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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

Case Study of Underwater Cutting Steel Pile Technology for an Offshore Jacket Structure
Wei Zhang1, Fei Wang1, Puyang Zhang2
1. Yantai Salvage Bureau Technology Center, Ministry of Transport
Yantai, Shandong, China
2. State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin UniversityTianjin, China

is designed to match the abrasive water jet cutting process for high-level
cutting operations.

ABSTRACTThe steel pile foundation of an offshore jacket structure was cut underwater, an underwater adjustable leveling cutting tool is designed tomatch the abrasive water jet cutting process for high-level cutting
operations. It solves the levelness requirements of the steel pilefoundation underwater cutting and the relative height difference
requirements of the four steel piles. The final cutting accuracy reached asingle pile level ≤1%, the relative elevation of the four steel piles was<50mm, and the level of the new jacket after installation was 0.96‰.

ENGINEERING BACGROUND
An offshore jacket has a four-leg pile foundation, and the post-piling
method is adopted for foundation installation. For the steel pile top
elevation difference, the allowable deviation is less than 200mm
according to the design requirements. Due to some special reasons, thewhole jacket was dismantled and reinstalled. The original steel piles
were used as the foundation in the original position, and the new jacket
was installed using the pile-first method. Demolition requires that thecutting position of the jacket is not higher than the top of the steel pile.
After the jacket is removed, the verticality of the steel pile and theelevation of the top of the pile are measured. According to themeasurement results, the steel pile tops are cut so that the relative
elevation difference of the four steel pile tops is less than 50mm, thelevelness of the top of each steel pile after cutting is less than 1%, andthe levelness of the new jacket after installation is less than 1.5‰.

KEY WORDS: Underwater cutting; abrasive water jet cutting; cutting
accuracy; pile top levelness.

INTRODUCTION
During the construction of the jacket, it may happen that the steel piles
are not in place or the top elevation of the steel piles does not meet thedesign requirements and is difficult to solve by re-driving. In this case,steel pile cutting is the fastest and safest process. In the construction ofocean engineering, the underwater cutting processes for steel piles withlarger wall thickness and higher precision include diamond wire saw
cutting, abrasive water jet cutting and new underwater laser cutting
technology (Gong, 2016; Sun et al., 2013; Wang et al., 2015; Wang etal., 2019), no matter which cutting process, adaptation tooling is the keyequipment, and its adjustment accuracy is related to the underwater
cutting accuracy. At present, domestic laser underwater cutting is still in
the laboratory verification stage (Wang et al., 2020), and there is littleengineering practice. The diamond wire saw cutting machine is affectedby its structural size, and has certain requirements for the diameter andstructure of the steel pipe pile to meet the construction process (Wang etal., 2016). The abrasive water jet cutting equipment is equipped withreasonable tooling for high-precision underwater cutting, which makes
it easier to realize the operation process. Underwater cutting of the steel
pile foundation of a jacket structure, focusing on controlling the level ofsteel pile cutting and the relative elevation of the four steel piles. For thepurpose of this operation, an underwater adjustable leveling cutting tool

PROCESS DESIGN
During the piling operation, one steel pile failed to reach the design
elevation, so the pile was cut. The pile top elevation is quite different
from the other three steel pile top elevations. If the failed pile top
elevation is used as a reference, it is difficult for the same tooling to meetthe cutting requirements of four steel piles. For this reason, the design
takes the original jacket main pile grouting barrel bell mouth as thereference elevation to carry out the underwater cutting operation of thesteel pile, so that the elevation of the steel pile top after cutting meets thedesign requirements. The steel pile parameters are shown in Table 1.
Table1. Steel pile parameters (unit: mm)
Parameter

297

Diameter

WallthicknessHorn diameter oforiginal jacket mainpileWorking
water depth