Probabilistic equivalent linear soil spring stiffness analysis for gravity platforms: Illustrative example

The companion paper [1] suggests a procedure to perform equivalent linear soil spring stiffness analysis for gravity platforms founded on clay and loaded under undrained conditions. This paper provides an example to illustrate the suggested procedure. The CONDEEP SP4-10-24 platform concept proposed for the Troll field was used for the example. Plastic Drammen clay was chosen as the foundation soil to a depth of 150 m. Wave loads on the platform were estimated assuming a 70 yr platform life, plus an 18 hr storm build-up, plus a 6 hr storm with a return period of 100 yrs. The constitutive model for the soil was calculated for the 6 hr rare event in the load history, assuming that the rare even occurs at the end of the load history. The coefficients of variation of the equivalent soil spring stiffnesses (horizontal and rotational) were found to be around 0.50.