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Thrace-LINQ TECH NOTE #3
INSTALLATION GUIDELINES FOR ROADS AND OTHER HORIZONTAL SURFACES
The success of Thrace-LINQ geosynthetics in roadway applications requires proper installation. Installation techniques are simple and provide assurance that the geotextile will perform as intended. Good, well-graded, granular, road base gravel should always be used. Engineer observation of all construction activities is also recommended to assist the contractor.
- If moderate site conditions exist, i.e., CBR greater than 1, the site should be cleared, grubbed, and over-excavated to design grade.
- During stripping operations, care should be taken not to disturb the subgrade. This may require the use of lightweight dozers or graders for low strength soils or saturated non-cohesive and low-cohesive soils. For extremely soft ground, such as peat areas, consideration should be given to not excavate the surface materials such that advantage can be taken of the root mat, if it exists. In this case, all vegetation should be cut off square at the ground surface. Roots that extend beneath the ground surface should not be removed. Trees and stumps could be cut off at the ground surface and sawdust or sand placed over those areas to protect the geotextile. Remember, the subgrade preparation must correspond to the survivability of the geotextile.
- Once the subgrade along a particular segment of the surface has been prepared, the geotextile should be rolled in line with the placement of the new aggregate. The geotextile should not be dragged across the subgrade. The entire fabric rolls should be placed and rolled out as smoothly as possible. Wrinkles and folds in the geotextile should be removed by stretching and staking as required.
- Parallel rolls of the geotextile should be overlapped or sewn. The following table is for your consideration:
|Recommended Minimum Overlap Requirements|
Greater than 1
0.5 - 1
3 Feet or Sewn
Less than 0.5
All Roll Ends
3 Feet or Sewn
- For curves, the geotextile should be folded or cut and overlapped in the direction of the turn (previous geotextile on top).
- When geotextile intersects on existing pavement area, the geotextile should extend to the edge of the old system. For widening or intersecting existing roads where geotextile has been used, consideration should be given to anchoring the fabric at the roadway edge. Ideally, the edge of the roadway should be excavated down to the existing geotextile and the existing geotextile sewn to the new geotextile. Overlaps, staples and pins can also be utilized.
- Before covering, the condition of the geotextile should be observed by a qualified engineer to determine that no holes, rips, tears, etc....occur in the geotextile. If any defects are observed, the section of the fabric containing the defect should be repaired by placing a new layer of geotextile extending beyond the defect in all directions. The overlap should be at least 3 feet in all directions.
- The aggregate should be end-dumped on previously placed aggregate. For very soft subgrades, pile heights should be limited to prevent construction-induced road failure.
- The first lift of aggregate should be graded down from the previously placed fill to 12 inches, or to the design thickness if less than 12 inches prior to compaction. At no time should equipment be allowed on the road with less than 8 inches (6 inches for CBR greater than or equal to 2) of compacted aggregate over the fabric. For extremely soft soils, lightweight construction vehicles will likely be required for access on the first lift. Construction vehicles should be limited in size and weight such that rutting in the initial lift is no greater than 3 inches.
- The first lift of sub-base aggregate should first be compacted by tracking with the dozer and then compacted with a smooth non-vibrating drum roller to obtain a minimum compacted density. For very soft soils, design density should not be anticipated for the first lift and as such, compaction requirements should be reduced. A recommendation would be to require a compaction level of 5% less than the required specification density.
- Construction should be performed parallel to the road alignment. Turning should not be permitted on the first lift of sub-base aggregate. Turn-outs may be constructed at the road edge to facilitate construction.
- If the geotextile is used in the reinforcing function, pretensioning of the fabric should be considered. Four passes over the first lift in each area of the site is recommended. Alternatively, once the design aggregate has been placed, the roadway could be used for a time prior to paving such that pre-stressing the geotextile in key areas will be obtained.
- Any ruts that form during construction should be filled in with good granular material to maintain adequate cover over the geotextile. In no case should ruts be bladed down. This decreases the amount of aggregate cover over the geotextile.
- All remaining lifts of sub-base aggregate should be placed in loose lifts not exceeding 9 inches in thickness and compacted to the appropriate specification density.