Improved Surface Drainage of Pavements Final Report (1998) / Chapter Skim
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Chapter 1 Introduction
Chapter 1 Introduction
Pages 1-10
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. A literature review to establish the state of practice regarding analytical models for predicting rainfall water depths and to establish current design practices for removing rainfall runoff from multilane pavements.
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Skid resistance measurements to supplement current hydroplaning data in the literature and to better quantify the onset of hydroplaning as a function of the depth of the water film flowing over the pavement surface. Desian procedures and criteria that can be used bv user agencies In the selection of the most cost-effective means for controlling surface drainage and incorporate the procedures and criteria into a computer program.
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Thus, the maximum flow path for a pavement section is the longest flow path for the section-the maximum distance that a rainfall droplet can flow between the point of contact with the water film and its point of exit from the pavement, as presented in figure 2. For a given quantity of rainfall per unit area of pavement, reducing the flow path will result in a more shallow depth of flow and a concomitant reduction in the propensity for hydroplaning or excessive splash and spray.
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Definition of water film thickness, mean texture depth, and total flow.
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=. 0 1 2 3 4 Water exits design plane '~low 1 Rainfall drop enters pavement surface at comer Distance across plane, m Note: The figures above show a plan view of a design plane (nght)
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This fact necessitated the measurements of Manning's n for some selected surfaces for which data was not available In the literature. Methods for Reducing Water Film Thickness There are five techniques that can be used to reduce water film thickness: alteration of surface geometry, installation of drainage appurtenances, use of permeable or porous asphalt paving mixtures, grooving (portland cement concrete)
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pavements also provide a means for reducing water film thickness. Research Program The research program that was followed during this study was designed to provide the additional data needed to implement the methods that were identified for reducing water film thickness, to provide models that predict the depth of sheet flow when these techniques are used, and to provide guidelines so that the design engineer can facilitate their implementation.
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Evaluation and Model Refinement I I Task 6. Development of Guidelines ~ 1 Environmental Factors Pavement Geometry Appurtenances Material Properties Models: - Sheet flow - Skid resistance - Hydroplaning Task 3.
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By selecting maximum allowable water film thicknesses that can be allowed without the onset of hydroplaning, the design engineer can use the proposed design guidelines to select and specify the pavement geometry, surface characteristics and mixture type, and appurtenance design required to satisfy the hydroplaning criteria. The design guidelines and associated computer program allow the design engineer to select pavement geometries that minimize sheet flow; to select and locate drainage appurtenances; and to select various mixture types and surface textures that will also minimize water film thickness and the potential for hydroplaning.
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The "Proposal Design Guidelines for Improving Pavement Surface Drainage" and the PAVDRN program are available from NCHRP via the ~nternet and present detailed descriptions of several of the experiments to determine Man~g's n.
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