Probabilistic Evaluation of Penetration Resistances

Abstract

In the installation of an offshore gravity platform, proper anchoring of a skirt system into the seabed is important. The penetration of the skirt system is generally achieved by built-in ballasting system. Because of (1)inherent spatial randomness in soil resistance; (2)uncertainty in the exact location of the installed platform; (3)insufficient cone penetration test (CPT) values over platform base; and (4)calibration error in predicting skirt penetration resistance from CPT values, the average penetration resistance and the resultant unbalanced moment (in maintaining a horizontal platform position) at each depth of penetration cannot be predicted accurately. A probabilistic model is formulated which will predict the statistics of the penetration resistance and unbalanced moment for a given platform and site condition at any depth of skirt penetration. Such information will help in the design of the capacity of the ballast system. The probabilistic model is also extended to cover the case of sloping seabed.