Drivable Grass Guideline for Planted Infill Installation

Please read prior to installation, and have proper equipment and safety precautions in place.

For additional information please visit our website at www.soilretention.com or call 800-346-7995.

Installer Qualifications: An experienced installer, preferably certified by the Interlocking Concrete Pavement Institute (ICPI), and who has successfully completed installations of pavers or other pavement systems on projects of similar or larger scope and magnitude is recommended.

Planning: Final surface elevations and tolerances should be as specified on the project plans. Special consideration should be given to layout, slope, drainage, irrigation type/method, root barriers and edging/confinement.

1. Drivable Grass® Material Specification

  • Permeable, Flexible, Plantable Pavement System:
  • Nominal Dimensions in inches (l x w x h) :
  • Gross Area:
  • Weight:
  • Infill Volume:
  • Drivable Grass® Mats per pallet (each):
  • Area Covered per Pallet:
  • Color:
  • Flexibility (minimum radius of curvature in inches):

Drivable Grass®
24 x 24x 1.5
4 SF
45 lbs.
0.2 CF/Mat or 0.05 CF/SF
60
240 SF
Buff/Tan, Grey
12

2. Main Components of the Installation

  1. Subgrade Preparation/Subsurface Drainage (if required)
  2. Perimeter Confinement
  3. Geotextile Installation (if required)
  4. Base Material Installation
  5. Compaction
  6. Conventional Irrigation
  7. Bedding Installation
  8. Screeding
  9. Drivable Grass® Mat Placement
  10. Drip Tube Irrigation
  11. Infill
  12. Grass Installation

A. Subgrade Preparation

Excavate the installation area to the proper depth to allow for the structural pavement section below the Drivable Grass® installation in accordance with project plans and specifications. Complete any additional over-excavation and re-compaction as required to provide a firm and unyielding subgrade.

Where permeability of the subgrade is important, excavation is in native strong soils, and site conditions permit, compaction of the subgrade may be limited to trimming.

Test and approve the subgrade condition and provide written certification confirming the preparation, density and elevations conform to the project plans and specifications. Special consideration should be given for the following conditions:

  • Over-excavation depths and re-compaction of subgrade
  • Application of filter fabric over prepared subgrade (if required)
  • Sub-surface drainage due to low permeable subgrade (if required)

B. Perimeter Confinement

Keeping the edges of the Drivable Grass® installation contained is crucial for a successful long-term installation.

C. Geotextile Installation (if required)

Geotextile type should be in accordance with project plans and specifications. At a minimum, the geotextile should be placed at the bottom and sides of the sub-grade and secured in place to prevent wrinkling. Overlap at the seams of the geotextile should be a minimum of 12 inches.

D. Base Material Installation

Backfill, level, and compact the required base material to the density, depth/thickness and surface elevation in accordance with the project plans and specifications.

NOTE:  A proper aggregate base will contain a gradation of particles that will pack tightly together.

Local, state or provincial standards for aggregate base materials for roads should be used for the gradation and quality of dense-graded aggregate base materials. If no standards exist, follow ASTM D 2940, Standard Specification for Graded Aggregate Material for Bases or Subbases for Highways or Airports. The gradation for base material from this standard is given in the table below. This material should be compacted to a minimum of 95% Standard Proctor density per ASTM D 698 or local standards.

NOTE: Consult with Soil Retention and a local aggregate material supplier where a permeability rate and/or water storage is required. In general, a permeable base material that allows compaction is required for the initial 8 inches. This material generally has no more than 3 % fines passing the No. 200 sieve. In CA an example of this material is Caltrans Class 2 Permeable.

Below the initial aggregate base, a choker course or filter fabric can be used on top of an open graded rock for additional water storage.

For planted applications, special attention to the water retention capacity of the bedding course needs to be considered.

E. Compaction Process

To achieve good compaction, use the type of machine that provides the proper force, amplitude, and frequency.  Continue to add and compact base material until the top of the base is approximately 3.5 in. below the final height of the finished elevation. The remaining space is for the 2.0 in. of sand bedding and the 1.5 in.-thick Drivable Grass® mats.

Establish final height by setting string lines to final elevation. The elevation between the material base and the final elevation should be uniform.

Note: The recommended base surface tolerance should be (+/-) 3/8 in. over a 10 ft. straight edge.

F. Irrigation

Conventional Irrigation:

For conventional irrigation, the plumbing should be buried below the surface of the Drivable Grass® mats within the base course. Muffins can be trimmed as required to allow the spray head to protrude to the surface. This can be done using a masonry bit.

