Benefits of Using Geotextile Between Subgrade Soil and Base Course Aggregate in Low-Volume Roads in Virginia

About the report:

Geosynthetics have increasingly been used since the 1960s in pavement structures to provide reinforcement; to serve as a permeable separator to prevent mixing of subgrade with subbase or base course materials; and to provide drainage.  A reliable method of quantifying these benefits is needed to justify the more widespread use of these materials. 

The purpose of this study was to quantify the benefit of using a geotextile as a separator in low-volume roadways such as secondary and subdivision streets.  A field trial was conducted on a section of Virginia Route 743 near the Charlottesville-Albemarle Airport in Albemarle County to achieve this objective.  A geotextile was placed between the aggregate base and subgrade in one lane of the section to prevent failure attributable to intermixing, and the adjacent lane was left unmodified as a control.  In addition to the field trial, a small-scale accelerated loading laboratory test was conducted to quantify the benefit of using geotextile as a separator for a range of pavement design variables, including variations in soil strength, traffic volume, and aggregate properties. 

A statistical analysis of data gathered by a falling weight deflectometer during construction and after 8 months of traffic showed the lane with geotextile to have a slightly higher structural capacity.  As severe intermixing and base failure in the control section were not expected during the 8-month period because of the low volume of traffic and a dry season, the benefit may have been attributable to a reinforcing effect. 

Although the size of the apparatus and the boundary condition may have prevented the most accurate quantification of the benefit, the laboratory testing further demonstrated the benefit.  Most laboratory samples with geotextile had less deformation than the control sample.  Intermixing of soil and aggregate was not observed when very densely graded base aggregate was used.  When a more open-graded aggregate was used, the geotextile reduced the amount of fines migration into the aggregate layer; however, the fouled aggregate did not appear to have lost significant structural stiffness.  Therefore, the separator benefit of geotextile in the laboratory testing was also apparently attributable to a reinforcing effect. 

The use of geotextile materials appears to have great potential to extend the service life of pavements on the secondary road system, offering significant cost savings to VDOT.  It is recommended that this section of road be periodically evaluated to quantify this potential increased service and that more test sections on subdivision streets with a weaker subgrade condition or full-scale accelerated testing be conducted for a reliable quantification of the benefit.

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