Parkes Rd, Collaroy  Plateau

  • Client: Private Individual
  • Principal: Northern Contracting Group
  • Date: March 2015

Project Description

Northern Contracting Group (NCG) were engaged by CMS Surveyors (the client superintendent) to undertake stormwater drainage, in ground services and concrete driveway construction relating to a 2 lot subdivision.

The drainage works consisted of construction of a reinforced concrete and corefilled block wall onsite detention tank with a bondek trafficable roof slab. Upstream of the OSD was a new kerb inlet pit and lintel linked with 150mm PVC stormwater pipe. The 150mm pipe continued on the downstream of the OSD tank. Headwall and scour protection was installed

There was the requirement to install stormwater infrastructure within the council easement that consisted of 2 600x600mm junction pits and 375mm RCP and a headwall and scour protection to suit.

In-ground service provisions consisting of conduits and connection for water, gas, electrical, Telstra, NBN and Foxtel were including in our scope of works. As there were 2 lots we were required to run 2 sets of conduits on either side of the new driveway in the designated service easement. The water had the requirement for under-road boring in order for connection with the existing watermain. Horizontal boring was used in this instance

The concrete driveway included the demolition and removal of the existing driveway as this didn’t meet the current council grade specification. Construction was based on 100mm of recycled DGB20 subgrade and 200mm thick concrete road pavement. Due to the steepness of the site reinforced edge beams were keyed into the existing subgrade. The existing council crossover and layback were replaced in accordance with the council specification

One challenge NCG encountered was what the existing site subgrade was saturated to the point that remediation was required. NCG’s proposal was to excavate to 1m depth for the full width of the driveway for approximately 15m long. We replaced the saturated fill with recycled 40/70mm aggregate to bridge the water-charged ground. A layer of tensar geogrid was installed for additional stability with a separation layer of geofabric covering the top. This allowed for the subbase to be consistently compacted to ensure suitable founding to meet the compaction requirements for the concrete road pavement. The consulting engineer was comfortable with this construction method and certified the project in accordance with council conditions

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