Software designer looking to ditch slope trial and error

Emily Roberts

Top image :
OptimalSlope co-founder, professor Stefano Utili
‘Optimal slopes are fed into a standard openpit optimisation’

Waste has always been a key focus in mining and OptimalSlope co-founder Stefano Utili believes it’s only becoming more critical. Yet, he says, ubiquitous strategic mine planning software still discounts pit-wall design from optimisation calculations.

“We bet this will not be the case in 10 years’ time,” Utili told InvestMETS.

“Pit walls will be designed according to slope topological optimisation theory which is what is implemented in OptimalSlope.”

Utili hopes the shift comes sooner, and market forces may yet work in his favour.

The seed for UK-based OptimalSlope – the company and its eponymous software – was planted 20 years ago when Utili was at university in Italy. His PhD professor had been to Japan and brought back a picture of a fortress moat from the 1700s that had unusual slope angles. They could not work out why the walls were concave rather than standard straight surfaces.

The question stayed with Utili, who dug deeper into the importance of slope design and researched methods to improve pit-wall design and slope stability in the mining industry. He knew openpit slope steepness had a big impact on financial returns. But steeper pit walls could not compromise the mine’s safety.

Professor of geotechnical engineering at Newcastle University since 2016, Utili has watched mines digging deeper and deeper to access ore, increasing the risk of slope failure and exponentially raising waste rock movement.

He maintains that if enough of the world’s openpit mines used his slope design software, the industry could cut its global carbon emissions by up to 20%.

As he pondered moats in Japan, Utili developed a design method based on the theory of limit analysis to calculate the stability of any slope shape using the thickness and properties of rock layers. Inputting geotechnical data typically used in mine block models, OptimalSlope software calculates optimal slope angles for mine pit walls.

In 2021, Utili demonstrated the new slope design software at a Kinross Gold mine.

In August last year, Utili and one of his PhD students, co-founder Andrea Agosti, won a 12-month incubator competition organised by the Grantham Institute at Imperial College in London which earned them a £20,000 grant.

“The commercial journey started there,” Utili said.

Further modelling with Kinross, mining software leader Datamine and US geotechnical consultant Call & Nicholas is said to have highlighted the potential to significantly reduce waste-rock production, with commensurate energy and carbon emission cuts, compared with standard pit slope designs.

The 58-year-old Lerchs-Grossmann algorithm for optimum openpit mine was turned into a best-selling mine design program by Jeff Whittle in the 1980s. Many other software companies have since entered the market.

Utili said geotechnical consultants were manually designing non-optimal slopes. It often meant designs were based on “experience and trial and error”.

“Experience is problematic since the stratigraphies of two mines are never the same no matter how closely geographically located, and trial and error is time consuming and produces pit walls that are far from optimal,” he said.

“Openpit optimisation requires slopes as an input and will treat the slope of each mine sector – provided as angles for blocks of the block model across the orebody – as a constraint in its economic optimisation.”

OptimalSlope generated a mathematically and geotechnically optimal slope.

“That is, the overall slope angle is as high as possible for a given prescribed factor of safety.

“The optimal slopes are then fed as input into the standard openpit optimisation.”

OptimalSlope is working with other software companies on integration, according to Utili.

“We have no integration [with Whittle] although we have run most of our case studies using OptimalSlope in combination with Whittle, having developed some scripts for passing the information between OptimalSlope and Whittle,” he said.

The cloud-based OptimalSlope software was “easily deployable and ideally placed for fast growth and integration in current strategic mine planning software packages”.

Utili says the company is working on the release of a new CAD-style graphical user interface, and building its first mine pushback with OptimalSlope-designed pit walls.

“The hard part is to build the software and get the trust of the market by providing consulting services mine by mine to showcase the financial and environmental gains that can be achieved,” he said.

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