The Possibility of Undrained Failure in Bowen Basin Spoil Piles

For many of the spoil pile failures in the Bowen Basin the use of residual shear strength parameters in back analysis cannot be justified. The shear strength parameters of a range of coal mine spoil from the Bowen Basin have been measured using direct shear techniques. If the measured drained fully remoulded strength parameters are used in the back-analyses failure does not result. It is shown that failures could have initiated as a result of undrained conditions developed along the base of the spoil pile. Rates of drainage and gain in undrained shear strength are compared with the rate of mining.