The Hume Highway (M31) is arguably Australia’s most important piece of transport infrastructure carrying around 45,000 cars, trucks and bases per day which equates to $22 billion dollars’ worth of goods each year.
In 2006 it was proposed to undermine the Hume with a series of long wall panels near Douglas Park, NSW, which would obliquely undermine the dual carriageway causing subsidence of up to 1 m. At the time the potential economic loss due to mining impacts on M31 without mitigation was estimated to be around $125M. At the time PSM were invited to be part of a technical committee that would oversee the prediction, measurement and mitigation of impacts. Six years later the fourth longwall panel is nearing completion while the mitigation strategies have allowed the highway to operate continuously without incident and with minimal delays to traffic.
Key to the success of the project is the ability to accurately measure the response of the pavement under mining induced strains and the mitigatory pavement compression relief mechanisms. A system of around 600 Optical Fibre Bragg Gratings (FBG) are used to monitor changes in pavement strain at 10 m intervals above the workings. The increases in compressive strain are subsequently relieved by closure within a network of 80 slots, each pre-constructed transversely through the full depth of the pavement structure and fitted with crackmeters to measure closure. Additional monitoring elements include crack meters to measure differential expansion across bridge joints, a shape array to monitor any shear movement below the base of the Douglas Park Bridges and manual inclinometers and survey marks.
The success of the monitoring system has provided the ability to correlate changes in ground strain, pavement strain and strain relief due to slot closure. This paper provides an overview of the system with a focus on the way in which strains and movements are evaluated and verified across alternate measuring systems.
Swarbrick G., Meers P., Lee Shoy D., Kay D. and Buys H. (2015), Monitoring Pavement Relief of the Hume Highway During Undermining, Ninth International Symposium on Field Measurements in Geomechanics, Sydney, Australia, 8 September 2015, Australian Centre for Geomechanics, accepted for publication.