Monte-Carlo simulations are conducted within a reliability-based framework to calibrate resistance factors for the ultimate limit state design of footings resting on clays improved with granular columns. Resistance factors are calibrated for different design scenarios to ensure target reliability levels. Results indicate that the required resistance factors are dependent on the ratio of dead to live load, clay sensitivity, area replacement ratio, and the target probability of failure. For practical designs, it is recommended that resistance factors in the range of 0.5 to 0.55 be used for sites with relatively low undrained shear strength variability. These resistance factors ensure designs with a probability of failure of 1%. For more stringent target probabilities of failure (p_f = 0.1%), the resistance factors should be decreased to about 0.4. For more variable sites, the resistance factors range from 0.38 to 0.55 (for p_f = 1%) and from 0.25 to 0.40 (for p_f = 0.1%).
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