Centurion is renowned for sinkholes. The PRASA line running from Johannesburg to Pretoria experienced numerous sinkholes between Botha Avenue and the Centurion Station. Most of these were rehabilitated, but upon further investigation it was found that maintenance should occur.


On this project, it was not possible to stop the trains for sinkhole maintenance. The decision was made that compaction grouting should be done to stabilise the railway. It was important to grout under the entire railway – both northbound and southbound – without disrupting the traffic. This project called for the holes to be drilled at angles varying between 15 – 55 degrees. A downstage drilling approach was adopted for this project.