Shallow Dig, Strong Result. Pavement Rehabilitation with Combigrid®

The Project

In early 2026, Parkes Street in Wellington required pavement rehabilitation due to significant subgrade instability and moisture-related pavement distress. The project involved reconstructing the pavement while maintaining road access and minimising risks to existing underground services.

An initial geotechnical option put forward was to excavate and replace approximately 800mm of pavement material. However, this approach was considered too costly and impractical for an urban street. In addition, shallow watermain spindles located only 350–500mm below the surface created a high risk of service damage during deep excavation.

The team sought a smarter alternative, turning to geosynthetic reinforcement as a more practical way forward. With advice from Global Synthetics, a more cost-effective reinforced pavement approach using Naue Combigrid® Geocomposite was adopted.

The Challenge

• Excessive pavement deflection caused by an underground water stream

• Moisture-affected subgrade conditions

• Shallow buried water infrastructure limiting excavation depth

• Need to maintain access during construction

• High cost associated with full-depth pavement replacement

The Solution

The adopted pavement rehabilitation methodology included:

• Excavation of approximately 300 mm of existing pavement

• Removal of unsuitable material

• Installation of Combigrid® geofabric reinforcement

• Placement of two 150mm layers of DGB20 pavement material

• Compaction and proof rolling

This approach using Combigrid® reinforcement allowed the pavement to be constructed with significantly reduced excavation depths while improving stability over weak and saturated ground conditions.

The Result

The reinforced pavement delivered strong results under challenging conditions. The pavement achieved acceptable performance prior to sealing, with the Combigrid® effectively controlling deflection and improving subgrade stability.

The full-width installation capability of the geofabric simplified construction activities and improved productivity. Once crews became familiar with the system, approximately 100 metres of pavement could be constructed per day. The reinforced pavement also improved trafficability during construction, avoiding the need for extensive side tracks or short staged construction lengths.

Most significantly, the reinforced design eliminated the need for the originally considered 800mm reconstruction, substantially reducing excavation volumes and imported material requirements.

The Parkes Street project demonstrates that geosynthetic reinforcement can offer a practical, economical option for pavement rehabilitation. Need help with your next road construction project? Contact Global Synthetics today.