Study on Punch-Through Prediction and Risk Control Method of Jack-Up Spudcan
- Hao Xu (CNPC Engineering Technology Research Company Limited) | Zhenwen Liu (CNPC Engineering Technology Research Company Limited) | Lei Qi (CNPC Engineering Technology Research Company Limited) | Haifeng Deng (CNPC Engineering Technology Research Company Limited) | Chun Li (CNPC Engineering Technology Research Company Limited)
- Document ID
- International Society of Offshore and Polar Engineers
- The 28th International Ocean and Polar Engineering Conference, 10-15 June, Sapporo, Japan
- Publication Date
- Document Type
- Conference Paper
- 2018. International Society of Offshore and Polar Engineers
- multi-layered soil system, risk control, Jack-up rig, punch-through analysis
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- 21 since 2007
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Jack-up rig installation is often faced with potential punch-through problems, which could produce fatalities on the legs or jacking systems. Thus it is essential to perform installation safety assessment on site specifically before deployment. This paper proposes a punch-through prediction method for spudcan penetration in multi-layered soil system. Limit penetration depth of jack-up spudcan is analysed based on finite element method for leg structure strength. The more improved punch-through analysis process is discussed. Finaly, The accuracy of the method is verified by the analysis of the actual process. Potential punch-through is reasonably predicted.
Prior to the installation of a mobile jack-up spudcan, an assessment is needed to confirm the depth of penetration under preload, and to identify any punch-through risk (SNAME, 2002). Once the punch-through happens, it may cause damage to the legs even the hull. So, when the soil profile consists of “stiff or hard shell”, that is stiff overlying soft thin layer, the potential punch-through is a serious threat to the jack up legs.
The bearing capacity of the “hard shell” included in the seabed soil profiles is influenced by the underlying soft soil layer, and the bearing capacity will be generally weakened. In reality, there is an infinite variety of soil profiles, and a literature review reveals that the footing bearing capacity in single and two-layer system has been widely investigated. For example, Brinch Hansen (1970), Houlsby and Martin (2003) and Hossain et al. (2006) studied the footing capacity in single clay or sand layer, while Meyerhof and Chaplin (1953), Meyerhof and Hanna (1978) and Teh et al. (2009) provided solutions for two-layer system, aiming at identifying soil squeezing or punch-through mechanisms.
In this paper, a study has been performed to assess penetration resistance of jack-up spudcan in multi-layered soil system (> 3 layers). Based on the existing single and two-layer bearing capacity analysis methods, the bearing capacity of multi-layered soil system is corrected from the bottom to the top layer one by one. In order to improve the accuracy of the calculation results, the method of calculating the cavity depth in soil is also dicussed.
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