Difference between revisions of "Permeable pavements: Sizing"

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m (Sahlla Abbasi moved page Permeable paving: Sizing to Permeable pavements: Sizing: Updating terminology for permeable pavings to permeable pavements)
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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 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 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>


===To calculate the total depth of the foundations (all aggregate layers)===  
===To calculate the total depth of the foundations (all aggregate layers)===  
The equation for the depth of the stone foundation (''d<sub>f, max</sub>'', mm) is as follows:  
The equation for the depth of the stone foundation (''d<sub>f, max</sub>'', mm) is as follows:  


<math>d_{f, max}=\frac{\left[\left ( RVC_{T}\times R \right )+ RVC_{T}-\left(f'\times t\right )\right]}{V_{R}}</math>
<math>d_{f, max}=\frac{\left[\left ( RVC_{T}\times R \right )+ RVC_{T}-\left(f'\times t\right )\right]}{n}</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*''RVC<sub>T</sub>'' = [[Runoff volume control target]] (mm)  
*''RVC<sub>T</sub>'' = [[Runoff volume control target]] (mm)  
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*''f''' = [[Design infiltration rate]] (mm/hr)  
*''f''' = [[Design infiltration rate]] (mm/hr)  
*''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]])}}  
*''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.
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.
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===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 storage layer below the invert of the underdrain pipe (''d<sub>s, max</sub>'') 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, max</sub>'') can be calculated as follows:  
<math>d_{s, max}=\frac{f'\times t}{0.4}</math>
<math>d_{r}=\frac{f'\times t}{n}</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. 72 hours, check local regulations for drainage time requirements.   
*''0.4'' = Void ratio of [[Reservoir aggregate|clear stone]]}}
*''n'' = Porosity 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 (d_p – P + (q'\times t))}</math>
 


Back to [[Permeable pavements]]
Back to [[Permeable pavements]]
[[Category:Calculations]]
[[Category:Calculations]]

Revision as of 15:44, 10 December 2021

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 total depth of the foundations (all aggregate layers)[edit]

The equation for the depth of the stone foundation (df, max, mm) is as follows:

Where:

  • RVCT = Runoff volume control target (mm)
  • R = Ac/Ap; the ratio of contributing drainage area (Ac) to permeable paving area (Ap). Note that the contributing drainage area (Ac) should not contain pervious areas. R should not normally exceed 2.
  • f' = Design infiltration rate (mm/hr)
  • t = Time to fill stone bed (typically 2 hr)
  • n = Porosity of the stone bed aggregate material (typically 0.4 for 50 mm dia. 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[edit]

For designs that include an underdrain, the depth of the storage reservoir below the invert of the underdrain pipe (dr, max) can be calculated as follows:

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.