2015 Large Scale Testing of Mine Spoil

This paper presents the results of an experimental study in which a strong Permian mine spoil from the Hunter Valley, Australia was tested under unsaturated and saturated conditions, using a large direct shear machine. The direct shear machine, with a specimen size of 720mm x 720mm x 600mm and a normal stress capacity of 4.5 MPa, was designed and constructed at the University of Newcastle. The spoil material tested is dominated by siltstone with some fine to medium grained sandstone fragments. The large size of the test device allows specimens with particles as large as 100mm to be tested. Tests under unsaturated and saturated conditions recorded considerably different strengths, with peak friction angles of spoil in the unsaturated condition being as much as 6 degrees greater than the same spoil in a saturated state. The reduced strength under saturated conditions is attributed to the effects of reduced matric suction within the rock fragments of the spoil, and the effect this has on the basic rock fragment strength.