Geosynthetic Installation Damage Under Two Different Backfill Conditions

Six different geotextiles and one geogrid were placed on an angular, poorly graded gravel, backfilled with the same type of gravel,compacted in a standardized manner, and then exhumed within the same day. A visual damage assessment indicated that the exhumed geotextiles had 60 to 108 holes per square meter and the geogrids had approximately 4 damaged ribs per square meter. A large number of strength tests were performed on the exhumed samples and compared to the original (as-received) strengths to obtain an average percent retained strength. The results for the geotextiles were from 30% to 58% strength retained while the geogrid resulted in a 71% strength retained. At a second site the entire study was repeated with new materials but now the soil was a poorly graded sand both beneath and above the geosynthetics. The same types of geotextiles and geogrids as with the first site were used in these tests. Here the results were very different, with no holes or damaged ribs, and average geotextile strengths retained from 72% to 96%. The geogrid had its full strength retained. The data results in quantifiable values for installation damage partial factors-of-safety (the inverse of the strength retained), as well as guidance on the type of backfill soil to use with polymeric reinforcement. Clearly, angular gravel can be damaging to both geotextiles and geogrids and should only be used with considerable caution or with the addition of protection materials.