The interplay between the base course, the grid and the aggregate is key to achieving the desired reinforcement properties – so proper installation is a must.
This article provides guidance on how to install geogrids for pavement reinforcement, focusing on our E’GRIDⓇ and E’GRIDⓇ GT products which are typically used in pavement applications.
Note that this information is provided as a guide only. Every project is unique, so always consult the Polyfabrics team or a certified engineer for site-specific installation instructions.
How to install geogrid
1. Subgrade Preparation
E’GRIDⓇ and E’GRIDⓇ GT can be installed directly on top of grass and low vegetation, provided there are no large or woody plants or bushes in the area. Remove any large rocks or similar obstacles and ensure voids, depressions or wheel ruts are filled or levelled off to provide a smooth surface.
On very soft ground, it is advisable to cut vegetation flush with the ground to leave the root zone and soil crust undisturbed.
2. Product Installation
To install the geogrid, simply roll it out and allow it to follow the natural contours of the ground. Generally, the direction of laying and vertical spacing of multiple layers will be specified in the design documents. E’GRIDⓇ can be placed on the subgrade, either parallel to a road centerline or at right angles. In the majority of cases, only one layer of geogrid is required between the compacted fill and the ground below. If multiple layers are required and spacing is not specified they should be evenly spaced through the thickness of fill with spacing not exceeding 500mm.
Once in place, the geogrid should be tensioned by hand to remove any slack and to ensure that any mechanical joints are taught. Small deposits of fill material may need to be placed on top of the grid to hold it in position until the main fill placement commences.
Note that no construction traffic should travel directly on the geogrid before fill placement.
3. Direction of Placement, Continuity & Cutting to Size
Over very soft ground, the geotextile must be facing down. To ensure product continuity, simply overlap adjacent layers. Roll edges and ends should have a minimum overlap of 300mm. Over soft or uneven soils these overlaps may need to be increased up to as much as 900mm.
Typically, as the ground strength reduces below CBR 4, the overlap should increase, and overlaps should be shingled in the direction of fill placement.
Care should be taken to ensure that the overlaps are maintained during fill placement and don’t move out of place. Cable ties or steel pins at 1m spacing can help to hold overlaps in place.
E’GRIDⓇ and E’GRIDⓇ GT may be cut to length or width using either snips or a disc cutter.
4. Placing the Cover Fill
Fill material should be placed at either the starting edge of the geogrid or on top of the already placed fill, before being spread to the required depth using a tracked machine.
A minimum fill layer thickness over the geogrid of 150mm is recommended before any trafficking or compaction. During spreading, the bulldozer blade should be angled back to lift fill rather than push it.
5. Selecting the Right Fill & Compaction
A selection of fill types can be used with E’GRIDⓇ and E’GRIDⓇ GT. Ideally, the use of a graded aggregate is recommended. Compaction of the sub-base material should follow the appropriate clause of the project specification.
Advice on geogrid installation
For further advice on the best methods to install geogrid for pavement reinforcement and a wide range of other applications, get in touch with the technical team at Polyfabrics.
Note: It is the responsibility of the specifier and purchaser to ensure that product specifications used for design and procurement purposes are current and consistent with the products used.