Senior principal Patrick Wong said the soft soil was particularly deep and variable in the Ballina region of northern New South Wales, creating the potential for embankment instability and differential settlement issues.
The challenge facing Coffey Geotechnics is magnified because of weak planes within the surrounding rock, the condition for a possible large-scale failure when the Ballina Bypass cuts through existing hills.
“Our role is to provide the RTA with solutions that will avoid road embankment failure, as well as loss of equipment and injury during construction. We also need to overcome the post-construction settlement in the soil, otherwise a bumpy road will result,” Patrick said.
Coffey Geotechnics has had a long relationship with the RTA on the project, dating back to 2005 when it carried out a detailed site investigation.
“We advised the RTA on soft ground treatments – which included indications on costs, time and risks. This enabled the RTA to make informed decisions about the construction program.
“And proudly we have been able to introduce a number of methods to overcome these difficult ground conditions,” he said.
Vacuum consolidation is one of the innovative solutions introduced by Coffey Geotechnics. Being used in Australia for the first time, it will help to overcome the 25-metre deep, soft clay around one of the proposed bridge approaches.
Other soft ground treatment solutions such as lightweight fill, deep soil mixing and dynamic replacement are also being considered.
Patrick said because of the solutions provided by Coffey Geotechnics, the timetable for the highway was expected to be more than halved from the originally planned 13-year construction period.
RTA is currently forming an alliance to deliver the Ballina Bypass project and has nominated Coffey as one of the partners.
“This is the first time the RTA has nominated a consultant to be a full alliance partner prior to the selection of the alliance group,” he explained.
For more information on ground improvement techniques, contact: Patrick Wong patrick_wong@coffey.com (+61) (2) 9911 1000.
