TY - JOUR

T1 - On the behavior of suction buckets in sand under tensile loads

AU - Thieken, Klaus

AU - Achmus, Martin

AU - Schröder, Christian

N1 - Funding Information: This study was partly carried out in the scope of the research project “WindBucket” funded by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety , Germany (BMU). The authors sincerely acknowledge BMU support.

PY - 2014/7

Y1 - 2014/7

N2 - Suction buckets can be used instead of driven piles for the support of jacket or tripod foundations for offshore wind energy converters (OWECs). However, due to the relatively small self weight of offshore wind structures, considerable tensile loads can occur for instance during storms; these loads usually govern the dimensioning of the buckets. Under rapid tensile loading, suction pressures are induced inside the bucket, which can considerably increase the tensile capacity. This paper presents results of numerical simulations based on a coupled pore fluid diffusion and stress analysis which allow for the description of the partly drained load-bearing behavior as well as the quantification of the tensile resistance. It is shown that a high pull-out rate leads to a large increase of the tensile capacity. The maximum capacity is reached when the soil behaves fully undrained or when cavitation of the pore water occurs. In this regard, the main influence parameters are the bucket geometry, the soil permeability, the pull-out rate (loading rate) and, regarding cavitation, also the water depth. It is shown that the mobilization of suction pressures requires a large heave of the bucket, which might be inadmissible with respect to serviceability requirements. Simulations in which variable tension loads are applied with a specific loading rate and then kept constant are also presented. It is found that an accumulation of heave over time occurs when the load exceeds the drained capacity of a bucket. This indicates that cyclic loading of buckets with tensile loads often exceeding the drained capacity might lead to excessive heave.

AB - Suction buckets can be used instead of driven piles for the support of jacket or tripod foundations for offshore wind energy converters (OWECs). However, due to the relatively small self weight of offshore wind structures, considerable tensile loads can occur for instance during storms; these loads usually govern the dimensioning of the buckets. Under rapid tensile loading, suction pressures are induced inside the bucket, which can considerably increase the tensile capacity. This paper presents results of numerical simulations based on a coupled pore fluid diffusion and stress analysis which allow for the description of the partly drained load-bearing behavior as well as the quantification of the tensile resistance. It is shown that a high pull-out rate leads to a large increase of the tensile capacity. The maximum capacity is reached when the soil behaves fully undrained or when cavitation of the pore water occurs. In this regard, the main influence parameters are the bucket geometry, the soil permeability, the pull-out rate (loading rate) and, regarding cavitation, also the water depth. It is shown that the mobilization of suction pressures requires a large heave of the bucket, which might be inadmissible with respect to serviceability requirements. Simulations in which variable tension loads are applied with a specific loading rate and then kept constant are also presented. It is found that an accumulation of heave over time occurs when the load exceeds the drained capacity of a bucket. This indicates that cyclic loading of buckets with tensile loads often exceeding the drained capacity might lead to excessive heave.

KW - Caisson

KW - Numerical simulation

KW - Offshore wind energy converter

KW - Sand

KW - Suction bucket

KW - Tensile capacity

UR - http://www.scopus.com/inward/record.url?scp=84899945694&partnerID=8YFLogxK

U2 - 10.1016/j.compgeo.2014.04.004

DO - 10.1016/j.compgeo.2014.04.004

M3 - Article

AN - SCOPUS:84899945694

VL - 60

SP - 88

EP - 100

JO - Computers and geotechnics

JF - Computers and geotechnics

SN - 0266-352X

ER -