Changes

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>

===To calculate the maximum total depth of all aggregate layers needed for pavement support and 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_{r, max}'', mm) is as follows:  

The equation for the maximum depth of the stone reservoir (''d_{r, max}'', m) is as follows:  

 

{{Plainlist|1=Where:

{{Plainlist|1=Where:

*''RVC_T'' = [[Runoff volume control target]] (m)

*''RVC_T'' = [[Runoff volume control target]] (m)

<math>RVC_{T}= D\times i </math>

<math> RVC_T = D \times i

*''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'' = ''A_i''/''A_p''; the ratio of impervious contributing drainage area (''A_i'') to permeable pavement area (''A_p''). Note that the contributing drainage area should not contain pervious areas. R should not normally exceed 2.

*''R'' = the ratio of impervious contributing drainage area to permeable pavement area; ''A_i''/''A_p''

*''f''' = [[Design infiltration rate]] of underlying native soil (mm/hr)  

*''A_i = Impervious contributing drainage area (m²)

*''A_p = Permeable pavement area (m²)

*''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]])}}  

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.

===To calculate the invert of the underdrain from the base of the reservoir===

===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:

*''f''' = Design infiltration rate (mm/hr), and

*''f''' = Design infiltration rate (mm/hr), and

*''t'' = [[Drainage time]] (hrs), e.g. 72 hours, check local regulations for drainage time requirements.   

*''t'' = [[Drainage time]] (hrs), e.g. 72 hours, check local regulations for drainage time requirements.   

*''n'' = Porosity of [[Reservoir aggregate|clear stone]]}}

*''n'' = Porosity of the stone bed aggregate material (typically 0.4 for 50 mm dia. [[reservoir aggregate|clear stone]])}}  

----

----

When sizing the area of permeable paving based on the contributing drainage area, the following equation may be used:

Where the total contributing drainage area (A_c) and total depth of clear stone aggregate needed for load bearing capacity of the pavement are known (i.e., storage reservoir depth is fixed) or if available space is constrained in the vertical dimension due to water table or bedrock elevation, the minimum footprint area of the water storage reservoir, A_r can be calculated as follows:<br>

<math>A_p=\frac{Q_c\times A_c}{V_R\times (d_p – P + (q'\times t))}</math>

<math>A_{r}=\frac{D(i - f')\times A_{c}}{d_{r} \times n}</math>

 

A_c = A_i + A_p, and<br>

A_r = A_p (i.e., assumed that the water storage reservoir area and permeable pavement area are the same)

Then adjust A_r 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]]