Geosynthetics Part 1: Geotextiles

Summer 2016

New ICPI Tech Spec provides comprehensive guidance for construction with geosynthetics

Figure 3: PICP geotextile locations

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Geosynthetics Part 1: Geotextiles

Geosynthetics can be grouped into several product categories; geotextiles, geogrids, geomembranes, geonets, geosynthetic clay liners, geopipes, geofoam, geocells and geocomposites. This article examines construction with geotextiles and future articles will cover construction using the other geosynthetics. The articles are excerpted from a soon-to-be released ICPI Tech Spec that provides a comprehensive view of geosynthetic materials, selection, and construction in various segmental concrete pavement assemblies.

Table_1

When placing geotextile avoid wrinkles in the fabric. Follow the overlap recommendations specified in AASHTO M-288 Geotextiles for Highway Applications as noted in Table 1. Make sure the geotextile is placed in full contact with the surrounding soils or aggregates. Voids, hollows or cavities from wrinkles created under or beside the geotextile compromises its intended function.

Figure 1 illustrates a familiar detail, i.e., separating the compacted aggregate base from the soil subgrade with geotextile. This can help maintain consolidation of the base materials over time by preventing intrusion of fines in the bottom and sides. This slows the rate of rutting in the base and on the soil subgrade.

Geotextile placed under the bedding sand next to the curb provides a ‘flashing’ function. This separates the sand from the base and prevents sand loss into joints between the concrete curb and the compacted aggregate base, as they are two structures that can move independently from each other. Table 2 provides guidelines for geotextile selection depending on the soil and fabric functions required.

Figure 2 illustrates geotextile on a concrete base in a crosswalk application. For new sidewalks, crosswalks and streets, 12 in. (300 mm) wide strips of geotextile are recommended over all joints in new concrete bases to prevent loss of bedding sand, as well as over weep holes. New asphalt generally should not require geotextile on it except at curbs, structures and pavement junctions where bedding sand might enter. For existing asphalt and concrete bases, the surface of each should be inspected for cracks, the severity and extent of which determines repairs. If cracks are few and minor (suggesting substantial remaining life in these bases), geotextile should be placed over the cracks to prevent potential future loss of bedding sand. Covering the entire asphalt or concrete surface with a loose-laid sheet of geotextile can present some risk of creating a slip plane for the bedding sand and paving units as a result of repeated vehicular traffic.

Table_2

Figure 3 illustrates a typical application of geotextile in PICP. Its application against the sides of the subbase and against the excavated soil is essential in all PICP projects that do not use full-depth concrete curbs to completely confine open-graded aggregates at the pavement perimeter. The design and selection of geotextiles for PICP is covered in detail in the ICPI manual, Permeable Interlocking Concrete Pavements – Design, Specification, Construction, and Maintenance.

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