Geotechnical Investigation into Causes of Failure of a Gabion Retaining Wall

This paper describes the post-failure analysis of a 26m long x 4m high gabion retaining wall located in a suburb of Johannesburg, South Africa. The wall had been built just beyond the toe of a natural slope with most of the gabion units resting on the bed of a small river. The river bed soils consisted of approximately 2.5 m of soft, dark-grey, silty clay underlain by massive granite bedrock. The water table at the toe of the wall was within 0.1 m of the river bed surface. Failure of the wall occurred over the weekend after backfilling to grade behind the wall had been completed. Stability analyses were conducted using both total (undrained) and effective (drained) shear strength parameters for the clay. The results of the analyses showed that the wall should be stable with FS = 1.2 for effective stress parameters and that the wall should be unstable with FS = 1.0 for undrained strength parameters. The details of the testing program and the selection of strength parameters is described in the paper