Serviceability limit state CPT-based design for vertically loaded shallow footings on sand

In this study, reliability-based design of vertically-loaded shallow foundations on cohesionless soil at the serviceability limit state is addressed and related to cone penetration resistance. A special database of 30 large footings on 12 different sands is investigated in a statistical and probabilistic perspective to quantify the load-displacement-capacity response and derive a direct design method based on cone penetrometer testing (CPT). A reference load-displacement model is identified through a comparative assessment of fitting of model types to load test data. The uncertainties in the load-displacement model and in the model inputs are modeled probabilistically. The probability of exceedance of a target probability of occurrence of a pre-established allowable settlement is computed in the form of a reliability index through Monte Carlo simulation. A partial load factor is defined and calibrated based on simulation outputs. Analytical expressions for the load factor as a function of the ratio of allowable settlement to footing dimensions are derived using least squares regression. The final design format allows simple and practical utilization on the part of the engineer while ensuring the minimization of excess conservatism.

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