Barton, NR 2008, 'Shear Strength of Rockfill, Interfaces and Rock Joints, and their Points of Contact in Rock Dump Design', in AB Fourie (ed.), Rock Dumps 2008: Proceedings of the First International Seminar on the Management of Rock Dumps, Stockpiles and Heap Leach Pads, Australian Centre for Geomechanics, Perth, pp. 3-17, https://doi.org/10.36487/ACG_repo/802_1
(https://papers.acg.uwa.edu.au/p/802_1_Barton/)
Abstract: The peak shear strength of rock joints obtained from direct shear tests, and the peak shear strength of 
rockfill, as interpreted from large-scale triaxial tests, have common non-linear strength envelopes. An 
extremely low stress index test for rock joints, the tilt test, with an apparent normal stress as low as 
0.001 MPa when sliding occurs, can also be performed to characterise rockfill. However for rockfill or rock 
dumps, larger samples with relevant particle sizes are desirable. Some full-scale tests at a dam site in Italy, 
using a 2x2x5 m tilt-shear test, were able to sample the as-compacted-as-built rockfill, with no need for 
using parallel (model) grading curves with reduced-sized particles. Interfaces between the rockfill or rock 
dump and eventual rock foundations, can be handled with similar shear strength estimation methods. In each 
case, a low-stress index test result is extrapolated to full scale and to engineering stress level by related non-
linear strength laws. It is possible to estimate each through inexpensive characterisation. The non-linear, 
stress-dependent friction angles suggest that large rock dumps with constant slope angle will have strongly 
reducing factors of safety from top to bottom and from outside to inside.