Mahdi, where did your idea come from?
The idea really came from the work we do every day. Our team does a lot of testing on tailings, and we started noticing that some materials are much harder to test consistently than normal sands (particularly silt-sized and transitional tailings).
Small differences in how we prepare a sample or run a test can sometimes change the result quite a bit. We realised there was an opportunity to improve the way we do this testing and make it more consistent within ATC Williams.
The proposal was also driven by the broader industry challenge around critical state line testing and how results are interpreted for tailings, where the behaviour does not always follow the same trends as clean sands.
What problem does your project solve?
The main problem is confidence in test results and ease of interpretation, especially when we’re trying to define the critical state line for tailings that can be sensitive to laboratory procedures.
Laboratory results are used to understand how tailings may behave and ultimately help assess the safety of tailings dams. We want to make sure the way we prepare and test the material gives us results that are as reliable and repeatable as possible. For some silts and mixed tailings, the state parameter is also much harder to estimate than it is for sands. That can make liquefaction assessment more uncertain.
The project is about reducing that uncertainty. It also means we can build more of this specialist capability within our in-house labs, rather than occasionally using external ones.
Above: The 80 mm diameter pedestal and schematic of slurry deposition system for triaxial specimen
Can you explain your approach?
We started by asking a simple question: “Is the way we currently prepare these samples giving us the best result?”
There are several different ways to prepare a tailings sample in the lab, including:
- moist tamping,
- static compaction,
- moist vibration, and
- slurry consolidation
The first stage is about trying these different methods and seeing how much they affect the test results. At the same time, we’re improving parts of our testing equipment to better control the test and get better-quality measurements.
We’re also looking at things like:
- saturation procedure,
- end-lubricated platens,
- load cells,
- displacement transducers, and
- data logging.
All those details can affect the quality of the test and the way the results are interpreted.
One interesting thing we saw before starting the project was just how sensitive some tailings can be. You can take essentially the same material, prepare it slightly differently, and potentially get a different response. That was really one of the reasons we thought this project was worth doing.
What is innovative about your project?
I would say the innovation is not necessarily in inventing a completely new test. What we’re doing is bringing together the right preparation method, improved equipment and a consistent testing process specifically for these difficult tailings materials.
The end goal is to have a method we trust and can repeat, allowing us to strengthen ATC Williams’ internal capability in critical state triaxial testing.
It’s also innovative because it links laboratory testing, equipment set-up and interpretation framework into one process, rather than treating them separately.
Above: Setting up the sample
What stage is the tool at now, and what is planned in the future?
We’re currently modifying our laboratory equipment and running some trial tests as part of Stage 1, which is dedicated to sample preparation and device improvement. Our focus is on:
- developing and trialling different sample preparation methods,
- improving the equipment where needed,
- running the testing, and
- documenting what works best.
The aim is to finish Stage 1 with a clear and consistent internal testing procedure that our labs can use going forward.
Stage 2 could involve working with a university on more advanced testing, including cyclic simple shear testing, hollow cylinder testing and CPTu calibration work. That would help extend the project into state-parameter-based liquefaction assessment for transitional tailings.