Physical modeling of subgouge deformations in sand

Yang, Wei (2009) Physical modeling of subgouge deformations in sand. Masters thesis, Memorial University of Newfoundland.

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Abstract

A series of 7 tests of PIRAM (Pipeline Ice Risk Assessment and Mitigation) tests were carried out to simulate the progress of a gouging ice keel by centrifuge modeling. This thesis focuses on the subgouge deformations of the ice gouging process. The relationships between gouge depth, frontal berm, force, pressure, subgouge deformation and vertical extent of subgouge deformation are discussed in the thesis. The PIRAM tests were compared with the results of a similar series of previously conducted tests, and previous tests. Significance of the frontal berm height, gouge depth, gouge rate are also discussed. -- The experimental program consisted of towing a model ice keel across a model testbed at a set gouge depth under various centrifuge acceleration. The test setup consisted of an aluminum half width ice keel model mounted on a gantry situated on top of the containment box given the centerline of the model was replaced by a viewing window to visualize the subgouge deformation accumulation. The model tests were conducted using saturated fine sand simulating seabed. Two tests were conducted with shallow gouge depths for comparison with previous Delft Hydraulics flume medium scale gouge tests to evaluate the applicability of centrifuge modeling. Three tests were conducted at a fast gouge rate since most of the previous work were conducted at a relatively slow rate. A large amount of data regarding ice keel gouge in sand was acquired from the experimental program the analysis of which described here in. -- The combined depth of gouge depth and frontal berm height has a significant effect on the force and subgouge deformation. The force per unit width increases as the gouge depth increases. The vertical to lateral gouge force ratio seems to be independent of the aspect ratio which is gouge width divide gouge depth or attack angle. The kappa value is the frontal berm height normalized by gouge depth is linear with the aspect ratio. The kappa value has a significant effect on gouge force and subgouge deformation. Particle image velocimetry (PlV) technique was successfully used to track the evolution of subgouge deformation in all 7 tests. The maximum horizontal subgouge displacement occurred at the base of the keel and decreased with depth. The associated maximum gouge forces are a function of the keel attack angle and the gouge geometry. In comparison with previous tests, the vertical extent of subgouge deformation (SGD) was a function of combined depth and the soil state, but independent of the attack angle. The SGD are influenced by the attack angle and the soil state. Faster gouge rates may result in larger gouge forces by a factor of 2 to 3 and smaller horizontal subgouge deformations but similar vertical extent.

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