管土界面摩擦疲劳效应对深水井口导管贯入阻力的影响

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

深水井口导管在黏土中的贯入阻力与导管土体界面产生的摩擦疲劳密切相关。在导管安装过程中,管土界面会产生摩擦疲劳,使得导管–黏土界面处的侧摩阻力降低。采用ABAQUS软件中任意拉格朗日欧拉法(ALE)模拟导管的贯入过程,并通过子程序VUSDFLD和VFRIC来模拟导管土体黏性接触面的摩擦疲劳效应,研究了在均质黏土和非均质黏土中,摩擦疲劳对导管贯入阻力的影响,以及循环划井眼解卡的基本原理。研究结果表明:由于摩擦疲劳的影响,管土界面之间的黏聚力系数随贯入位移逐渐降低并趋近于土体的灵敏度倒数,从而导致单位侧摩阻力降低,在贯入结束时,均质土和非均质土中导管总贯入阻力分别减小42.60%,28.48%;导管划井眼时的上下循环运动,增大了土体的"累积剪切位移",使得管土界面之间的摩擦疲劳增大,导管贯入阻力降低,使得"卡住"的导管可以继续贯入到设计深度。

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.