An evaluation of the tilt test for granular materials

Studies into rockfill have advocated the use of a tilt test to characterise the shear strength of coarse granular materials. The tilt test employs a simple split box, which is filled with rubble and then tilted until the upper box half slides off the lower box half. The angle at which this occurs is related to strength characteristics of the tested material, but the interpretation of this result is less than straight forward. This paper describes a systematic study of the tilt test on a series of gravels and mine wastes. The research shows that the tilt angle is sensitive to the tilt rate and the water content of the spoil, but that if the test is carried out in a systematic way, consistent results can be achieved. The results show that the tilt test is not a good discriminator of shear strength in waste rock materials. The tilt test is very sensitive to particle size, particle shape and relative density, but because of its very low confining stress, it is insensitive to the physical strength of particles. This means that the tilt test fails to discriminate reliably between weaker and stronger waste rock materials, for materials that are subjected to any significant amount of confining (normal) stress. It cannot be used as an alternative to direct shear testing to determine the shear strength parameters of mine spoil materials.