What is Leg Punch Through (Rapid Penetration) for Jack Up Rigs ?

Leg punch through which is one of the biggest dangers of a Jack Up is happened when a jack up leg or more legs rapidly penetrates into formation underneath a spud can(s). This will result in damage in legs, loss of balance of a rig, and potential harm people life.  Whether higher environmental loads or larger water depths, this increases demand on Jack Ups, leads to higher elevated weights, and creates more pronounced consequences of a punch. As depth increases, so does a typical soil’s bearing capacity. Soil strength also sees a rapid reduction when a soil layer is underlain by a weaker layer. The weaker soil eventually gives way as the spud can reaches the interface and the jacking system can’t cope with the speed at which the support of the leg moves downwards; the leg isn’t able to maintain the hull level. The hull then sways after it rotates and bends the legs. Relative to the supports, a weight shift occurs and to maintain equilibrium the required footing reaction increases. This process will only end when any hull buoyancy (from the hull now in the water) or the soil’s bearing capacity allows an equilibrium to be reached.

Figure 1 - Soil Bearing

Figure 1 – Soil Bearing, Apvandenberg.com. (2008).

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