Developing a Tool for the Design and Cost Optimization of Permeable Pavements in the Planning Stage of Stormwater Management
Type of DegreeMaster's Thesis
Civil and Environmental Engineering
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Stormwater runoff, when not managed properly, can represent a threat to the environment especially in today’s urban setting. For small pavement applications such as parking lots, conventional pavements and best management practices such as detention ponds are commonly used to address this issue. However, for such applications, there is currently an increase of interest in more sustainable options like Permeable Pavement (PP), which is a Green Infrastructure (GI) practice that helps store and treat stormwater runoff as well as support traffic loadings. Consequently, designers look for more efficient and economical ways to include PPs and other GI practices in their planning for stormwater management and compete with conventional systems, which are still perceived as the least expensive options. The product of this research is a tool called the “Cost Optimization Tool for Permeable Pavements (COTPP)” that will benefit Alabama municipalities and GI design agencies because it helps optimize the cost of PP systems for stormwater management. This tool contains the most reliable design methods (hydrological and/or structural) required to design three types of PP, which are Pervious Concrete (PC), Porous Asphalt (PA), and Permeable Interlocking Concrete Pavers (PICP). The COTPP also contains a cost optimization algorithm that helps combine permeable pavements with other types of GI, and conventional pavements to identify which combination will minimize costs and compete with conventional systems. Although the COTPP only supports three GI techniques, the algorithm was designed to be expanded to include other techniques in the future. Further, the COTPP was developed in a Microsoft Excel format because it is a computing tool that is available to most design engineers and decision makers. This will help reduce the need to invest in and learn complex modeling or optimization packages. A sensitivity analysis of the COTPP was performed to check the reliability of the design results and the efficiency of the tool. The analysis consisted of designing the three types of permeable pavements according to varying design inputs and comparing the results to recommendations from design guidelines or results from existing tools. The existing tools include PerviousPave from the American Concrete Pavement Association (ACPA) and the guidelines are from the National Asphalt Pavement Association (NAPA) and the Interlocking Concrete Pavement Institute (ICPI). For the structural design, it was found that the average percent differences between the design results of the COTPP and the results from the existing tools or guidelines are 4.4%, 7.2%, and 4.8% for PC, PA, and PICP, respectively. For the hydrological design, the results were the same for PC, PA, and PICP because they have the same design method in common. The average percent difference obtained between the design results of the COTPP and the results from existing tools is 15.1%. This number was particularly high because the hydrological design method used in the COTPP applies a factor of safety and a few different inputs which lead to more conservative results. It was concluded that the COTPP is a reliable tool that can be used confidently for the design of PPs. A case study was conducted to test the usefulness of the tool in terms of cost optimization of PPs. In the case study, an existing parking lot located in Alabama was selected and its construction costs were obtained from bid documents. The existing parking lot site was composed of PICP, a bioretention, and a HMA pavement. The costs were used in the COTPP to evaluate the capability of the tool to reduce the final construction cost of $305,918. The results showed that the actual cost of the parking lot ($305,918) could be reduced to as low as $238,790 using an alternative design where PICP occupies 11% of the parking lot area instead of the original 21% and the bioretention treats 90% of the total treatment volume. It was concluded, based on the results, that the cost of permeable pavements could effectively be optimized by the COTPP developed for Alabama designers and engineers during their planning stage. The unit costs of individual components (aggregate base, PC, PA etc.) that compose the parking lot and design constraints are the controlling factors in the optimization process.