraram uma contribuição média de 36% devido ao contato bloco-solo em relação à capacidade total do sistema. A geometria do bloco influencia a resposta em termos de capacidade de carga e rigidez do elemento de fundação. Estes resultados demonstram uma oportunidade de reavaliar os requisitos tradicionais de cálculo, com o objetivo de racionalizar o dimensionamento das fundações, melhorando assim a segurança do sistema estrutural.

abstract: In recent years, engineering has significantly increased the use of numerical modeling, mainly applied in studies of solutions and analysis of the behavior of the soil - structure and foundation element interaction. In this sense, this paper analyzes the behavior of blocks foundations made up of one, two, three and four piles with 25 cm in diameter (d) and 5 m in length (L) and with unusual spacing between the piles, equal to 5d in a three-dimensional finite element numerical model (MEF-3D). The results of the numerical analyzes demonstrated an average contribution of 36% due to the block-to-ground contact in relation to the total capacity of the system. The geometry of the block influences the response in terms of load capacity and stiffness of the foundation element. These results demonstrate an opportunity to reevaluate traditional calculation requirements, with the aim of rationalizing the design of foundations, thus improving the safety of the structural system.

Abstract The methodologies for designing pile foundations can be complex since the simultaneous interactions among the block, piles and surrounding soil should be taken into account. Therefore, in addition to the discussions on construction, instrumentation, testing and simulation of a defective pile, this paper discusses the practical issues arising from the observed numerical using three-dimensional finite elements and experimental studies. The main issues discussed in this paper refer to as the decrease in load capacity of bored instrumented piles when subjected to a structural defect. It was observed in the results that given the presence of the defect, the failure load of the system has decreased from 190 kN to 110 kN, i.e. around 40% reduction of the intact reference value. Using the data obtained by numerical analysis, laboratory test, and field application, it was possible that the results were satisfactory and reasonable, enhancing our understanding of this complex foundation system’s behavior, especially in the presence of a defective pile.

Abstract Geotechnical engineering has often been challenged by demands from technically and economically bold construction projects, such as that of tall buildings. The architectural requirements of these buildings have increased and concentrated the loads from structural systems without proportionally increasing plant area. New forms of using load capacity and settlement control have been assessed to optimize conventional designs. Thus, piled foundations started to allow for the contribution of block-soil contact, being conceptually named piled raft. In this sense, this study analyzed the contribution of contact in piled foundations composed of one, two, three and four instrumented bore piles 25 cm in diameter ( ϕ) and 5 m in length (L). Experimental results showed a 21% average contribution of block-soil in relation to the total piled foundation capacity. This result demonstrates the need to re-evaluate traditional calculation requirements, aiming at rationalizing the geotechnical design and improving the overall safety/stability of the system.

ABSTRACT Applying numerical modeling to geotechnical engineering problems has become a powerful tool to interpret the behavior of foundations and earthworks. However, not all numerical analyses follow the requirements for the model to be representative of the experimental condition. This work describes the steps required during modeling to determine the appropriate dimensions of the half-space and the respective boundary conditions, as well as the tests appropriate to perform this determination. On the other hand, the results of comparisons between the numerical and the experimental model for a piled raft are shown.

RESUMEN El uso de modelos numéricos viene siendo cada vez más difundido y utilizado por investigadores y profesionales en el campo geotécnico. Las herramientas numéricas cuentan con precisión y velocidad en los análisis de alta complejidad. Los modelos numéricos más comunes se basan en el método de los elementos de contorno, de las diferencias finitas y de los elementos finitos. Siendo imprescindible para la validación del modelo numérico, la realización de pruebas de comparación con resultados de la literatura, pruebas de convergencia y calibración con parámetros experimentales. El modelado numérico por elementos finitos es una herramienta que permite simular las condiciones reales, desde que sean respetadas las etapas para la implementación del modelo numérico.

