Characterisation of Failure at a Large Landslide in SE Queensland by Geological Mapping, Laboratory Testing, Instrumentation and Monitoring

Abstract

Geotechnical studies undertaken for Cuts 3 and 4 of the South West Transit Corridor (SWTC) at Redbank Plains revealed complex geology, comprising trachyte flows extruded on top of sediments and basalt flows. The road cuttings form part of the Centenary Highway Extension, Springfield to Yamanto Package. The paper describes the investigation of a large-scale landslide encompassing Cuts 3 and 4, the nature and extent of which was revealed after the original design of the earthworks were substantially complete. In order to characterise the landslip mass, the geometry of the landslip mass and rate of movement was investigated using a large number of drill holes with inclinometer installations, which were monitored together with surface movement measurements. Instrumentation also included piezometers and observation wells. Laboratory testing was undertaken on material recovered from the shear surface, and compared with shear strength parameters derived from back analyses. Results of stability analyses are briefly described, and the monitoring data is presented and discussed. A Web-based data management system for providing an early warning system for potential future movements is described.