Seabed normal reaction force is calculated using a quadratic function of pipe penetration. Seabed resistance to lateral movement is calculated using a model which incorporates initial breakout of pipe from its original position and growing berm resistance as additional soil mass is accumulated in front of the pipe as pipe moves laterally. By selecting appropriate values for these parameters, both monotonic as well as non-monotonic resistance functions can be modelled. The following figure presents two examples.
The derivative of this function is used to calculate the tangent stiffness contributions