Resumen La predicción de los asentamientos de pilotes es considerada una tarea compleja para los investigadores y profesionales de la ingeniería geotécnica, lo anterior, teniendo en cuenta la diversidad de métodos de previsión y la dificultad de emplear modelos de previsión que representen el comportamiento no lineal del suelo. De esta manera, en este trabajo se evalúan dos métodos de previsión no lineal del asentamiento de un pilote raíz instrumentado, de 23 m largo y 31 cm de diámetro, a través de una prueba de carga estática lenta (SML). El subsuelo del área de estudio está compuesto por arcilla limo-arenosa coluvial, laterítica y colapsable en el estrato superficial (6,5 m), seguido por un estrato de limo arcillo-arenoso (residual) hasta una profundidad de 20 m. Los resultados mostraron que los modelos de comportamiento no lineal concuerdan correctamente con los resultados experimentales. También se verificó que fueron necesarios pequeños desplazamientos de la parte superior del pilote (5,1 mm), para la saturación de la fricción lateral, y que la reacción de la punta presentó un aumento continuo hasta la etapa final del ensayo.

Abstract Prediction of pile settlement is considered as a highly complex task by geotechnical engineering researchers and professionals, owing to the diversity of prediction methods and also to the difficulty to use predictive models that represent the nonlinear behavior of the soil. In this sense, this work assesses two methods for nonlinear prediction of the settlement of a 23-m long, 31-cm diameter instrumented root pile tested via slow maintained load (SML) test. The local subsoil is composed of colluvional silty-sandy, lateritic clay with a collapsible surface layer (6.5 m), followed by silty clayey sandy soil (diabase residue) down to 20 m. The results showed that the models of nonlinear behavior were in appropriate agreement with the experimentally obtained results. It was also noted that, for small displacements of the top (5.1 mm), the tip load increased continuously from its reaction to the final stage of the test.

Analisa-se o comportamento de quatro estacas-raiz (ϕ=0,41m) executadas na cidade de Foz do Iguaçu/PR, as quais foram submetidas a provas de carga com carregamento lento. Os resultados foram confrontados com aqueles obtidos por meio de modelagem numérica tridimensional pelo método dos elementos finitos, o qual permite simular o comportamento elásto-plástico do solo. O subsolo local apresenta variada estratigrafia, composto por uma camada superficial de solo residual, seguida por alteração de rocha e rocha sã em poucos metros de profundidade. Os parâmetros geotécnicos do maciço foram determinados por meio de correlações obtidas a partir de ensaios de campo, estimando-se os valores de coesão, ângulo de atrito, módulo de deformabilidade e resistência à compressão uniaxial das diferentes camadas do subsolo. As provas de cargas foram interrompidas quando alcançaram 3000 kN, apresentando deslocamentos inferiores a 5mm na carga de trabalho (1500 kN). Verificou-se que as estacas trabalharam por atrito lateral com tensões médias da ordem de 70 kPa, para o trecho superficial (solo residual), e superiores a 150 kPa, nos trechos em alteração de rocha. Os parâmetros geotécnicos estimados forneceram valores que se adequaram perfeitamente às análises numéricas. Nesse sentido, pôde-se verificar, através das análises realizadas e pelo modelo de transferência de carga, que seus comprimentos poderiam ser reduzidos, possibilitando otimizar o projeto geotécnico.

The behaviours of four foundation pilings (ϕ=0.41 m) constructed in Foz do Iguaçu, Paraná (PR), Brazil and subjected to slow loading tests were analysed. The results were compared with results from three-dimensional numerical modelling using the finite element method, which facilitates simulation of the elasto-plastic behaviour of soil. The local subsoil comprises varied stratigraphies; it is composed of a residual soil surface layer followed by weathered rock and bedrock, which are a few meters deep. The massif geotechnical parameters were determined through correlations obtained from field tests, whereby the values for cohesion, angle of friction, modulus of deformability and uniaxial compressive strength in the different subsoil layers were estimated. The load tests were interrupted at 3000 kN and displaced by less than 5 mm in the working load (1500 kN). The pilings were subjected to lateral friction work with an average stress of approximately 70 kPa for the surface portion (residual soil) and greater than 150 kPa for the weathered rock portions. The estimated geotechnical parameters provided values that were an exact match with the numerical analyses. Thus, given the analyses and load transfer method, the piling lengths can be reduced, which will facilitate the optimisation of the geotechnical design.