Combigrid® Plenty Rd Upgrade- Stage 2

Project Background

Plenty Road connects some of Victoria’s fastest growing regions and suburbs. It is a vital upgrade in Melbourne’s north, along with Yan Yean Road and O’Herns Road, to aid people in getting to places where they need to be sooner and safer.

The Plenty Road Upgrade is occurring in two different stages. The upgrade will provide better access to jobs, schools, shops, and parks. Construction partner delivered the project, with major construction on Stage 1 completed in July 2019 and Stage 2 due to be complete by late 2020.

Stage 2

Stage 2 between Bush Boulevard and Bridge Inn Road, involves:

• widening Plenty Road from 4 to 6 lanes between Bush Boulevard and Riverdale Boulevard

• widening Plenty Road from 2 to 4 lanes between Riverdale Boulevard and Bridge Inn Road

• upgrading 12 major intersections, including Bridge Inn Road, Waterview Drive and Francesca Drive

• improving cycling and walking facilities.

The second stage of the Andrews Labor Government’s $178.6 million upgrade includes an additional lane in each direction to boost capacity and the installation of new safety barriers to keep drivers safe. Major works have commenced on Stage 2.

Problem

DECMIL contacted Global Synthetics for technical advice, as a pavement geosynthetic design solution option was required to address potential unsuitable subgrade locations that failed proof- rolling requirements as per VicRoads specifications.

When constructing road pavements, special consideration needs to be given to the condition of the underlying subgrade. To aid in the stabilisation of soft subgrades which provides a sound working platform and improves the subgrade bearing capacity for the pavement, a geocomposite reinforcement should be used.

A geocomposite reinforcement comprising of a geogrid and non-woven geotextile, will achieve reinforcement by the primary mechanism of the geogrid interlocking and providing lateral confinement with the cover soil aggregate and the non-woven geotextile providing separation, filtration, and lateral drainage preventing the intermixing and movement of fine particles between pavement layers.  A geocomposite reinforcement can further reduce pavement depths plus the added benefit of helping control differential settlement, reducing the risk of cracks and deformations (ruts). Reducing the pavement thickness can lead to significant reductions in time, construction and labour costs to the client.

Solution

After careful review of the unreinforced pavement design and site specific geotechnical testing data, Global Synthetics technical team provided the contractor with a Combigrid®/Secugrid® geosynthetic reinforcement concept design solution. The suggested design provided a significant reduction in overall pavement depth (≥ 20%) as well as accompanying technical advice to address the proof rolling and treatment of expansive soil requirements as per VicRoads specifications.

Results

DECMIL has successfully been able to achieve proof rolling requirements as per VicRoads specifications and improve the pavement construct-ability issues being experienced on site compared to an un-reinforced pavement design. Furthermore, product handling and laying of Combigrid®/Secugrid® on the project site proved to be very quick and easy with no memory recoil issues compared to other available products.

Combigrid® features

• Reinforcement/stabilisation, filtration, separation, and drainage in just one single product

• Immediate interlock with fill material (no construction-related strain)

• Excellent stress strain behaviour (high tensile stiffness)

• High radial stiffness and high cyclic tensile stiffness

• Robust against installation damage and chemical and biological attack

Choosing the right geogrid for your application will depend on a range of factors. For assistance in choosing the right product for your individual project, contact the specialist engineering team at Global Synthetics.