1. Search

Grassgrid

General principles

Installation design for Grassgrid Ground Reinforcement system varies according to the following factors:

• Application type
• Anticipated loadings (if trafficked)
• Nature of existing sub-grade
• Degree of gradient (if relevant to application type)

Application types

Vehicular traffic - including:

• Pedestrians
• Private cars
• Light commercial vehicles (including light aircraft)

Gradients - including:

• Cuttings/slopes
• Motorway embankments
• Spillways (for flood control works)

Water courses - including:

• River bed reinforcement
• Restraining bank construction
• Existing bank stabilisation

Laying design

The recommended laying design of Grassgrid units is influenced by the specific application type and circumstances:

Vehicular traffic

Half-bonded – preferably in a restrained area.

Edge restraints
Edge restraints are recommended wherever possible, especially for heavier loading applications.

Sub-grade
Stability of sub-grade needs to be assessed as this will affect sub-base requirement.

Sub-base

If sub-grade is stable:

• No sub-base required (for lighter loadings only).
  If sub-grade is not stable:
• Material: granular sub-base type 1.
• Compacted depth: for light traffic applications: 100 mm min,
  for heavier traffic applications: 150 mm min.

Laying course

• Material: sharp sand and (if available) loam (1:1 mix).
• Compacted depth: 20 mm.

Gradients

Edge restraints are recommended wherever possible, especially for heavier loading applications.

With edge restraint:
Half-bonded laid up slope, starting from an edge restraint along foot of gradient.

Sub-grade
Condition of the sub-grade needs to be assessed as this will affect sub-base requirement. It should be stable, compact and rock-free.

Sub-base

If sub-grade is stable:

• No sub-base required. Grassgrid may be laid directly onto sub-grade.

Laying course

Required if laying on sub-base, otherwise optional:

• Material: sharp sand and (if available) loam (1:1 mix).
• Compacted depth: 20 mm.

Without edge restraint:

Staggered vertical jointing plus every 2nd or 3rd row staked with 500 mm wood or metal pins to ensure stability.

Edge restraints are required for all gradients unless shore restraint pins are used (see under Laying design).

Water courses

For river/canal banks:

Staggered vertical jointing plus every 2nd or 3rd row staked with 500 mm wood or metal pins to ensure stability.

Edge restraints

Not normally required.

Sub-grade

Condition of the sub-grade needs to be assessed with extra care. It must be stable before laying.

Sub-base

Not normally required.

Laying course

Material: geotextile membrane (eg. Terram).

Perforations: (to allow root penetration/stem reinforcement during growth of reeds and aquatic plants): 0.2-0.4 mm (200-400 microns).

Protects sub-soil and prevents erosion by waterflow.

Grassgrid ground reinforcement

Sub-base:

• If ground is unstable, prepare 100 mm minimum sub-base of granular type 1 material.
• If heavier traffic is envisaged, sub-base should be 150 mm minimum.

Bedding/laying

• Prepare 20 mm compacted laying course of sharp sand and (if available) loam: mix 50:50.
• Screed lightly and lay units in rows or half-bonded (preferably in restrained area).
• Tamp down with paviour’s maul.
• Fill cavities with good quality soil to within 30 mm of surface: sow with grass seed* and top up cavities with soil to level of surface.

*recommended: British Seed Houses Mixture A7.