By: William G. Handlos, P.E.

Research shows that GEOTERRA® and GEOTERRA® GTO structural mats provide a ground-surface reinforcement layer to support heavy loads over soft subgrades. More cost-effective than other reinforcement mat systems, the GEOTERRA mats can be used for temporary or permanent applications and are reusable. Offering high crush and flexural strength, the GEOTERRA mats have demonstrated the ability to handle the forces from some of the heaviest wheeled and tracked vehicles under severe conditions.

Scope of Test:

The University of Kansas Geotechnical Laboratory tested the performance of the GEOTERRA and GEOTERRA mat systems over weak to intermediate subgrades with CBR values ranging from 1% to 4%. They conducted a total of 12 tests to identify threshold and limit conditions, create a data-set for modeling, and determine the equivalent crushed aggregate base.

Testing Procedure:

Test sections were subjected to 40 kN (9 kip) cyclic loading on a 300 mm (12 in) diameter plate. Earth pressure cells were placed over of the subgrade to measure vertical interface stress distribution. Loading plate displacements were measured by the displacement transducer inside the actuator.

Test Observations:

The following conclusions were determined for the GEOTERRA and GEOTERRA GTO Structural Mat Systems:

• The GEOTERRA mats provide additional support for weak to intermediate subgrade subjected to cyclic loadings by reducing permanent deformations and rate of increase in the permanent deformation of the subgrade.
• The GEOTERRA GTO mats was most effective in cases of larger permanent displacement.
• The vertical interface stresses between the mat and the subgrade close to the center of the loading plate decreased with an increase of loading cycles. This result is different from that for the aggregate base over the subgrade, in which the vertical interface stresses close to the center increased with the number of loading cycles.
• Both GEOTERRA mat systems performed similarly to the 12-inch (300 mm) crushed aggregate base over 2% and 4% CBR subgrades.

Test Conclusions:

• Both GEOTERRA and GEOTERRA GTO mats decreased interface stresses at the load point, which reduces soil movement and ultimately leads to a significant reduction in rutting.
• Although subjected to rigorous point load testing, the GEOTERRA mats received no significant damage.
• The testing data proved that the GEOTERRA mat system performed similarly to 12 inches (300 mm) of crushed aggregate base in controlling permanent deformations over 2% and 4% CBR subgrades, with the GEOTERRA GTO mat system performing similarly, but slightly better.

Modular polyethylene construction access mats are lightweight, easy to place without the need for heavy construction equipment, and particularly useful when speed of placement and removal are a factor or when space is at a premium.

To get more information about GEOTERRA mats, go to www.prestogeo.com/products/construction-mats/geoterra-construction-mats/.