Abstract This work aims to analyze the behavior of a new post-grouted micropile setup developed in tropical soil. Its main innovation is the use of high mechanical resistance steel pipes (N80 class) for drilling and as a structural component of the micropiles. The pipes have special manchette valves uniformly spaced to allow neat cement grout injection into the soil. Two instrumented micropiles with 0.3 m diameter (after injection) and lengths of 19.4 m and 21 m were installed at Experimental Site III of the University of Campinas (Unicamp). The geological profile of this site presents a sandy clay surface layer (porous and collapsible) followed by a layer of sandy silt (diabase residual soil). The piles were subjected to compressive slow maintained loading tests and were instrumented along their depth with strain gages. No geotechnical failure was observed during the load test. The maximum load achieved by the MC1 and MC2 micropiles were 2.210 kN and 2.470 kN, respectively. The load test data were extrapolated to estimate the ultimate geotechnical pile capacity. The extrapolated geotechnical failure load was above 2.500 kN for both micropiles and similar to those estimated by the Federal Highway Administration FHWA (2005) load capacity method. It was verified that (1) the pile material undergoes creep under stress above 25 MPa on the transversal section of the pile and (2) the debonding effect during the loading process. The micropiles showed higher values of skin friction compared with other piles installed in the same geological-geotechnical context (tropical soil).

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 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.

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.

En la práctica de la ingeniería geotécnica es común el empleo de fundaciones por pilas cargadas transversalmente en la parte superior. Frecuentemente este tipo de fundación es ejecutada en suelos de alta porosidad y colapsables, comunes en varias regiones de Brasil. Debido a la poca información disponible en la literatura, se realizaron dos pruebas de carga con cargamento transversal en una pila (diám. 0,8 m; prof. 9,0m; diám. base 1,60m). Se realizó una prueba de carga estando el suelo en su condición de humedad natural y otra después de la previa inundación. Fueron obtenidas las curvas carga x desplazamiento horizontal y los coeficientes de reacción horizontal. Los resultados permitieron verificar la aplicabilidad de fórmulas teóricas de previsión de comportamiento, así como proponer parámetros a ser utilizados para el suelo. Previo a la realización de las pruebas de carga fueron realizados ensayos de laboratorio y campo para la investigación del subsuelo.

In geotechnical engineering, the use of caisson foundations transversally loaded at the top is common. This type of foundation is frequently used on high-porosity and collapsible soils, which are common in many regions in Brazil. Because of the limited information available in the literature, two loading tests were performed with transversal loading in a caisson built at full scale (0.8 m diameter, 9.0 m depth, 1.6 m base diameter). A load test was performed with the soil in its natural humidity condition, and another load test was performed after the previous soil flooding. Load vs horizontal displacement curves and the horizontal direction coefficient of the soil were obtained. The results permitted the verification of the applicability of behavior-predicting theoretical formulae in addition to the proposal of parameters for use on the studied soil. Before executing the load tests, laboratory and in-situ tests were performed to investigate the local subsoil.

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.