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The following calculation is used to size the stone storage bed (reservoir) used as a base course. It is assumed that the footprint of the stone bed will be equal to the footprint of the pavement. The following equations are derived from the ICPI Manual <ref>Smith, D. 2006. Permeable Interlocking Concrete Pavements; Selection, Design, Construction, Maintenance. 3rd Edition. Interlocking Concrete Pavement Institute. Burlington, ON.</ref>
The following calculation is used to size the stone storage bed (reservoir) used as a base course. It is assumed that the footprint of the stone bed will be equal to the footprint of the pavement. The following equations are derived from the Interlocking Concrete Pavement Institute (ICPI) manual <ref>Smith, D. 2017. Permeable Interlocking Concrete Pavements; Selection, Design, Specifications, Construction, Maintenance. 5th Edition. Interlocking Concrete Pavement Institute. Chantilly VA</ref>
===For full infiltration design, to calculate the total depth of clear stone aggregate layers needed for the water storage reservoir===
===For full infiltration design, to calculate the total depth of clear stone aggregate layers needed for the water storage reservoir===
The equation for the maximum depth of the stone reservoir (''d<sub>r, max</sub>'', m) is as follows:
The equation for the maximum depth of the stone reservoir (''d<sub>r, max</sub>'', m) is as follows:
<math>d_{r, max}=\frac{(RVC_{T}\times A_{p}) + (RVC_{T}\times A_{i}\times C) - (f'\times D\times A_{p})}{n}</math>
<math>d_{r, max}=\frac{(RVC_{T}\times R) + RVC_{T} - (f'\times D)}{n}</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*''D'' = Duration of the design storm event event (hr)
*''D'' = Duration of the design storm event event (hr)
*''i'' = Intensity of the design storm event (m/hr)
*''i'' = Intensity of the design storm event (m/hr)
*''R'' = the ratio of impervious contributing drainage area to permeable pavement area; ''A<sub>i</sub>''/''A<sub>p</sub>''
*''A<sub>i</sub> = Impervious contributing drainage area (m<sup>2</sup>)
*''A<sub>i</sub> = Impervious contributing drainage area (m<sup>2</sup>)
*''A<sub>p</sub> = Permeable pavement area (m<sup>2</sup>)
*''A<sub>p</sub> = Permeable pavement area (m<sup>2</sup>)
*''f''' = [[Design infiltration rate]] of underlying native soil (m/hr)
*''f''' = [[Design infiltration rate]] of underlying native soil (m/hr)
*''n'' = Porosity of the stone bed aggregate material (typically 0.4 for 50 mm dia. [[reservoir aggregate|clear stone]])}}
*''n'' = Porosity of the stone bed aggregate material (typically 0.4 for 50 mm dia. [[reservoir aggregate|clear stone]])
It is important to note that R should not exceed 1 to limit hydraulic loading and help avoid premature clogging. Also important to note is that the contributing drainage area should not contain pervious areas that are sources of sediment that can lead to premature clogging.
It is important to note that R should not exceed 2 to limit hydraulic loading and help avoid premature clogging. Also important to note is that the contributing drainage area should not contain pervious areas that are sources of sediment that can lead to premature clogging.
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===For partial infiltration design, to calculate the depth of the storage reservoir needed below the invert of the underdrain pipe===
===For partial infiltration design, to calculate the depth of the storage reservoir needed below the invert of the underdrain pipe===
For designs that include an underdrain, the depth of the storage reservoir below the invert of the underdrain pipe (''d<sub>r'') can be calculated as follows:
For designs that include an underdrain, the depth of the storage reservoir below the invert of the underdrain pipe (''d<sub>r'') can be calculated as follows:<br>
<math>d_{r}=\frac{f'\times t}{n}</math>
<math>d_{r}=\frac{f'\times t}{n}</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
Where:<br>
Where:<br>
A<sub>c</sub> = A<sub>i</sub> + A<sub>p</sub>
A<sub>c</sub> = A<sub>i</sub> + A<sub>p</sub>, and<br>
A<sub>r</sub> = A<sub>p</sub> (i.e., assumed that the water storage reservoir area and permeable pavement area are the same)
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Then increase A<sub>r</sub> accordingly to keep R between 0 and 2, which reduces hydraulic loading and helps avoid premature clogging. This assumes that the water storage reservoir area and permeable pavement area are the same (A<sub>r</sub> = A<sub>p</sub>).
Then adjust A<sub>r</sub> accordingly to keep R between 0 and 1, which reduces hydraulic loading and helps avoid premature clogging.
Back to [[Permeable pavements]]
Back to [[Permeable pavements]]
[[Category:Calculations]]
[[Category:Calculations]]