Geometric factors in roadway drainage

Abstract

Optimal drainage of roadways is crucial for safety, comfort, and economics. Lack of drainage results in reduced friction, lowered visibility, and ponded water creating danger and (at the least) nuisances to overall road users and the owners of nearby properties. In the long run, deterioration in roads follows as the standing water gets in in warmer climates and snowmelt expands in colder with the following frost damages; these decline driving safety and comfort for the second time in addition to the added cost of reconstruction and rehabilitation of the roadway. Thus, considerations regarding roadway drainage are an indispensable part of roadway design for both the overall safety of users and properties and the longevity of the roadway itself. Roadway flow takes two forms: over-lane (i.e., overland) flow and gutter flow (i.e., channel flow) adjacent to the curb. Thus, roadway drainage encompasses both overlane flow thickness optimization and controlling gutter flow. This dissertation investigates the most efficient and effective slope orientation for roadways of various widths, environmental conditions, and functionalities to establish necessary draining. That encompasses producing a physically based model for over-lane flow depth to investigate hydroplaning risks based on slope orientation; to examine the correctness of the common perception that inlet capacity is what controls inlet spacing. It also aims to frame the existing flush curb opening inlet studies within their scope and determines the missing parts to the most commonly used guidelines. While there are studies concerned with the sideway gutter flow and its spread, the flow contributing to hydroplaning directly from the roadway surface is less studied, and the geometric limits to antihydroplaning values are not well established. This work employs a kinematic wave equation (KWE) and provides a model to calculate water depth for the over-lane flow. The flow depths obtained via the new model are compared with antihydroplaning flow depths to find optimal cross slopes for various combinations for given longitudinal slopes. Establishing hydroplaing-free roads is the first step in establishing safe roads. A large amount of literature focuses on limiting the flow spread from the curb for a range of cross slope values; this leads to various flow depths due to of altered cross section, but the standards seem to fall shy in controlling the depth of flow. HEC-22, the urban drainage design manual of the US Department of Transportation, endorses limiting the flow depths to curb height and fixes the criterion for the inlet spacing to maximum allowable flow spreads. HEC-22 also recommends inlet spacing to be between 90-150 m. The common perception is that inlet capacity controls inlet spacing, but the impact of slope orientation under given criteria (such as a particular depth limitation) does not get much attention. This work, with no regard to inlet capacity but using the antihydroplaning configurations from the earlier part, analyzes maximum allowable inlet spacings and compares them to HEC-22's inlet spacing recommendation of 90-150 m to show any orientation that needs consideration beyond inlet capacity in xxiv designing inlet spacing. Maximum allowable inlet spacings are obtained for fixed maximums to flow depth and spread for the channel flow, and fixed maximums to over-lane water film thickness. The impact of slope orientation on inlet spacing was then analyzed. Having the results for varying slope orientations is crucial especially in changing terrains where perhaps each inlet spacing needs updating with changing slope, and spacing is critical for optimal drainage. The sizing of inlets under various slope orientations is important as the capacity varies with slope orientation. Curb opening inlets, the vertical openings at curbs, were investigated in this work also, for they noninterfere with the roadway and nonclog being a secure and effective candidate to most areas. A detailed analysis of the foundational models of curb opening inlets is presented for various geometric designs of flush orientations located on-grade. These geometries/types include simple vertical openings on curbs, openings with warped pavement in the close vicinity to increase capture capacity, and openings with not only the vicinity of the inlet depressed but also the approach gutter to increase drainage capacities further. The existing models were studied in detail and the misattributes to fundamental models were brought to the light. This work aimed to decrease the aftermath of inclement weather for the concerned partners from the bicyclist to the maintenance person via providing analyses to improve roadway drainage with the help of correct roadway slope orientation. This work contributes to (self) drainage by providing: 1) an easy to apply model for computing the over-lane flow depths so the geometries that are safe in terms of hydroplaning could be determined by any designer. 2) a detailed analysis of geometric configurations and putting forward not only which ones are safe in terms of hydroplaning but also which require attention in determining inlet spacing beyond the criteria of inlet capacity and maintenance purposes. 3) the details on curb opening inlet literature and investigating some inconsistencies regarding certain designs in what is probably the most commonly used manual (i.e. HEC-22).