Design Guidelines - Grass

Design guidelines for grass-filled Truckgrid-Max

All of our design guidelines are written with best practice in mind.  It is strongly advised that any questions raised from the guidelines are directed to our technical team.

When Truckgrid-Max porous pavers are installed correctly to suit site conditions, they should provide source control within a SUDS system (Sustainable Urban Drainage Systems). Drainage must be a consideration when designing a construction profile to ensure that flood alleviation and water run-off is properly considered where natural infiltration may not be capable of withstanding all eventualities.

Questions to be considered

  • Does the proposed installation area drain well already?
  • Is there planned to be a slight fall to be built into the design to aid drainage, if aid is needed?
  • Is the drainage capability of the soils the same at the surface and at 200 - 500mm below the surface?
  • Have there been previous issues with drainage on site?
  • Has disposal of any excess water been considered?
  • Are there SuDS requirements to be considered?

We would advise speaking to our technical team regarding any of these questions for further guidance.


  1. If a geogrid is being considered as part of the construction profile, please ensure that at least 25% of the particle size of the sub-base is bigger than the mesh size to ensure good shearing/locking.
  2. The sub-base particle size ideally should not exceed 60mm and should be less than 5% fine material content of the whole. Please contact us if you would like any further guidance.
  3. Please refer to tables 1 & 2 for guidelines on the depth of sub-base for specific design profile to suit different site needs. Please note - if a geogrid is omitted, 50% of the depth of sub-base needs to be added to calculated depth with a geogrid. For example, 100mm with geogrid would become 150mm without.
  4. It is good practice to confine Truckgrid-Max plastic pavers on the site edges. This should be as strong as 150 x 150mm concrete kerbs due to the possible lateral loadings of heavyweight vehicles. The type of vehicles, frequency of traffic and circulation routes should all be considered when choosing the confinement method for Truckgrid-Max in the design.
  5. Truckgrid-Max has been designed to work within stated guidelines to a slope of 5% or less. Truckgrid can be used on steeper slopes in some cases - please enquire with our technical team for guidance.
  6. Ideally, the sub-base should extend out further than the surface area of Truckgrid-Max. This is so that lateral pressures caused by the traffic loading does not displace the Truckgrid-Max on the edges. The extension of sub-base outwards should be the same as the depth of the sub-base.  Please see the schematic for detail.
  7. Please refer to the installation guide for the filling of the cells and the best practice to ensure sustainable, healthy grass growth. Experience has shown that the best results are achieved in the longer term using a rootzone-type soil for the fill in the cells and an amenity grass seed mix.  Rolling in turf is not recommended.


Note on drainage

Any sub-base used in the construction profile should be permeable - for example, MOT Type 3. It should be predominantly fine material-free and able to compact well without losing integrity, stability and permeability/porosity. MOT type 1 should not be used. Please check with our technical team for guidance if an impermeable layer is already in place. For any detail on specification for design not covered in above, please get in touch with us.


Table 1 - Typical Sub-Base Thickness (with / without geogrid)

Application/ Load

CBR (%) Strength of subgrade soil

(T) DoT Sub-base Thickness (mm)

Fire truck and occasional HGV access

≥ 6

100

= 4 < 6

120

= 2 < 4

190

= 1 < 2

380

Light vehicle access and overspill car parking

≥ 6

100

= 4 < 6

100

= 2 < 4

135

= 1 < 2

260

 

Table 2 - Field Guidance for estimating sub-grade strengths

 

Consistency

Indicator

Product

Tactile (feel)

Visual

Mechanical (test)

SPT

CBR

%

CU

kN/sqm

 

Very Soft

Hand sample squeezes through fingers

A man standing will sink > 75mm

 

< 2

 

< 1

 

< 25

 

Soft

Easily moulded by finger pressure

A man walking sinks 50 – 70 mm

 

2 - 4

 

Around 1

 

Around 25

 

Medium

Moulded by moderate finger pressure

A man walking sinks 25mm

 

4 - 8

 

1-2

 

25 - 40

 

Firm

Moulded by strong finger pressure

A Utility truck ruts 10-25mm

 

8 - 15

 

2 - 4

 

40 - 75

 

Stiff

Cannot be moulded but can be indented by thumb

Loading construction vehicle ruts 25mm

 

15-30

 

4 - 6

 

75 - 100

 

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