Reinforcing weak subgrades to restore Weber Road with MIRAFI H2Rx

Overview

The Tararua District Council in New Zealand identified a deteriorating section of Weber Road requiring intervention due to persistent rutting, surface water ponding, and inadequate drainage. The roadway was founded on soft, compressible subgrade soils dominated by high-moisture silts and clays. These soils exhibited low shear strength and a high susceptibility to settlement, creating ongoing risks to pavement integrity and traffic safety. A geosynthetic solution was required to stabilize the subgrade, manage excess moisture, and improve the long-term performance of the pavement structure.

Challenge

The primary challenge was the poor condition of the subgrade, characterized by high moisture content, low bearing capacity, and a tendency toward differential settlement. These conditions complicated construction activities and increased the likelihood of deformation under traffic loading. Water retention within the subgrade contributed to pumping and progressive softening, accelerating pavement distress.

Solution

MIRAFI^® H2Rx multifunctional woven geotextile was selected to address the combined requirements of subgrade reinforcement and moisture control. Manufactured from high-tenacity polypropylene yarns, the geotextile provides mechanical stabilization, separation, and advanced moisture management. Its high tensile modulus delivers lateral restraint and load distribution, improving bearing capacity and reducing deformation. Integrated wicking fibres actively remove excess pore water, limiting subgrade saturation and preventing pumping and softening beneath the pavement.

Site preparation involved light grading to correct surface irregularities while avoiding heavy equipment that could further disturb the soft soils. The geotextile was installed along the road alignment using light machinery, oriented in the direction of traffic flow. Longitudinal seams were overlapped by 300 to 450 mm, and cross-roll overlaps were staggered to reduce potential weak points. A total of 6,750 m² of MIRAFI H2Rx was installed, creating a uniform, reinforced working platform.

The installed geotextile evenly distributes traffic loads across the moisture-sensitive subgrade while continuously drawing excess water away from the pavement structure. By equalising moisture conditions and limiting subgrade deformation, the solution transformed the roadway into a stable, durable pavement system capable of addressing the original geotechnical challenges and extending service life under ongoing traffic demands.

Images courtesy of Geofabrics. Used with permission.