Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Research on the Punch-through Analysis of Self-elevating Unit based on the Energy
Conservation Law
Hongtao Li, Jianbing Qu, Chang Gao
Offshore Engineering Technology Center of China Classification Society
Tianjin, China(Chen and Li, 2007; Chen, 2008). When the spud can of a Jack-up
encounters a stiff-over-soft soil layer during preloading, it is likely thatthe leg will rapidly drop through the upper stiff layer into the softer
underlying layer, which is punch-through (Kellezi and Stadsgaard,2012). For a Jack-up operating in deep water, punch-through during
preloading process may cause high speed tilting of the platform,
casualties, equipment damage, or even overturning of the wholeplatform. HSE (International Conference on Health, Safety andEnvironment) has found (Burd and Frydman, 1997) that punchthrough damage accounted for 53% of the total number of accidents,and every year occurrence of punch-through accident is increased by 1or 2. About 1 million USD to 10 million USD lost for one accident. InOctober 2009, when the “Sapphire Driller” carried out the preloadingin West Africa's Ivory Coast, punch-through of the bow leg happened
and several leg nodes were damaged by punching shear, so that theplatform tilted 7.8 degrees. In May 2009, in the course of preloading
operation for "HYSY941" in the South China Sea, the bow leg
piercing led bow inclination of 6.2 degrees and large deformation of 4
diagonal braces and two internal horizontal braces. Therefore, before
the jack-up preloading operation, leg penetration analysis should be
carried out. Especially in case of the risk of punch-through, moredetailed study must be executed and response measures be prepared to
avoid structural damage by punch-through.
In this paper, the four stages of punch-through, i.e. initial, balanced,continued and terminal, are considered according to the dynamic
characteristics of punch-through and applying the energy conservation
method, the gravitational potential energy is converted to the buoyancy
potential energy, leg deformation potential energy and potential energy
absorbed by seabed soil which can be calculated by the soil bearing
capacity for spud can. An equilibrium equation is built based on theabove theory to find out the maximum punch-through distance; Thenthe allowable punch-through distance is obtained by finite element
method, considering the leg strength, jacking system capacity and hull
structure; Finally, the safety of platform is checked by the comparisonof maximum punch-through distance and the allowable distance. As anexample, a Jack-up with 400ft working water depth is analyzed for alocation punch-through operation. The maximum punch-throughdistance and the allowable distance are calculated and safety
judgement is made for leg penetration. Based on the analysis result,

ABSTRACTThe punch-through of self-elevating unit is the accident during theperiod of preloading, which may cause platform over tilt, equipment
damage, and even cause personal casualty and platform overturning. In
order to analyze the punch-though process conveniently, the fourstages of initial, balanced, continued and terminal are consideredaccording to the dynamic feather of punch-through and applying theenergy conservation method, the gravitational potential energy isconverted to the buoyancy potential energy, leg deformation potential
energy and potential energy absorbed by seabed soil which can becalculated by the soil bearing capacity for spud can. An equilibrium
equation is built based on the above theory to find out the maximum
punch-through distance; Then the allowable punch-through distance isobtained by finite element method, considering the leg strength,
jacking system capacity and hull structure altogether; Finally, thesafety of platform is checked by the comparison of maximum punchthrough distance and the allowable distance. As an example, a Jack-up
with 400ft working water depth is analyzed for a location punchthrough operation. The maximum punch-through distance and theallowable distance are calculated and safety judgement is made for leg
penetration. Based on the analysis result, optimized preloading
program and risk control measures are advised. The above conclusion
is verified in practical jack-up leg penetration operation. The
calculation theory and method proposed in this paper for punchthrough of self-elevating unit have high application value, which issignificant for deep water Jack-up to reduce the risk of punch-through,and will provide strong guidance to the designers and operators of selfelevating unit.

KEY

WORDS: Self-elevating unit; punch-through; energy
conservation law; potential energy; buoyancy; leg deformation energy;
soil bearing capacity.
INTRODUCTION
Self-elevating unit is the platform whose main hull can be elevatedalong the leg to the certain height above the sea for drilling operation.
The Jack-up has been widely used in offshore oil and gas exploration
because of its high efficiency, convenient operation and low cost728