Difference between revisions of "Permeable pavements: Sizing"

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===To calculate the maximum total depth of all aggregate layers needed for pavement support and reservoir water storage===  
 
===To calculate the maximum total depth of all aggregate layers needed for pavement support and reservoir water storage===  
The equation for the depth of the stone reservoir (''d<sub>r, max</sub>'', mm) is as follows:  
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The equation for the maximum depth of the stone reservoir (''d<sub>r, max</sub>'', mm) is as follows:  
  
 
<math>d_{r, max}=\frac{\left[\left ( RVC_{T}\times R \right )+ RVC_{T}-\left(f'\times D\right )\right]}{n}</math>
 
<math>d_{r, max}=\frac{\left[\left ( RVC_{T}\times R \right )+ RVC_{T}-\left(f'\times D\right )\right]}{n}</math>

Revision as of 16:25, 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 maximum total depth of all aggregate layers needed for pavement support and reservoir water storage[edit]

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

Where:

  • RVCT = Runoff volume control target (mm)
  • R = Ai/Ap; the ratio of impervious contributing drainage area (Ai) to permeable pavement area (Ap). 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)
  • D = Duration of the design storm event (e.g., 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.