Advantages of Creating Uniform Subgrade Elevations

by Joe Heintz, P.E., on August 20, 2020

Retail Center_Uniform SubgradeMany private sites are designed with both a thick, heavy-duty pavement and a thinner, light-duty pavement to account for variability in traffic. Often times, these varying pavement thicknesses are directly adjacent to one another, causing design, construction and maintenance problems. The most significant being that water entering the pavement tends to accumulate in the “bathtub” created by the thicker heavy duty section (see Design Scenario 1 below.) The subgrade strength decreases and the base becomes saturated which results in a weaker pavement in the area where the greatest strength is required.

Advantages of Uniform Subgrade Elevations

There are many advantages to creating a uniform subgrade elevation for adjacent heavy and light duty pavement sections:

  • The potential for migration of water into low lying areas is avoided, thus the pavement strength is maintained.
  • Elimination of water trapped below the heavy-duty section reduces its freeze-thaw susceptibility.
  • Less complexity in construction operations due to variable material thicknesses, including staking, grading and paving, minimizing construction errors and ensuring accurate as-built pavement sections.
  • The site can be graded to one level, resulting in less excavation, disposal and new pavement materials, resulting in cost savings and shorter construction time.

TriAx Geogrid for Uniform Subgrade Elevations

TriAx Geogrid technology from Tensar can be used to create a scenario whereby the heavy and light duty sections are the same thickness. Consider the two sets of designs illustrated below and make note of the highlighted reductions in pavement and aggregate sections resulting from the integration of TriAx Geogrid. The enhanced performance of pavements stabilized with TriAx derives from the positive interaction between TriAx and aggregate. Penetration of the coarser particles through the openings of TriAx results in “mechanical interlock”. This increases the stiffness of the base course layer and prevents lateral spreading of the aggregate during traffic loading, allowing thinner pavements stabilized with TriAx to perform structurally better. 

Uniform Subgrades

In Scenario 2, the stabilized heavy and light duty pavement sections exceed the traffic capacity of their unstabilized counterparts in Scenario 1. The difference however, is that the stabilized heavy and light duty pavements both have the same thickness and underlying subgrade elevation.

When used in pavement applications (i.e. reasonably firm subgrade conditions), TriAx Geogrid provides the following benefits:

  • Increased speed of construction: The installation process for Tensar TriAx is extremely straightforward. Using less aggregate and asphalt with TriAx leads to quicker installation when compared to placing additional conventional materials.
  • Increased design life and reduced maintenance for a given pavement section
  • Reduced pavement thickness required for a given required traffic level, reducing total project cost

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