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mLine 1:
Line 1: − + − + − + − + − *''Q<sub>c</sub>'' = Depth of runoff from contributing drainage area, not including permeable paving surface (m) + − + − *''P'' = Rainfall depth (m) − + + − + + − + − ---- − (f') used in the above equations should be the [[design infiltration rate]] that incorporates a safety correction factor. 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. − + + +
Sahlla Abbasi moved page Permeable paving: Sizing to Permeable pavements: Sizing: Updating terminology for permeable pavings to permeable pavements
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 taken 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 taken 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>
===To calculate the total depth of the stone reservoir (all graded layers)===
===To calculate the total depth of the foundations (all aggregate layers)===
The equation for the depth of the stone bed is as follows:
The equation for the depth of the stone foundation (''d<sub>f, max</sub>'', mm) is as follows:
<math>d= \frac{[Q_c\times R + P - f'\times t ]}{V_{R}}</math>
<math>d_{f, max}=\frac{\left[\left ( RVC_{T}\times R \right )+ RVC_{T}-\left(f'\times t\right )\right]}{V_{R}}</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*''d'' = Stone bed depth (m)
*''RVC<sub>T</sub>'' = [[Runoff volume control target]] (mm)
*''R'' = ''A<sub>c</sub>''/''A<sub>p</sub>''; the ratio of contributing drainage area (''A<sub>c</sub>'') to permeable paving area (''A<sub>p</sub>''). Note that the contributing drainage area (''A<sub>c</sub>'') should not contain pervious areas. R should not normally exceed 2.
*''R'' = ''A<sub>c</sub>''/''A<sub>p</sub>''; the ratio of contributing drainage area (''A<sub>c</sub>'') to permeable paving area (''A<sub>p</sub>''). Note that the contributing drainage area (''A<sub>c</sub>'') should not contain pervious areas.
*''f''' = [[Design infiltration rate]] (mm/hr)
*''f''' = Design infiltration rate (m/day)
*''t'' = Time to fill stone bed (typically 2 hr)
*''t'' = Time to fill stone bed (typically 2 hr)
*''V<sub>R</sub>'' = Void ratio for stone bed (typically 0.4 for 50 mm dia. [[reservoir aggregate|clear stone]])}}
*''V<sub>R</sub>'' = Void ratio for stone bed (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===
===To calculate the invert of the underdrain from the base of the reservoir===
For designs that include an underdrain, the maximum depth of the stone reservoir below the invert of the underdrain pipe (''d<sub>s, max</sub>'') can be calculated as follows:
For designs that include an underdrain, the maximum depth of the storage layer below the invert of the underdrain pipe (''d<sub>s, max</sub>'') can be calculated as follows:
<math>d_{s, max}=\frac{f'\times t}{0.4}</math>
<math>d_{s, max}=\frac{f'\times t}{0.4}</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*''f''' = Design infiltration rate (mm/hr), and
*''f''' = Design infiltration rate (mm/hr), and
*''t'' = [[Drainage time]] (hrs), e.g. 96 hours, check local regulations for drainage time requirements.
*''t'' = [[Drainage time]] (hrs), e.g. 96 hours, check local regulations for drainage time requirements.
*''0.4'' = Void ratio of [[reservoir gravel|clear stone]]}}
*''0.4'' = Void ratio of [[Reservoir aggregate|clear stone]]}}
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When sizing the area of permeable paving based on the contributing drainage area, the following equation may be used:
When sizing the area of permeable paving based on the contributing drainage area, the following equation may be used:
<math>A_p= \frac{Q_c\times A_c}{V_R \times dp – P + q'\times t}</math>
<math>A_p= \frac{Q_c\times A_c}{V_R \times dp – P + q'\times t}</math>
[[category:modelling]]
Back to [[Permeable pavements]]
[[Category:Calculations]]