Associated Event

Third International Slope Stability in Mining Conference
14-16 November 2023 | The Westin Perth, Western Australia

The Benefits of Employing Optimal Slope Profiles in the Design of Pitwalls Workshop

17 November 2023 | The Westin Perth, Western Australia
Target Audience

Geotechnical engineers and mine design professionals.


In open pit mining, there is a clear trend of excavating mines of increasing depths, from less than 50 m deep in the 1920s to more than 1 km in recent years. Owing to the increased efficiency of mining equipment and improved exploration techniques and technology, the orebodies left to be exploited reach depths of even 2,000 km from the ground surface. The deeper a mine, the higher the effect of pitwall steepness on the amount of waste rock excavated and, therefore, mine profitability. As such, designing pit walls to be safe and as steep as feasible at the same time has never been more important. The steepness of mine pitwalls significantly affects not only mine profitability, but also carbon footprint since mining operations are primarily responsible for carbon emissions.

Traditionally, the design of pitwall inclinations is carried out by geotechnical teams with little interaction with mining engineers. Usually, the geotechnical engineer establishes the maximum inclination of any pitwall to be excavated within the various geotechnical domains of the mine. The design is performed following a prescribed Factor of Safety (FoS) chosen based on the risk profile of the mining company. The mining engineer then uses various software packages, e.g. Datamine Studio NPVS, Geovia Whittle, Hexagon MinePlan, Maptek, etc. to compute pushbacks and the ultimate pit limit by performing a strategic pit optimisation with the maximum acceptable pitwall inclination acting as a constraint. No further interaction occurs until the geotechnical team is asked to verify the stability of the final pitwalls produced by the pit optimisation software. However, it is well known that the maximum inclination of a slope is a function not only of the prescribed FoS but also of slope height. Therefore, imposing a pitwall maximum inclination, irrespective of the pitshell depth, implies that the current design methodology gives rise to suboptimal designs where often the pitwall inclination is either less steep (design overly conservative) or steeper (a below-target FoS is adopted) than what it could be.

To overcome current limitations, participants will be introduced to a design methodology where pitwall inclinations are selected, accounting for the pit depth, and integrated into the strategic mine design (Utili et al. 2022).

Preliminary program*

Times Topics
Mining slope failure mechanisms
Main factor controlling design of pitwall
Catch bench design
Catch bench design – continued
Pitwall design by OptimalSlope
McLaughlin gold mine case study
McLaughlin gold mine case study – continued
Introduction to 3D anisotropy
Introduction to 3D anistropy continued
Pitwall design in anisotropy of rock masses
Round table with questions and answers

*Program subject to change

This methodology is made possible by iterating between pit optimiser and geotechnical pitwall design (Figure 1). The improvements in financial returns that can be gained by adopting the proposed methodology will be showcased for two case studies of real gold and copper mines. Also, in the current design practice, pit wall profiles are often designed to be planar in cross-section, especially within each rock layer with constant over-depth inter-ramp angle. A new slope design software, OptimalSlope[1], can determine geotechnically optimal pitwall profiles of depth varying inclination for the design of each sector of the mine. OptimalSlope seeks the solution of a mathematical optimisation problem where the overall steepness of the pitwall, from crest to toe, is maximised for an assigned lithology, rock properties and FoS. The adoption of overall steeper profiles leads to further reduction in the amount of waste rock and, consequently, the stripping ratio. For each mine case study, both financial gains (in terms of NPV) and environmental gains (measuring the reduction in carbon footprint and energy consumption) are assessed. 

[1] See

Fig 1 Pit design process: (a) Flowchart illustrating the iterative process followed to determine the ultimate pit limit (UPL) and pushbacks. Note that the process is the same irrespective of the shape of the adopted pitwall profiles. (b) Slope (pitwall) height versus overall slope angle for different FoS values and profile shapes (planar profiles in orange and optimal profiles in blue). Note the curves were derived for the specific geotechnical parameters of the case study mine. A different set of strength parameters would produce different curves, however, the qualitative trend of the curves is valid irrespective of the rock strength values (after Utili et al. 2022)

Recently, OptimalSlope has been extended to anisotropic rock masses featured by several joint sets and beddings (Agosti et al. 2022b). Participants will be introduced to the recently presented Cylwik method to estimate anisotropic equivalent cohesion (c) and internal friction (φ) parameters for a jointed rock mass from information on joint orientation and persistence for all the 2D cross-sections of the pit relevant for design purposes (Cylwik 2021). These direction-dependent c and φ equivalent parameters, in terms of dip of the failure surface versus c and dip of the failure surface versus φ functions, can be input into OptimalSlope to obtain the optimal pitwall profile. A dataset of joints in a cretaceous aged siltstone with eight different joint sets and one main bedding where an open pit is to be excavated will be illustrated as a case study.

  1. Utili, S, Agosti, A, Morales, N, Valderrama, C, Pell, R & Albornoz, G 2022a, ‘Optimal pitwall shapes to maximise financial return and decrease carbon footprint of open pit mines’, Mining Metallurgy & Exploration,
  2. Agosti, A, Cylwik, S & Utili, S 2022b ‘Geotechnically optimal profiles to maximize mine pit-wall steepness in anisotropic bedded sedimentary rocks’, International Journal of Mining and Technology, under review.
  3. Agosti, A, Utili, S, Valderrama, C & Albornoz, G 2021, ‘Optimal pitwall profiles to maximise the overall slope angle of open pit mines: the McLaughlin Mine’,
    in PM Dight (ed.), SSIM 2021: Second International Slope Stability in Mining, Australian Centre for Geomechanics, Perth, pp. 69–82,
  4. Agosti, A, Utili, S, Gregory, D, Lapworth, A, Samardzic, J & Prawasono, A 2021b, ‘Design of an open pit goldmine by optimal pitwall profiles’, CIM Journal,
    vol. 12, no. 4, pp. 149–168,
  5. Cylwik, SD 2021, ‘Three-dimensional anisotropic shear strength of jointed rock masses’, Proceedings of the 55th US Rock Mechanics/Geomechanics Symposium, American Rock Mechanics Association, Alexandria.
Workshop presenter

Professor Stefano Utili
Professor of Geotechnical Engineering, Newcastle University, UK
Founder, OptimalSlope Ltd, UK

Stefano is a chartered engineer and fellow of the Institution of Civil Engineering. He is a member of the International Technical Committee 208 ‘Slope Stability in Engineering Practice’, serves on the editorial board of several prestigious international journals such as Engineering Geology, Rock Mechanics & Rock Engineering, and Landslides, and has published extensively on the assessment of slope stability and the design of mine pitwalls.

Scott Cylwik
Geotechnical Project Manager, Call & Nicholas, USA

Scott is a geotechnical project manager at Call & Nicholas with 15 years’ experience in mine slope stability. He is a professional registered engineer in Arizona, California, and Colorado. His areas of specialisation include rock mechanics, soil mechanics, laboratory testing, and open pit slope angle optimisation. He has published technical papers on oriented core data, probabilistic slope analysis, and rock mass shear strength.