Browsing by Author "Klenzendorf, Joshua Brandon"
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Item Hydraulic conductivity measurement of permeable friction course (PFC) experiencing two-dimensional nonlinear flow effects(2010-05) Klenzendorf, Joshua Brandon; Charbeneau, Randall J.; Barrett, Michael E.; Maidment, David R.; McKinney, Daene C.; Sepehrnoori, Kamy; Sharp, Jr., John M.Permeable Friction Course (PFC) is a layer of porous asphalt pavement with a thickness of up to 50 millimeters overlain on a conventional impervious hot mix asphalt or Portland cement concrete roadway surface. PFC is used for its driver safety and improved stormwater quality benefits associated with its ability to drain rainfall runoff from the roadway surface. PFC has recently been approved as a stormwater best management practice in the State of Texas. The drainage properties of PFC are typically considered to be governed primarily by two hydraulic properties: porosity and hydraulic conductivity. Both of these hydraulic properties are expected to change over the life of the PFC layer due to clogging of the pore space by trapped sediment. Therefore, proper measurement of the hydraulic properties can be problematic. Laboratory and field tests are necessary for accurately determining the hydraulic conductivity of the PFC layer in order to ensure whether the driver safety and water quality benefits will persist in the future. During testing, PFC experiences a nonlinear flow relationship which can be modeled using the Forchheimer equation. Due to the two-dimensional flow patterns created during testing, the hydraulic conductivity cannot be directly measured. Therefore, numerical modeling of the two-dimensional nonlinear flow relationship is required to convert the measureable flow characteristics into the theoretical flow characteristics in order to properly determine the isotropic hydraulic conductivity. This numerical model utilizes a new scalar quantity, defined as the hydraulic conductivity ratio, to allow for proper modeling of nonlinear flow in two-dimensional cylindrical coordinates. PFC core specimens have been extracted from three different roadway locations around Austin, Texas for the past four years (2007 to 2010). Porosity values of the core specimens range from 12% to 23%, and the porosity data suggest a statistical decrease over time due to trapped sediment in the pore space. A series of constant head tests used in the laboratory and a falling head test used in the field are recommended for measurement of PFC hydraulic characteristics using a modified Forchheimer equation. Through numerical modeling, regressions equations are presented to estimate the hydraulic conductivity and nonlinear Forchheimer coefficient from the measureable hydraulic characteristics determined during experimental testing. Hydraulic conductivity values determined for laboratory core specimens range from 0.02 centimeters per second (cm/s) to nearly 3 cm/s. Field measurements of in-situ hydraulic conductivity vary over a range from 0.6 cm/s to 3.6 cm/s. The results of this research provide well-defined laboratory and field methods for measurement of the isotropic hydraulic conductivity of PFC experiencing two-dimensional nonlinear flow and characterized by the Forchheimer equation. This methodology utilizes a numerical model which presents a proper solution for nonlinear flow in two-dimensions.Item Hydraulic performance of bridge rails based on rating curves and submergence effects(2007-05) Klenzendorf, Joshua Brandon; Charbeneau, Randall J.The Texas Department of Transportation (TxDOT) is required by the Federal Highway Administration (FHWA) to use crash tested bridge rails on all new bridge construction and for existing bridges scheduled for safety rehabilitation. In general, crash tested bridge rails have a greater height and less open space than bridge rails that have failed crash testing. In the case of safety rehabilitation of existing bridge railing systems that have failed crash testing, the change to successfully crash tested rails would likely result in a rail design with greater height and less open space. This design could result in poor hydraulic performance of the new bridge rails during flood events, which may increase the upstream water surface elevation. Such a change could impact the floodplain for the 100-year return period flood. In the event that the floodplain changes by more than one foot, the Federal Emergency Management Agency (FEMA) requires a floodplain map revision. This can be costly and result in the delay and complication of rehabilitation projects. The objective of this research is to evaluate the hydraulic performance of different bridge rail designs that have been crash tested and found acceptable for TxDOT use. Physical modeling experiments are conducted in order to determine rating curves for various rail systems. The rating curves describe the upstream water surface elevation as a function of the flow rate passing over the rail. A simple three parameter model is developed in order to describe the rating curves based on obtained experimental data. In addition, the effects of the submergence of bridge rails by an increase in downstream water surface elevation are also evaluated. Submergence can occur on a rail located on the upstream side of the bridge due to the backwater produced by the rail on the downstream side of the bridge. This will increase the upstream water surface elevation predicted by the rating curves for each rail. Two different models are used to approximate and characterize the effects of rail submergence.