The Measures Against the Punch-Through on “HAKURYU 9”

Abstract

The self elevating offshore drilling platform “HAKURYU 9” observed further penetration of the rig's legs after preloading operations were completed at the Bay of Bengal.
On the 19th June 1987, “HAKURYU 9” commenced drilling operations under the leg penetrations 1) 3.90 2) 4.10 3) 4.60 metres.
By the 2nd July leg penetrations had increased to 1) 5.47 2) 5.13 3) 5.55 metres when drilling was suspended and the rig preloaded again.
However, the leg penetrations continued after resumption of driling, and developed the potential risk of punch-through foundation failure.
On the 12th August, the penetrations reached to 1) 7.53 2) 7.60 3) 7.94 metres and decision was made to suspend drilling activities, secure the rig and start leg jetting untill leg penetrations into the clay zone below 15.8 metres were achieved. It was understood that at this location there were approximately 4m of silty sand followed by silt to 15.8m and soft to firm clay to 35.6m.
This report will introdue the states of the penetrations and the jetting operations mentioned above and inquire into the cause of penetrations.