Grabinsky, M, Jafari, M, Thompson, B & Veenstra, R 2026, 'Interpreting laboratory liquefaction test results: the importance of 
confining pressure to unconfined compressive strength ratios', in AB Fourie, M Horta, M Oliveira & S Wilson (eds), Paste 2026: Proceedings of the 28th International Conference on Paste, Thickened and Filtered Tailings, Australian Centre for Geomechanics, Perth, pp. 1-10, https://doi.org/10.36487/ACG_repo/2655_15
(https://papers.acg.uwa.edu.au/p/2655_15_Grabinsky/)
Abstract: Laboratory liquefaction testing programs on cemented paste backfills (CPBs) have been based on methods used in conventional geotechnical earthquake engineering. The conventional approach emphasises the need to understand the soil’s initial state (void ratio and effective confining stress) with respect to the critical state line. Laboratory testing of undisturbed or (more commonly) reconstituted samples is often conducted at an initial effective confining pressure of 100 kPa. There is an assumption in cyclic liquefaction testing that the test results depend on the ratio of cyclic shear stress to initial effective confining stress, regardless of the initial effective confining stress magnitude. However, is this assumption valid for sands (and silts) with artificial cohesion created by binder hydration?
The authors recently published a retrospective analysis of monotonic triaxial test results on CPB where both undrained tests with porewater pressure measurements as well as drained tests with volume change measurements were used. It was shown that the ratio of initial effective confining stress to unconfined compressive strength (UCS) can be considered a ‘state parameter’ used to predict the extent to which porewater pressures (in undrained testing), or volume changes (in drained testing) would develop, regardless of the UCS magnitude. This framework will first be summarised and its application demonstrated to published triaxial test results. Then, the approach is extended to cyclic testing using published test results from both triaxial and simple direct shear testing programs.
A major finding from this work is that commonly used heuristics such as “X kPa UCS makes CPB liquefaction resistant” are naive and should be avoided because they do not account for the varying effective confining stress magnitudes that exist in different design scenarios, nor the absolute magnitude of the cyclic shear stress. The findings from this study can also be used to better design future experimental programs to assess cemented paste liquefaction potential for projects both underground and on surface.

Keywords: cemented paste backfill, liquefaction resistance, minimum binder content