Jetting Effect of Jackup on Actively Punching Through Overlaid Sand Layer

摘要

A hazard of uncontrolled leg punch-through always exists when a sand soil layer with insufficient bearing capacity to support the jackup rig overlies a weaker soil layer. Failure to mitigate this hazard may lead to severe consequences: damaging the legs or collapsing the rig. Hence it always needs to actively penetrate through the overlaid strong soil layer so the spudcan can locate the lower stable holding layer. Other than the so-called Swiss cheese drilling being applied to the overlaid strong clay layer, the jetting system usually equipped with jackup rigs is expected to play an active role in assisting the spudcan to successfully penetrate through the overlaid sand layer. In such a case, a prior assessment of the jetting effect on weakening the sand soil layer is quite important so that the geotechnical engineers can decide whether the jetting operation is feasible enough at a specific site. To provide a reference to the offshore industry in such conditions, this paper proposes a theoretical model to analyze the effect of such a jetting system on decreasing the bearing capacity of the overlaid sand layer; the corresponding numerical and experimental results were also presented and discussed.