Back analysis of offshore pile driving with an improved soil model

Extensive back analyses of field records of offshore piles driven in calcar eous sands were performed using an improved soil model developed by Simons, The records were obtained during the installation of closed-end pipe piles for offshore platforms at the Northeast Pole site of the Campos Basin in B razil. This model is especially adequate for hard driving conditions when p iles are driven almost to refusal. In these cases, inertial (radiation) dam ping prevails, whereas viscous damping may be neglected. Back analyses with this model allowed the relative displacements between pile and soil to be calculated at various points along the pile in a one-dimensional finite-ele ment method solution. The soil stiffness k(s) and the damping coefficient c (s) were back-calculated for different pile depths. Values of the ratio of the shear modulus to the shaft resistance (G/r) were also back-calculated a nd suggestions are given concerning tentative values of this ratio to be se lected in drivability studies in calcareous sands.