Note: Refer to Section K if installing Drip Tube irrigation.

G. Bedding Installation

For planted applications, a minimum uniform bedding thickness of 2” consisting of a thorough mix of 75% sand and 25% approved fine ground compost shall be used.

The sand should consist of clean, non-plastic that is free from deleterious or foreign matter. The sand shall be sharp and manufactured from crushed rock. Do not use limestone screenings or stone dust. The particles shall conform to the grading requirements given in the table below:

The approved compost material should be finely ground, well screened composted products such as composted manures, mushroom compost or green-waste compost. Material should be able to mix well with sand, able to hold moisture, and provide nutrient

NOTE: It is important to moisten, but do not saturate bedding material prior to installation.

H. Screeding

Spread the 75% sand-25% compost mix uniformly and compact using vibrating plate compactor. Use screed rails/edge restraints and string lines to assure the screeded 75% sand-25% compost mix will allow the top of the Drivable Grass® mats to conform to designed finished elevations.  Allow 1/8 in. to 1/4 in. above specified surface elevations to compensate for minor settlement.

I. Drivable Grass® Mat Installation

Do not drag the Drivable Grass® mats or walk on 75% sand-25% compost mix bedding as this can cause uneven placement.

Install the Drivable Grass® mats in a running bond pattern. Working in one axial direction at a time, securely butt mats up against each other. Trying to install Drivable Grass® in more than one axis at a time could result in a significant alignment problem. Make sure to check the alignment in both directions. Make minor adjustments to Drivable Grass® mats as required to maintain good grid pattern alignment.

The grid inside the Drivable Grass® mats can be cut with a utility knife or chisel to fit site conditions. At terminating edges or curved installations, the mats can also be cut with a masonry blade. Be sure to properly clean the Drivable Grass® mats after cutting with a dry blade by brushing or blowing to avoid staining from fine dust.

Partial mats (minimum of 2 X 2 muffins) should be limited to edges where driving is limited. Make sure to make minor adjustments to fit large pieces leaving no significant gaps between the edge restraint and the mats.  Secure partial mats using 8 in. spikes in a minimum of two locations.

  1. Seat the Drivable Grass® mats into the bedding course using a low-amplitude, 75-90 Hz vibrating plate compactor capable of at least 4,000 lbs. centrifugal compaction force. Use a fabric or pad between the compactor and Drivable Grass® mats to prevent scuffing or chipping
  2. Final surface tolerances should be as follows:
    1. Final surface tolerance of Drivable Grass® mats shall not deviate more than (+/-) 3/8 in. over a 10-foot straight edge.
    2. Surface elevation of the Drivable Grass® mats shall be 1/8 in. to 1/4 in. above adjacent drainage inlets, concrete collars or other type of inlets.
    3. Lippage: No greater than 1/8 in. difference in height between Drivable Grass® mats.

J. Drip Tubing Irrigation

Drip Tubing: For drip irrigation, the tubing should be placed between Drivable Grass® muffins and secured in place with staples. The flow rate, tube and emitter spacing should be placed in accordance with the project plans and specifications.

K. Infill (same material as bedding)

Brush the infill between the muffins of the Drivable Grass® mats. The infill mix should be recessed at least 1/4″ below the mat surface.

NOTE: Estimated Infill Volume = 0.2 Cubic Feet per Mat OR 0.05 Cubic Feet per Square Foot.

L. Grass Infill

NOTE: Grass infill type should be as specified in the project plans.

  1. Seeded Applications:
    • Broadcast approved grass seed evenly over the Drivable Grass® mats.
    • Lightly cover with a seed cover. The seed cover should be light and not contain small particles that mix into the infill and can be sucked up by the lawn mower.
    • Keep seeds moist as they sprout, watering often so germinating seeds never dry out
  1. Hydroseed Applications:
    • Apply approved hydroseed evenly at application rate specified.
  1. Sod Applications:
    • Apply the 75% sand-25% compost mixture to completely cover the Drivable Grass® mats approximately 1/4” ABOVE the mat surface.
    • Place the approved sod and use a lawn roller to push sod firmly against soil beneath.

Avoid significant run on during plant establishment and stay off planted areas until established. Mow grass when it reaches 2-3 inches above the surface. Driving can typically begin after the second mowing.

Drivable Grass grass paver
Photo 1: Finished Drivable Grass® planted infill installation.