Effect of spatial variability of cone penetration resistance on probabilistic axial capacity of pile foundations

The Cone Penetration Test (CPT) is site-specific and it is one of the predominant tests in geotechnical investigations used for varied offshore and onshore facilities. The evaluation of axial load carrying capacity of pile is one such use. Due to their continual records, CPT-based methods are appropriate in the offshore environments. Uncertainties are prevailing in most of the engineered systems and implementation of spatial correlation in the probabilistic geotechnical studies possess a paramount importance to overcome the uncertainties. In the present study, the influence of spatial correlation in the CPT data towards the load carrying capacity of pile group in sandy soil is examined. The in-situ test approach involving the spatial correlation of the CPT data in the analytical formulations is established in the study. The inclusion of spatial correlation intervening the spatial averages of CPT data obtained along the soil profile for the pile length, qc,a and at its base, qc,s is studied. Variance reduction technique is utilized for developing the one-dimensional spatial correlation. The failure probability and its relationship with the factor of safety is illustrated based on the Rackwitz's first-order reliability method (FORM). The results of the analyses have shown that, the inclusion of spatial correlation imparts a significant effect on failure probability and which when ignored will result in an unsafe design. A test pile group is analyzed to exemplify the reliability assessment of axial pile load carrying capacity by considering the spatial correlation of CPT data. This approach can be utilized for the safer pile design practices within the probabilistic framework.