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Title: Vertical drains as a countermeasure to earthquake-induced soil liquefaction
Author: Brennan, Andrew John
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2004
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Earthquake-induced soil liquefaction is a major cause of damage that needs to be controlled by engineers. A popular option for protecting against liquefaction is the installation of gravel drains to relieve generated excess pore pressures. A series of centrifuge tests were carried out on level sand beds without surface structures, to investigate qualitatively the effect of changing drain parameters and the geometry of drain groups. Using these, it was possible to determine a time varying extent of drain effectiveness, and a zone of influence consisting of a conical volume of soil from which draining fluid left the ground via the drain. Increasing drain radius was seen to increase the size of this zone but not accelerate drainage time if no other drains were near. It was also seen that fluid draining from depth caused a delay in the time for near-surface soil to begin draining. Limiting the influx of fluid from regions which are not to be protected was seen to be crucial to the success of small groups of drains. Soil with low permeability fine layers at the surface had identical pore pressure response to equivalent layers without such layers. However, the quantity of ejection features were greatly reduced by the presence of drains. To aid the modelling of deeper soil deposits, a new deep dynamic centrifuge container was designed and built. Analysis of the final box demonstrated that boundary interaction still occurred when the tested soil deviated from that for which it was designed. Drains were seen to be a temperamental method of achieving liquefaction protection, requiring very careful thought if excess pore pressures are to be kept below one. However, their acceleration of post-earthquake dissipation is a benefit in all cases. This may be made more optimal by allowing for the simple considerations presented herein.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral