At the request of the Government of Western Australia Public Transport Authority (PTA), we carried out a comprehensive condition assessment of three Perth Metro rail lines using geophysical and geotechnical test methods. During the investigation over 120 km of rail track was tested using multi-frequency Ground Penetrating Radar (GPR) supplemented with test pits made at 2 km intervals.

The GPR acquisition system was mobilised on a rail trolley with the GPR antennas housed in sleds suspended over the track centre line and on either side of the rail sleeper. Positioning was achieved using a GPS receiver linked to the GPR acquisition computers and a digital odometer running on the rail track.

The acquired data was analysed to assess the condition of both the rail ballast and underlying formation material along the Perth heritage lines. The original construction of these lines involved laying track and ballast directly on scraped formation material rather than on engineered formation as is the current practice. Consequently, sections of the original line may exhibit track pumping and formation subsidence leading to an increased likelihood of track and rail wear and ongoing maintenance costs.

The GPR dataset calibrated with the test pit logs provided information pertinent to the ballast condition including the definition of thickness, moisture content and fouling; and formation condition including thickness, interlayer condition, identified defects and material type. The results of the investigation enabled the demarcation of the original formation type with sections that have since been remediated to consist of engineered formation material.

The results of the investigation were provided in AutoCAD, GIS and spreadsheet formats showing the ballast and formation layer thicknesses and conditions together with an assessment of track sections defined as being of high, moderate and low priority for future remediation.