Combining traditional tunneline technology with modern day rehabilitation techniques enabled Downer PipeTech to submit and provide a solution to extend the life of an existing set of culverts that crossed the M1/Princes Highway outside The University of Wollongong.

The challenge

The prime objective of the work was to provide structural integrity and equalise the bores of a triple cell culvert that passed beneath one of the busiest arterial routes in Australia and to achieve a design life of 100-years.

A secondary consideration was to devise a methodology and a sequence of works that caused the least disruption to the motorway that carries over 18,000 vehicle movements a day just two metres above the top of the culverts.

The University culverts carry the Dallas Street branch of Fairy Creek which crosses under the motorway via a three-cell precast concrete pipe.

Over the years as the Princes Motorway was upgraded and widened, the original 1350mm triple culvert set was extended to take additional traffic lanes. The northern extension, however, was sized at 1200mm, which at times of heavy rain, was restricting the flow of water into the culverts causing flooding to the upstream creek valley and threatening local property and the university campus.

The solution

The project identified the probability of one or more of the culverts becoming blocked under a one-in-100-year storm event; therefore the feasibility review recommended that the pipes at the upper ends of the culvert set be enlarged to a common profile similar to the remainder of the culvert.

It also recommended that an inclusion of debris barriers with vehicle access be installed to the culvert entrance for access to undertake maintenance and routine debris clearance under the project scope.