A Probabilistic Approach for Mud Mat Stability Analysis

Subsea structures are typically supported on mud mat type foundation systems. Traditional approaches for mud mat foundation stability analysis consider calculating the factors of safety using the classical methods given in API RP 2A or the more recent API RP 2GEO. Due to the inherent uncertainties in soil properties and subsea structure forces, conservative factors are generally required, consequently resulting in over-designed mud mat systems. In the present study, a probabilistic response analysis of a mud mat type foundation system is conducted. The effects of uncertainties in the soil properties are evaluated and quantified. Specifically, DNV RP C207 is utilized for the statistical representation of the soil. An approximate analytical approach is proposed to solve for the response probability density function (PDF). Further, the probability of failure is derived directly from the response PDF. A numerical example is presented to illustrate the simplicity of the proposed approach and the results are compared to simulations performed using the Monte Carlo method. In addition, the importance of uncertainty modeling and stochastic-based analysis approaches in the context of subsea systems are discussed.