Unpaved Roads Reinforcement Biaxial Polyfabrics Gravel Geogrid

The benefits of geogrids in unpaved low-volume roads have been shown in numerous

laboratory and full-scale experiments (e.g., Haas et al., 1988; Webster, 1993; Collin et al.,

1996; Fannin and Sigurdsson, 1996; Knapton and Austin, 1996; Gabr et al., 2001; and, Leng

and Gabr, 2002). Some experimental programs investigated the performance of different

geogrids (extruded, woven or welded) and the results showed that the stiffer geogrids

performed better (Webster, 1993; Collin et al., 1996). These experiments served as a basis

for the development of the empirical design methods for geogrid-reinforced unpaved low-

volume roads.

Historically the geogrids were introduced to the market in the early 1980s and by that time

geotextiles were used at the base-subgrade interface for separation, filtration and some

reinforcement. As a result, the first empirical design procedures of Barenberg et al. (1975)

and Steward et al. (1977) were developed for geotextiles-reinforced unpaved roads using

solutions based on the limit equilibrium bearing capacity theory. The solution of Steward et

al. (1977) was modified by Tingle and Webster (2003) for geogrid reinforcement and the

proposed modification was adopted in the COE method for design of geotextile- and geogrid-

reinforced unpaved roads (USCOE, 2003). This approach is described in Section 6-1.

Utilizing previous research, Giroud and Han (2004) developed a theoretically based and

experimentally calibrated design method for geogrid-reinforced unpaved roads that reflects

the improvements due to the geogrid-aggregate interlock. The method can also be utilized

for analysis of unreinforced and geogrid-reinforced unpaved roads, or temporary platforms.

This approach will be presented in Section 6-2.

Benefits:

·         Reduces amount of aggregate needed= construction cost savings.

·         Reduces soil excavation and backfilling= construction cost savings.

·         Minimizes differential settlement and prevents upward movement of the subgrade = higher structural performance.

·         Improves overall structural life= maintenance cost savings.