Expanded Database Assessment of Design Methods for Spread Foundations under Axial Compression and Uplift Loading

Abstract

This paper compiles two expanded databases—NUS/SpreadFound/919 and NUS/RockFound/270—to evaluate the calculation methods of foundation capacity, where the number is the number of load tests collated. The mean (bias) and coefficient of variation (COV) (dispersion) of the model factor, defined as a ratio of measured-to-calculated capacity, are computed. With the statistics of a ratio of calculated-to-observed foundation settlement reported in literature, design methods for foundation capacity and settlement are classified according to their ability to match measured values. Such a statistical-based classification provides the designer with a sense of the accuracy of a capacity or settlement model. For the 298 case records in NUS/SpreadFound/919, the uncertainty exhibited by the load-movement curves over their full range of movements is captured by two parameters in a hyperbolic fitting of measured data. Copula analysis is adopted to evaluate the observed correlation structure between the hyperbolic parameters. Finally, the model statistics are applied to calibrate the resistance factors in load and resistance factor design of spread foundations at ultimate and serviceability limit states.