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

New Approach for Penetration Resistance Calculation of Suction Bucket Foundation
Jiandong Xiao, Jialong Li
Shanghai Investigation, Design & Research Institute Co., Ltd
Shanghai, China

ABSTRACT

promote more efficient foundation types.

In this paper, a backstepping-based method is presented for calculating
the penetration resistance of offshore suction bucket foundations incomplex stratified geological environments. Penetration coefficients arecalculated for different soil strata using a binary linear regression
analysis between the variation in cone resistance (which is determinedby the CPT data) and the variation in penetration resistance (which isdetermined by in-situ installation records) at different penetration
depths. Based on the installation record of a small number of suction
bucket foundations, this method makes it possible to estimate thepenetration resistance of other suction bucket foundations built on agiven site.

Penetration of suction bucket foundation
A suction bucket foundation resembles a large upturned bucket, which
is sealed at the top with a lid. This type of foundation was utilized as ananchoring system for offshore platforms. It is considered to be an
efficient alternative to OWTs, which can cover a greater depth range of
5-60m at a lower cost (Wang et al., 2018). In addition, the advantagesof suction buckets include, but are not limited to, quick installation,
environmental awareness, easy decommissioning, and recyclability(Byrne et al. 2000). It has been successfully applied to projects at
Xiangshui (Jiangsu Province), Dafeng (Jiangsu Province), Rudong(Jiangsu Province), and Yangjiang (Guangdong Province) in China.

KEY WORDS: Suction bucket foundation; offshore wind turbines(OWTs); penetration resistance; CPT.

Suction bucket foundations are primarily installed in two stages. In thefirst stage, water is allowed to escape from within the bucket as it
penetrates the seabed under its own weight. Additional penetration isachieved in the second stage by pumping water out of the bucket which
creates downward pressure over the bucket top (and sidewall) and also
reduces the internal soil resistance due to the upward hydraulic gradients
through the soil plug. During installation, penetration resistance should
be determined in advance (1) to determine the bucket structure; (2) toevaluate the construction feasibility; and (3) to select the appropriate
water pump.

INTRODUCTION
Global offshore wind industry
The global offshore wind industry has experienced rapid growth in thepast few years due to increasing government attention to climate change.
In the past decade, the global offshore wind market has grown an averageof 22% per year, resulting in a total installation of 35.3 GW, which
represents 5% of the total global wind capacity by the end of 2020. For
the third consecutive year, China led the world in new offshore wind
installations, connecting more than 3 GW in 2020 (Lee and Zhao, 2021).
Nevertheless, the investment per megawatt (MW) in offshore windremains 50% higher than onshore wind. In order to play a significant rolein the future energy structure, offshore wind energy needs to reduce its
cost as much as possible.

The soil-structure interaction penetration resistance includes side shear
along the bucket wall as well as the bearing capacity of the wall tip. Aclassic approach is to relate the penetration resistance to the soil strength
index. For sand, the side shear force may be a function of sand-wall
friction angle δ (Houlsby and Byrne, 2005). For clay, the side shear force
may be related to the clay shear strength Su and a parameter α
representing soil sensitivity (DNV 2017). To determine the end bearing
capacity of sand and clay, bearing capacity factors must be determined.

In accordance with NREL's (National Renewable Energy Laboratory,USA) statistical data, for bottom-fixed offshore wind platforms, thesubstructure and foundations account for approximately 14.7% of thecapital expenditure (Wu et al. 2019). Therefore, it is important toThe other approach is based on the in-situ cone penetration tests (CPT).
Because the measured cone resistance qc automatically reflects the soil
characteristics and is linked directly to the tip and frictional resistance412