Session: 10-05-01 Bucket Foundations, Suction Caissons and Spudcans

Paper Number: 102040

102040 - Decommissioning Analysis for Suction Caisson Foundations 

Authors: Sharma¹, L., Bubel¹, J. 

¹ Ramboll Deutschland GmbH, Jürgen-Töpfer-Straße 48, 22763 Hamburg 

Abstract:

Suction caisson foundations are considered to be an economic alternative to piled foundations to support offshore jackets, especially in situations where there is shallow bedrock. Over the last few years significant advances in the design of suction caissons have developed, leading to a strong increase in installed suction caissons. One ecologic benefit of this type of foundation is the possibility of a complete removal at the end of its lifetime with today's technology.

The removal of a suction caissons follows a reverse installation procedure. The CPT-based method with site-specific soil resistance factors is preferably calibrated using trial installations. However, the decommissioning needs to also consider the soil's aging effects and marine growth, which can result in yet unknown additional forces. 

This paper presents the methodology of the decommissioning analysis for suction caissons in sandy and layered soils, which was applied to an Offshore Wind Farm in the North Sea. Due to data restrictions, the method is explained using artificially generated CPT logs and synthetic trial installation recordings. The frictional forces are assessed using a simple CPT-approach (DNVGL, 2017) with back-calculated soil resistance factors from synthetic on-site trials. The considered aging effects are soil type specific with an approach for sand following Lehane et al. (2017) and for clay based on NGI (2013). 

References 

a.       DNVGL-RP-C212- Offshore soil mechanics and geotechnical engineering, DNVGL, August 2017

b.       Lehane, Barry & Lim, Jit & Carotenuto, Pasquale & Nadim, Farrokh & Lacasse, Suzanne & Jardine, Richard & Dijk, Bas. (2017). Characteristics of Unified Databases for Driven Piles. 8th International Conference of Offshore Site Investigation and Geotechnics (OSIG 2017). 

c.       Time Effects on Pile Capacity (2013). NGI report no: 20061251-00-279-R 

Keywords 

Suction caissons, decommissioning, aging effects, offshore wind

Presenting Author: Lupamudra Sharma Ramboll

Presenting Author Biography: Miss. Sharma is a Junior Consultant in the Marine and Civil Engineering department at Ramboll Germany. She has a Masters in Geotechnical Engineering and another Masters in Structural Engineering. Her research interests include foundation design, offshore geotechnics and BIM of structures.

Authors:

Lupamudra Sharma Ramboll
Julian Bubel Ramboll