Date of Award

1-1-2011

Document Type

Campus Access Dissertation

Department

Civil and Environmental Engineering

First Advisor

M H Chaudhry

Abstract

Sandbags have been widely used for flood control and for the closure of levee breaches due to their low cost and ease of use. However, the available information for determining the appropriate size for a typical application and research on the mechanics of motion of sandbag needed to optimize their placement are limited. The problem of the motion of sandbags in open-channel flow is complex since the sandbag shape varies from a very flat hump to spherical, sandbags may be porous and permeable, and the water content of the sandbag may vary from being totally dry to almost fully saturated.

The research reported in this dissertation investigates the forces affecting the sandbag motion in stationary liquid and in open channel flows. For this purpose, the drag force, the added-mass force, the settling velocity, the incipient motion, and the trajectories of different sandbags are studied. Digital Particle Tracking Velocimetry (DPTV) technique is used to estimate different parameters that affect the motion of sandbags.

A brief introduction to the topic and literature review are first presented. Then, the experimental investigations on the settling velocity of different sandbags are summarized. A methodology is outlined to estimate the drag and added-mass coefficients of sandbag-shaped particles by solving an equation describing the motion of a sandbag in stationary fluid. In addition, the effects of porosity and permeability of the sandbags on the settling velocity are investigated. Studies are summarized for the incipient motion of sandbags in uniform flow in a flume and for the effects of bed roughness, particle roughness, degree of saturation, shape factor, and on the initiation of particle motion. Equations and graphs for the critical parameters for initiating the motion of sandbags are presented. Tests for the incipient motion of sandbags are conducted in a complex flow field in the vicinity of the levee breach on a 1:50 scale model of the 17th Street Canal levee breach following Hurricane Katrina. Finally, the test results on the trajectories of sandbags in complex flow and in open channels are presented. The maximum settling distance for the sandbags of different size and type are estimated from the experimental data. For the trajectory of sandbags in open-channel flow, a numerical model is developed based on the solution of the Lagrangian equation for particle motion by the fourth-order Runge-Kutta method.

The results of this research will be useful for the planning, design and operation of projects for flood control, for the utilization of the sandbags in different applications and for developing more systematic procedures for levee breach closure.

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