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Determination of instability modes and fracture mechanics of hard, thick-bedded rocks surrounding underground openings (ONMELS)
https://www.croris.hr/projekti/projekt/16358
Funding source: European Union (NextGenerationEU)
Duration: 1. 10. 2025. – 30.9.2029
Project Leader: Assoc. