Permeable pavements: Sizing

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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 [1]

To calculate the maximum total depth of all aggregate layers needed for pavement support and water storage reservoir[edit]

The equation for the maximum depth of the stone reservoir (dr, max, mm) is as follows:

{{Plainlist|1=Where:

Where Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle RVC<sub>T</sub> = D \times i *''D'' = Duration of the design storm event event (hr) *''i'' = Intensity of the design storm event (m/hr) *''R'' = ''A<sub>i</sub>''/''A<sub>p</sub>''; the ratio of impervious contributing drainage area (''A<sub>i</sub>'') to permeable pavement area (''A<sub>p</sub>''). Note that the contributing drainage area should not contain pervious areas. R should not normally exceed 2. *''f''' = [[Design infiltration rate]] of underlying native soil (mm/hr) *''n'' = Porosity of the stone bed aggregate material (typically 0.4 for 50 mm dia. [[reservoir aggregate|clear stone]])}} On highly permeable soils (e.g., infiltration rate of 45 mm/hr or greater), a maximum stone reservoir depth of 2 metres is recommended to prevent soil compaction and loss of permeability from the mass of overlying stone and stored water. ===To calculate the invert of the underdrain from the base of the reservoir=== 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: <math>d_{r}=\frac{f'\times t}{n}}

Where:

  • f' = Design infiltration rate (mm/hr), and
  • t = Drainage time (hrs), e.g. 72 hours, check local regulations for drainage time requirements.
  • n = Porosity of clear stone

When sizing the area of permeable paving based on the contributing drainage area, the following equation may be used: Failed to parse (syntax error): {\displaystyle A_p=\frac{Q_c\times A_c}{V_R\times (d_p – P + (q'\times t))}}

Back to Permeable pavements

  1. Smith, D. 2006. Permeable Interlocking Concrete Pavements; Selection, Design, Construction, Maintenance. 3rd Edition. Interlocking Concrete Pavement Institute. Burlington, ON.