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<p class="MsoNormal" style="text-align: justify; line-height: 200%;">Axial bearing capacity (ABC) of piles is usually determined by static load test (SLT). However, conducting SLT is costly and time-consuming. High strain dynamic pile testing (HSDPT) which is provided by pile driving analyzer (PDA) is a more recent approach for predicting the ABC of piles. In comparison to SLT, PDA test is quick and economical. Implementing feed forward back-propagation artificial neural network (ANN) for solving geotechnical problems has recently gained attention mainly due to its ability in finding complex nonlinear relationships among different parameters. In this study, an ANN-based predictive model for estimating ABC of piles and its distribution is proposed. For network construction purpose, 36 PDA tests were performed on various concrete piles in different project sites. The PDA results, pile geometrical characteristics as well as soil investigation data were used for training the ANN models. Findings indicate the feasibility of ANN in predicting ultimate, shaft and tip bearing resistances of piles. The coefficients of determination, R², equal to 0.941, 0.936, and 0.951 for testing data reveal that the shaft, tip and ultimate bearing capacities of piles predicted by ANN-based model are in close agreement with those of HSDPT. By using sensitivity analysis, it was found that the length and area of the piles are dominant factors in the proposed predictive model.</p><p class="MsoNormal" style="text-align: justify; line-height: 200%;"> </p><p class="MsoNormal" style="text-align: justify; line-height: 200%;"><strong>Resumen</strong></p><p class="MsoNormal" style="text-align: justify; line-height: 200%;">La Capacidad Axial de Soporte (ABC, en inglés) de un pilote de construcción se determina usualmente a través de una Prueba de Carga Estática (SLT, inglés). Sin embargo, estas pruebas son costosas y demandan tiempo. La evaluación de las Dinámicas de Alto Esfuerzo de Pilotes (HSDPT, inglés), que la provee el programa de Análisis de Excavación (PDA, inglés), es una forma de aproximación más reciente para preveer la Capacidad Axial de Soporte. En comparación con la Prueba de Cargas Estática, la evaluación PDA es rápida y económica. La implementación de Redes Neuronales Arficiales (ANN, en inglés) que permita resolver problemas geotécnicos ha ganado atención recientemente debido a su posibilidad de hallar relaciones no lineales entre los diferentes parámetros. En este estudio se propone un modelo predictivo ANN para estimar la Capacidad Axial de Soporte de pilotes y su distribución. Para fines de una red de construcción se realizaron 36 pruebas PDA en pilotes de diferentes proyectos. Los resultados de los Análisis de Excavación, las características geométricas de los pilotes, al igual que los datos de investigación del suelo se utilizaron para probar los modelos ANN. Los resultados indican la viabilidad del modelo ANN en predecir la resistencia de los pilotes. Los coeficientes de correlación, R², que alcanzaron 0.941, 09.36 y 0.951 para la evaluación de los datos, revelan que la capacidad del pilotaje en el último rodamiento, en el cojinete del eje y en la punta que se predijeron con el modelo ANN concuerda con las establecidas a través del HSDPT. A través del análisis de respuesta se determinó que la longitud y el área de los pilotes son factores dominantes en el modelo predictivo propuesto.</p>

The effect of weathering processes in decreasing the shear strength of clay shale had been done in this study. The drying process of clay shale with sunlight in the laboratory up to 80 days had been conducted to create the conditions of weathered sample. The peak and residual shear strength parameters of unsaturated and saturated clay shale were obtained from triaxial laboratory test, and all samples were tested on each 8 days of weathering process. Decrease of shear strength in peak and residual condition was obtained during 80 days of the drying process. The residual shear strength parameters were distinguished between residual shear strength without stress release and with stress release of confining pressure. The results up to 80 days of unsaturated clay shale showed that the cohesion at peak stress conditions reduced to 30 % based on initial shear strength before the occurrence weathering, while the internal angle friction reduced to 64 %. Residual cohesion without and with stress release reduced to 4 % and 1 %, respectively while residual internal angle friction without and with stress release reduced to 15 % and 5 %. Similar situation also occurs for the saturated clay shale samples.

The purpose of this research is to determine the capability of (and the factors which affect the performance of) an enlarged base pier in resisting uplift capacity. Experiments were conducted in the reinforced bin box of an enlarged base pier with a shaft diameter ranging from 30 to 50 mm, base diameters between 75 and 150 mm and base angles of α = 30°, α = 45°and α = 60°. Tests were conducted in both loose and dense sand packing. A failure mechanism was studied in a glass box for loose and dense sand packing. A dry sand with a unit weight of γ d = 14.80 kN/m 3 and γ d = 17. 0 kN/m 3 was achieved for loose and dense packing, respectively. Increasing the bell angle and shaft diameter would result in a decrease of the net uplift capacity and failure displacement. This is due to the reduction in the amount of the sand column above the bell that resists the uplift of the pile. Failure displacements at a constant base diameter generally increased considerably with the increase of the embedment ratio but decreased with the increment of the sand density. It is thus apparent that the shaft diameter, bell diameter and bell angle are geometric factors which, together with the embedment ratio and the sand density, should be taken into account in the design of enlarged base piers.

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