Behaviour of Cohesionless Soil During Cyclic Loading
Authors
Sørensen, Kris Wessel ; Nielsen, Søren Kjær ; Shajarati, Amir
Term
4. term
Education
Publication year
2012
Submitted on
2012-06-14
Pages
138
Abstract
En vedvarende udfordring i offshore geoteknik er at tage højde for cyklisk belastning (gentagne belastninger over tid). På grund af kompleksiteten findes der endnu ingen standardmetode, så området kræver mere forskning. Dette speciale undersøger, hvordan cyklisk belastning påvirker kohæsionsløse jorder (sand). Den undersøgte jord er marinsand fra et offshore-område ved Frederikshavn, Danmark, hvor et prototype suction bucket-fundament bærer en Vestas V90-3,0 MW vindmølle. Der er udført cykliske triaxialforsøg for at udvikle praktiske designdiagrammer, som kan anvendes ved dimensionering af nye offshore vindmøllefundamenter. Forsøgene viste, at størrelsen af den svingende belastning (cyclic load ratio), det gennemsnitlige belastningsniveau (average load ratio) og poretrykket (vandtrykket i jorden) har stor indflydelse på bæreevnen under cyklisk belastning. Derudover blev en avanceret materialemodel for sand (Modified Critical State Two-Surface Plasticity Model) implementeret i MATLAB for at simulere cyklisk jordadfærd. Den anvendte eksplicitte integrationsmetode viste sig ineffektiv og kan derfor ikke anbefales til en model af denne kompleksitet.
A persistent challenge in offshore geotechnical engineering is accounting for cyclic loading (repeated loads applied over time). Because the problem is complex, there is still no standard method and further study is needed. This thesis investigates how cyclic loading affects cohesionless soils (sand). The soil tested is a marine sand from an offshore site in Frederikshavn, Denmark, where a prototype suction bucket foundation supports a Vestas V90-3.0 MW wind turbine. We carried out cyclic triaxial laboratory tests to develop practical design charts that can be used when designing new offshore wind turbine foundations. The tests showed that the size of the fluctuating load (cyclic load ratio), the average load level (average load ratio), and the pore pressure (water pressure in the soil) strongly influence bearing capacity under repeated loading. We also implemented in MATLAB an advanced constitutive model for sand (the Modified Critical State Two-Surface Plasticity Model) to simulate cyclic soil behavior. However, the explicit integration scheme used proved inefficient and is therefore not recommended for a model of this level of complexity.
[This abstract was generated with the help of AI]
Keywords
Cyklisk belastning ; Sand ; Frederikshavn ; Offshore ; Triax
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