A master thesis from Aalborg University
Modelusikkerhed ved jordskælvsdesign af sænketunnel
[Model accuracy in aseismic design of immersed tunnel]
Author(s)
Term
4. term
Education
Publication year
2008
Submitted on
2008-06-10
Pages
161 pages
Abstract
This thesis deals with the model accuracy for seismic design of immersed tunnels, like the proposed underwater artery in Thessaloniki, Greece. The soil response to seismic waves is analysed in the frequency domain by means of the domain transformation method and the finite element method. The seismic response of an immersed tunnel and the damage in the gasket joints have been calculated with a closed form solution, a Winkler-type model, and a full three-dimensional continuum model. The Winkler model and the continuum model are applied in the time domain. Focus is especially given to the diverging results from the Winkler model, commonly used in seismic design, and the continuum model, which is considered to be more accurate. Through comparative analyses it is shown that the presented Winkler model is not able to model retroaction from the tunnel to the soil. This entails that the presented Winkler model is not suited for seismic design of an immersed tunnel with non-uniform cross section. Sensitivity analyses are performed to analyse the influence of the many parameters which must be determined for a seismic design. It is shown that the stratification and the soil parameters, together with the earthquake magnitude, influence significantly on the tunnel damage. On the other hand, the modelling of the immersed tunnel gasket joints has very little influence on the calculated gasket deformation. Finally, it is shown that the critical direction of wave propagation is an angle of approximately degrees to the tunnel axis.
Dette afgangsprojekt omhandler modelusikkerheder ved jordskælvsdesign af sænketunneler, med en sænketunnel i Thessaloniki i Grækenland som case. Jordens respons som følge af jordskælvsbølger er analyseret i frekvensdomæne ved hjælp af domænetransformationsmetoden og finite element metoden. Responset af sænketunnelen og skaderne i koblingerne mellem tunnelelementerne er beregnet med en løsning på sluttet form, en model af Winkler-typen samt en fuld tredimensionel kontinuummodel. Analyserne med de sidste to modeller foregår i tidsdomæne. Winkler-modellen anvendes ofte ved jordskælvsdesign, mens kontinuummodellen er anset for at være mere nøjagtig. De to modeller giver meget forskellige resultater, og årsagen til denne forskel er undersøgt nøje. Gennem sammenlignende analyser er det vist, at den opstillede Winkler-model ikke er i stand til at modellere tilbagekobling fra tunnelen til jorden. Dette indebærer at den opstillede Winkler-model ikke er egnet til at designe en sænketunnel med fleksible koblinger mod jordskælv. Ved design mod jordskælv er der mange parametre der skal bestemmes. For at undersøge hvor nøjagtigt disse parametre bør bestemmes er der udført følsomhedsanalyser. Det er vist at lagdelingen, jordens parametre samt jordskælvets størrelse har stor indflydelse på den beregnede skade på tunnelen. På den anden side har det meget lille betydning for skaden på tunnelen, hvordan det vælges at modellere koblingerne mellem tunnelelementerne. Endelig er det vist at den kritiske udbredelsesretning for jordskælvsbølgen er en vinkel på omtrent 45 grader med tunnelens længdeakse.
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