Hawkridge Heights, Tauranga – MagnumStone™ Gravity Wall

Nestled into the foothills of the Tauranga suburb of Bethlehem, Hawkridge Heights is a residential area currently being developed to add more housing. Accessed off Carmichael Road, it overlooks a branch of the Tauranga Wetlands. 31 new lots are to be created on the current sloping land, with driveways and right of ways coming off Mayfield Lane. Bordering the wetlands and the toe of the newly developed residential slope, Mayfield Lane is being extended into a cul-de-sac to help gain more usable land and create the new accessways to each lot.

To lift Mayfield Lane clear of the wetland, Classic Developments required a retaining wall solution that would support the cul-de-sac once it is placed between the flood plain and the base of the 20-25m moderate to steep sloped embankment. A cantilevered timber pole design had been considered, but MagnumStone’s versatility, ease of installation and aesthetics gave greater value to the estate.

DESIGN

Retained to a maximum height of 4.8m, this 77m tiered, curved gravity wall with extenders will run the length of the new extension and create the tight turning circle at the end of the cul-de-sac. As the wall sits on a 22° toe slope at its base, the retained height will also include 1.2m of embedment.

With MagnumStone providing a 100 year design life, the wall will take traffic loading up to a 12kPa widespread distributed load. A combination of large and small extenders will be used, ranging from a length of 1.22m to 2.44m, depending on the retained height of the wall.

MagnumStone’s standard 87.6° batter ensures maximum land use, allowing the pavement and an upper drainage area to be installed right to the edge of the wall. A safety railing will also be placed along the top of the MagnumStone wall, with a further wooden protection rail being added into the drainage area, set just within the wall.

INSTALLATION

To provide a level platform for the wall’s construction, a 200mm thick levelling pad of GAP40 was placed on the compacted subgrade. The design of the wall incorporated site won material being compacted around the extenders, with drainage material being placed within MagnumStone’s hollow core. The tapered end of the cul-de-sac curve was embedded into the slope. Because consistent rows of 2.44mm extensions could not be placed within the tight curve, the combination of large and small extenders were placed first at every second block, with single small extenders placed in the gaps between them. The top layer of MagnumStone was filled with concrete, with the safety rail inset into the concrete within the MagnumStone blocks’ hollow core, giving developers and future residents safe and supported access to their new dream homes with elevated views toward Mount Maunganui.

The MagnumStone system provided the following benefits to the project:

• Can construct curves with a minimum 3.8m radius.
• Safe and easy to handle with the use of an excavator.
• Superb aesthetics add value to any site.