Geogrid Reinforced Pavement Design for Weak Subgrade | Barnet Vehicle Depot

Barnet Council, working alongside main contractor Willmott Dixon, embarked on the development of the Oakleigh Road South Vehicle Depot, a key infrastructure project designed to support the borough’s waste collection and recycling operations. The facility includes refuse vehicle parking, maintenance buildings, cleaning bays, refuelling stations, and a covered bulking area for efficient waste handling and transfer.

A critical aspect of the project involved upgrading the pavement structure at the site entrance and junction off Oakleigh Road South to accommodate frequent Heavy Goods Vehicle (HGV) traffic. These vehicles impose substantial loads, making pavement durability and long-term performance essential.

However, challenging ground conditions posed a significant risk. The site exhibited a general California Bearing Ratio (CBR) of 3%, with weaker zones dropping to as low as 1%. Such low CBR values indicate poor load-bearing capacity, increasing the likelihood of rutting, deformation, and premature pavement failure. As a result, an effective ground stabilisation and pavement reinforcement solution was required to ensure structural integrity under heavy traffic conditions.

To overcome the weak subgrade conditions and ensure a high-performance pavement structure, a reinforced design was developed based on a conservative subgrade assumption of CBR = 1%. The solution incorporated the Maccaferri MacGrid EG40S geogrid within the unbound aggregate layers to provide advanced soil stabilisation and load distribution.

The pavement design followed the American Association of State Highway and Transportation Officials (AASHTO) method, a globally recognised standard for flexible pavement design. This approach determines the required Structural Number (SN), which defines the total pavement thickness needed to support projected traffic loads over the design life, while accounting for subgrade strength.

By integrating the extruded biaxial MacGrid EG geogrid into the base and subbase layers, the structural performance of the pavement was significantly enhanced. The geogrid improves aggregate interlock and confinement, increasing the effective layer coefficients and reducing stress on the कमजोर subgrade. This results in improved load-bearing capacity, reduced deformation, and extended pavement lifespan.

To accurately model and optimise the design, Maccaferri utilised its proprietary MACREAD 2.0 software. This advanced tool applies a modified AASHTO methodology, incorporating the Layer Coefficient Ratio (LCR) to quantify the structural contribution of geogrid reinforcement. The result was a cost-effective, durable, and sustainable pavement solution tailored for heavy-duty HGV operations.

This project demonstrates how geogrid-reinforced pavement systems can successfully address poor ground conditions, delivering long-term performance benefits for infrastructure projects involving heavy traffic and subgrades.