Specifying Gravel Stabilisation Grids SPECIYING THE NIDAGRAVEL® PRODUCT RANGE FOR YOUR PROJECT
When specifying landscaping or construction products for external works, we understand the importance of having confidence in the products you specify. Our range of Nidagravel® gravel stabilisers are tried and tested in almost every application and can be relied upon to provide a long term, stable and permeable gravel surface. The Nidagravel® range of gravel stabilisers includes three different products, these are Nidagravel® 129, 130 & 140. Each product in the range will stabilise gravel effectively and each product is suitable for a variety applications. The area, loading and intended use of your gravel surface will determine the choice of product. All products can be used for small and large projects, both commercial and non-commercial as all products in the range are multi-purpose with a range of benefits dependant on the application.

SUMMARY OF PRODUCT APPLICATIONS
  • Nidagravel® 129 - lightweight use (Pathways)
  • Nidagravel® 130 - medium weight use (Driveways)
  • Nidagravel® 140 - heavy weight use (Car parking & public space)

  • SPECIFYING THE FILL MATERIAL
    In most cases the fill material will be a decorate aggregate, either a chipping or a gravel. For Nidagravel® 129, 130, and 140 we recommend using a hard, angular decorative aggregate with an average / maximum size of 10mm in diameter. This nominal size aggregate can contain smaller sizes, but ideally not larger. There are two main reasons for this fill specification, firstly this size aggregate settles and compacts well into the individual 49mm diameter hexagonal cells of the honeycomb sheets providing a solid, stable platform. Secondly, the stabilisation sheets are designed to be hidden and this size of aggregate allows for a 10 - 20mm surface layer of aggregate to cover the sheets making them invisible. The finished surface dressing also allows for any torsion forces applied to the surface, ensuring optimum performance and lifespan of the stabilisers.

    SPECIFYING THE SUB-BASE MATERIAL
    Sub-base specification in accordance with BS7533 is recommended for the installation of Nidagravel® products for permeable and non-permeable surfaces. An assessment of the sub-grade should also be made and the surface of the sub-grade material should be prepared according to the Highway Agency's Specification for Highways Works. Nidagravel® products do not replace any part of the sub-base build up and are designed to stabilise the gravel surface only. The honeycomb cell structure of Nidagravel® 129, 130, 140 reinforces the gravel infill and transfers vertical loads from the surface, distributing them over a wider area. Nidagravel® products have very high compressive strengths when filled, from 200 to 300 tonnes per sqm depending on the product. These high compressive strength allows the products to be specified for commercial and industrial use or applications where heavy axle weights are applied to the surface. It is important for specifiers to ensure the sub-base thickness is designed to meet the hydraulic and loading factors of the application. Where Nidagravel® products are to be used as a full infiltration, part infiltration or zero infiltration layer to a Sustainable Urban Drainage System (SuDS) then the guidelines for permeable sub-bases should be applied. The typical sub-base build up for a residential driveway in the UK is a layer of membrane over the sub-grade to act as a ground stabiliser and separation layer, 150mm thick layer of Type 1 MOT 40mm down, which is laid down in two 75mm thick layers to achieve maximum compaction, the surface of the sub-base can then be blinded with a 10 - 15mm layer of sharp or grit sand and compacted. The sub-base of the ready for the Nidagravel® stabilisers to be installed.

    SPECIFYING THE INSTALLATION
    All Nidagravel® stabilisers are designed to be laid on top of the appropriate sub-base for the application and loading. A 10mm - 15mm layer of sharp or grit sand should be used to blind the surface of the sub-base and provide a thin bedding layer for the sheets. Nidagravel® 129, 130 and 140 honeycomb gravel stabilisers have an overlap of membrane along one short edge and one long edge. Once the first sheet is laid these overlaps of membrane are folded out and the next sheet is placed on top and butted up to the previous sheet. No mechanical fixings are required as the weight of the gravel fill is more than sufficient to hold the sheets in place. We recommend laying full sheets across the flow of traffic in a stretcher bond pattern to stagger the joints, but where the site does not permit or it is not economical to do so, other layouts can be used without detrimental effect. Where possible full sheet sizes should always be used in high use areas, such the entry to a driveway. Off cuts can be utilised, to minimise wastage on site, but these should be kept to a reasonable minimum size and be used towards the edge of low use areas. The honeycomb sheets can be cut to fit any shape required including curves and acute angles. It is best to cut Nidagravel® gravel grids using an electric angle grinder or petrol cut off saw for a clean cut. Standard cutting discs can be used including diamond grit masonry discs. Sheets can also be cut with a fine toothed handsaw. It is important to note that Nidagravel® achieves its full strength when filled and no mobile loads should be moved onto the sheets until filled.

    SPECIFYING THE GRAVEL FILL & FILLING THE SHEETS
    We recommend using any decorative aggregate with an average size of 10mm to fill Nidagravel® 129, 130 and 140 gravel grids. A single size 10mm gravel can be specified or a graded decorative aggregate with a range of 4mm - 12mm in size. There are several reasons for this specification, firstly this size of gravel fills the 49mm diameter honeycombs cells perfectly and compacts well with minimal voids. The compacted gravel within the honeycomb cells gives the Nidagravel® stabilizers their full load capacity, which is 200 to 300 tonnes per sqm depending on the product used. Any 10mm decorative aggregate that is currently supplied in the UK either in bulk bags or loose loads can be used to fill Nidagravel® grids. It is generally acknowledge that the characteristics of more angular gravels or decorative chippings can bed down or compact a little better than more rounded gravels. Due to their shape, the individual pieces of angular aggregate, naturally interlock well, but a rounded gravel or pea shingle will also effectively stabilised. The use of a harder stone or gravel that is flint based rather a calciferous stone ensures the longevity of the gravel fill. Nidagravel® gravel grids are designed to be an invisible gravel stabiliser and to achieve this, during installation, the sheets should be overfilled by approx 20mm of gravel. This can only be achieved by using a gravel with an average size of 10mm. Approximately 4 - 6 weeks after installation the gravel overfill will have naturally settled into the honeycomb cells and have been compacted by vehicle and pedestrian traffic to leave approx 10mm - 15mm surface layer of gravel. This settlement / compaction process can be speeded up by compacted the gravel overfill with a plate compactor or wake plate at the end of the installation.

    SPECIFYING THE MAINTENANCE ROUTINE
    This is a simple area to specify as the product range requires very little maintenance after installation. We would recommend that in addition to standard maintenance of external surfaces that a 6 monthly inspection of the surface is carried out to ensure that the honeycomb cells of Nidagravel® 129, 130 and 140 are covered with a 10 - 20mm layer of gravel. This simple visual inspection is quick to complete and where necessary more gravel can be added and levelled as required to maintain the surface layer.