Conjola Mountain Re-alignment, NSW Conjola Mountain Re-alignment, NSW Conjola Mountain Re-alignment, NSW Conjola Mountain Re-alignment, NSW

Conjola Mountain Re-alignment, NSW

Project featuring Rock Filled Gabions

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General Information

The Mount Conjola Re-alignment project is located approximately 46kms south of Nowra along the Princess Highway. In 2006, the NSW Government, through the AusLink Strategic Regional Program announced a $10million funding budget for this project. This section of the Princess Highway is known for the high number of crashes, and low travel efficiency with traveler’s constantly experiencing delays and high traffic volumes. The project was divided into two stages with Stage 1 consisting of constructing the new Conjola Creek Bridge and road approaches and Stage 2 consisting of the Princess Highway re-alignment from Bendalong Road to the new Conjola Creek Bridge. The re-alignment of the highway was to improve both the current road safety and travel efficiency within this section of the Princess Highway.

BMD Constructions was awarded the contract for stage two works in 2006 with works involving bulk earthworks of approximately 200,000m3, 2.3km of new pavements; 120m long new concrete bridge, 2 underpasses (Bebo concrete arch), four reinforced soil panel walls and the construction of a side track to accommodate construction over a portion of the existing highway.

Conjola Mountain Re-alignment, NSW

The underpass at the northern end was a Humes™ Two-piece Classic Precast Concrete arch structure. Retaining Solutions scope of works was to design, supply & install rock filled mass gravity gabion headwalls surrounding the arch profile in accordance with AS4678 Earth Retaining Structures. The arch was approximately 55m long on a 6% grade. The arch and gabion headwalls were to support the permanent earth embankment load and the live loads surcharges (HLP320 & M1600 loading) from the Princess Highway. Douglas Partners Pty Ltd were the engaged geotechnical engineer whom verified foundation bearing capacities of in-situ medium, while the verification of the arch design was completed by University of Sydney using finite element modeling techniques.

Retaining Solutions was also engaged for the backfilling (spreading & compaction) of the arch structure and behind the gabion headwalls in accordance with “Humes™ Two-piece Classic Precast Concrete arch structure” strict backfilling procedures. Such guidelines detail minimum compaction requirements within 1m of arch profile and associated maximum weight (tonnes) of compaction equipment. Maximum backfill lift thicknesses to not exceed 300mm and most importantly the max backfill height difference between fill levels on opposite sides of arch to be 600mm.


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Project Specs

  • Application - Humes™ Classic Arch Headwalls
  • Product - Rock Filled Gabions
  • Finish - Basalt Rock
  • Volume - 1650m3
  • Max. Height - 9m
  • Length - 100m
  • Loadings - 25kPa
  • Design life - 100 years
  • Owner - NSW Roads and Maritime Services
  • Client - BMD Constructions Pty Ltd
  • Construction - 6 months

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