A VETERAN OWNED BUSINESS
To prevent damage to the Geo-Grid, the site should be free of sharp objects, cleared of all debris, stumps, plant growth, top soil, stones, and other materials. Place the rolls of Geogrid in position, cut the roll bands and manually unroll the material over the prepared surface. In some instances where very low subgrades are present, it may be beneficial to leave some vegetation, top soil, and fine root mats in place. Proper equipment should be used to smooth and compact the subgrade to the specified requirements. Check with the engineer for subgrade compaction requirements. The engineer shall verify that the subgrade and elevations are ready for Geogrid installation. For moderately competent soils (CBR > 2), it may be prudent to lightly proof roll the subgrade to locate unsuitable materials. When possible, backdrag to smooth out any ruts. Smooth grade and compact the soils using appropriate compaction equipment. Swampland, peat, muskeg or marshes may be difficult to smooth grade and/or compact. In these situations, create a surface that is as uniformly smooth as possible. Grade or crown the surface for positive drainage away from the construction zone.
Geo-Grid rolls are commonly rolled parallel with the roadway system. However, where conditions include very soft subgrades, it may be beneficial to lay out Geo-Grid rolls perpendicular to the road. The rolls should be overlapped 1 to 3 ft side-to-side and end-to-end with the overlapping in the same direction as the aggregate placement. To accommodate curved sections, Geo-Grid should be cut and overlapped. Cutting of Geo-Grid may be done with sharp shears and other handheld cutting devices. It is mandatory that the proper safety equipment be used while cutting and installing Geo-Grid. The Geo-Grid may also be cut to accommodate other immovable protrusions such as manhole covers. The Geo-Grid should begin to be rolled out from an area easily accessible to construction equipment. For very soft subgrades, the layout should begin on firm soils on the perimeter of the project. This will act as an anchor point from which you can roll the Geo-Grid onto softer sections. Frequently check to make sure your alignment is being maintained throughout your Geo-Grid installation process
While unrolling Geo-Grid, maintain alignment and pull it taut to remove any slack and wrinkles. Do not roll out too much Geo-Grid at once. Start with about 40 ft and continue unrolling as aggregate is spread. Be sure to anchor the beginning of each roll at the center and edges before fully unrolling the material. To hold Geo-Grid in place prior to aggregate placement, soil, rocks, or other weights may be used to hold the Geo-Grid edges and overlaps in place. Small shovel piles of aggregate are commonly used along overlaps, edges, and corners. If allowed, anchor pins or sod staples may also be used.
The aggregate is placed and spread over Geo-Grid using normal construction methods and equipment. For soft subgrade conditions, low ground pressure models are recommended. The aggregate is normally back dumped then spread out over the Geo-Grid. Tracked bulldozers are commonly used for spreading of the aggregate. A test section should be evaluated to determine the possible damage from direct vehicle contact. If acceptable, aggregate may be dumped as the vehicle advances. Sudden starts, stops, and turns should be avoided when operating equipment directly over Geo-Grid. Tracked construction equipment should not be operated directly on the Geo-Grid and turning or pivoting of tracked equipment over installed aggregate should be kept to a minimum to prevent tracks from displacing the aggregate and damaging the Geo-Grid. Lift thicknesses are generally not less than 6 inches. The initial lift may be as thick as necessary to prevent rutting or failure of the subgrade soils. During spreading, the bulldozer blade should raise gradually as each lift is spread over the Geo-Grid. Take caution not to catch the bulldozer blade or any other equipment on the Geo-Grid. The shoving action from bulldozers or other aggregate spreading equipment may cause waves in the Geo-Grid layout ahead of the fill. This can be minimized by unrolling the Geo-Grid a little at a time. Once sufficient aggregate is in place on the Geo-Grid, unroll the next section.
AGGREGATE FILL CONSIDERATIONS The preferred gradation is well-graded crushed aggregate fill with maximum particle size of 1½ in. and less than 10% fines (passing #200 sieve). The gradations listed in Table 2 (below) provide good stability and low moisture susceptibility. Other granular fill may be acceptable depending on project conditions – this determination should be made by the engineer of record for the project. As a part of this determination, a filter analysis should be performed to determine whether a geotextile is required to maintain separation between the aggregate fill and the subgrade
Standard compaction methods may be used unless the soils are very soft. In these cases, static instead of vibratory compaction is recommended. Compaction is then achieved using a light roller. Keeping the moisture content of the fill material will make compaction more efficient. Water spray is most effective with sand fill. For construction over very soft soils, compaction requirements are normally reduced for the initial lift as the primary intent of the initial lift is to achieve a suitable working surface. If rutting or severe pumping occurs under truck or dozer traffic, fill should be added immediately to strengthen the section. Compact aggregate fill to project specifications, after it has been graded smooth and before it is subject to accumulated traffic. Inadequate compaction will result in surface rutting under wheel loads. This rutting reduces the total effective thickness of the fill and increases stress on the subgrade. In extremely wet conditions, it may be necessary to cease operations to allow pore pressures to dissipate from the subgrade and reduce moisture content. Weak areas found during final compaction commonly indicate inadequate aggregate thicknesses at those locations.
At sub-freezing temperatures, Geo-Grid is less impact resistant and can be fractured with dynamic force (i.e., striking with a hammer). Other aspects of dynamic loading associated with very cold temperatures should be avoided. For example, direct trafficking by rubber-tired equipment atop Geo-Grid is permissible when the subgrade is competent. However, it’s not advisable at very cold temperatures.
If Geo-Grid is damaged during or after installation, it can be repaired by patching the area. To repair the damaged Geo-Grid section, first excavate the fill from the damaged area extending 3 feet in all directions of the damage. Place a Geo-Grid patch over the damage, extending at least 3 feet in all directions, and replace the excavated material and re-compact.