Project Summary/Scope:

A contractor was building an access road over historic marsh land when the crew encountered a high water table and 10-15 ft. of soft soils. The original solution to stabilize the subgrade used a non-woven geotextile and 2-3 ft of rock, however, the roads quickly rutted and became unserviceable for their heavy dump trucks. Time was of the essence since the access road was critical for transporting a necessary drill rig.

The contractor decided to try a solution using a multi-axial geogrid. The geogrid design not only reduced the required aggregate thickness but also allowed the use of 3/4” aggregate instead of the expensive ballast rock needed with geotextile. The geogrid has apertures (openings) that allow aggregate to interlock. Interlock is the key that prevents rutting since it confines the granular particles to keep them from spreading laterally when loads are applied down from above. Ultimately, this solution cut construction time in half while keeping costs similar to the original budget.

Alternate Technologies: A geotextile was originally used to stabilize the soft soils but the access road quickly failed under repeated truck traffic.

Performance Monitoring:  N/A

Cost Information:  The contractor recovered valuable time after the road became unserviceable with the original geotextile solution.

Case History Author/Submitter:  Alec Anderson, P.E.; Tensar Regional Manager Pacific Northwest; Aanderson@tensarcorp.com

Project Technical Paper: N/A

Date Case History Prepared:  Dec. 2021

Case History Prepared By: Katie Phillips