Influences of friction fatigue effects of conductor-soil interface on penetration resistance of conductor of wellhead in deep water

The penetration resistance of deep-water conductor in clay is closely related to the friction fatigue at the conductor-soil interface. The shear stress at the conductor-soil interface decreases because of the friction fatigue caused by the installation of conductor. The penetration process of the conductor is simulated by using the arbitrary Lagrange-Euler method (ALE) in ABAQUS. The friction fatigue effects of the adhesive contact interface between the conductor and the soil is simulated by using the VUSDFLD and VFRIC subroutines. The influences of friction fatigue on penetration resistance of the conductor and the fundamental principles of reciprocation in homogeneous clay and heterogeneous clay are studied. The results show that the cohesion coefficient at the conductor-soil interface gradually decreases with the penetration and approaches the inverse of the soil sensitivity due to the friction fatigue effects, resulting in a reduction in the unit shaft resistance. The total penetration resistance of the conductor in homogeneous clay and heterogeneous clay decreases by 42.60% and 28.48%, respectively at the end of penetration. The reciprocation of the conductor increases the "cumulative shear displacement" of soil, which inflicts significant fatigue damage to the soil at the conductor-soil interface, and the penetration resistance of the conductor decreases, so that the "stuck" conduction can continue to penetrate into the design depth.