Semester

Summer

Date of Graduation

2012

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Eduardo Sosa

Abstract

Tunnel safety deals with isolation of zone of disaster in case of flooding, fire, release of toxic gases and roof collapse. Disaster zone isolation, if successful, can result in lesser loss, in terms of human lives and revenue. An inflatable plugging system made of Vectran fiber was proposed to be installed at certain intervals of the tunnel length and deployed around the disaster zone for effective isolation. The study deals with a quarter-scale (of full scale) tunnel with plugging system for only flooding. It was tested at design pressure of plug and at limiting equilibrium conditions of both plug and tunnel pressures. The external loading was in terms of only water pressure to simulate the occurrence of flooding from superincumbent water way.;The inflatable plug was investigated under low pressure unconstrained inflation and high pressure confined inflation to study the elongation characteristics of its end caps in terms of longitudinal elongation. The front end cap of the plug was also scanned with a laser range finder at various levels of pressure up to the design pressure to obtain the 3--D surface and contour plot of the expansive nature of the surface under confined condition.;The primary function of the plug was to act as a floodgate by virtue of the friction between the plug surface and the tunnel wall developed by the normal force generated on the tunnel wall due to plug pressure. External pressure was applied on the plug in the form of confined water pressure. Real life possibilities of the plug slip was simulated in multiple experiments ranging from forced to unforced slip for which the friction coefficient of the system was evaluated. It was found that the plug slipped at a lower ratio of external to internal pressure than the pressure ratio of slip under normal condition with the reduction in effective contact length of the plug with the tunnel concrete. It was also found that the mass of the plug has variable impact on the occurrence of slippage from about 10%-50% of air by volume. The effect of abrasion of tunnel and plug surface was also evaluated which resulted in higher pressure ratios of slip than under smooth tunnel wall and plug surface.;Leakage characteristics of this plugging system were evaluated. The pressure ratio along with the plug positioning, plug surface characteristics and the level of oversizing of the plug were the main influencing factors. Since the dependency of leakage was on the above four factors, a range of leakage values were obtained for a single pressure ratio. A leakage mitigation device was employed but it showed inconclusive results due to its dependency on the above four factors simultaneously. Dependency of slippage on leakage was considered and hence the seepage water pressure study was considered.;Seepage water pressure study was conducted to measure the pressure of seeping water along various points of the cylindrical length of the plug at various circumferential depths. The variation of seepage pressure was linear from rear to front of the plug. It was also found that the coefficient of variation of the seepage water pressure at different depths of the circumference at the same longitudinal location increased from the rear of the plug to the front. This led to the understanding of the profile of the seepage water pressure. It was found to be axial at the rear of the plug, and both axial and circumferential (towards gravity) at other points along the cylindrical length. The water profile was evaluated in terms of loss of kinetic and gain in potential energy as well as the loss of head due to friction from plug webbing and tunnel wall.;The correlation between the occurrence of slippage and seepage water pressure was found to be inconclusive with the system friction coefficient reflecting similar values with the use of single layered Vectran plug. The presence of more abrasion on the plug surface on the front compared to the rear can be termed as an existence of correlation on the other hand.

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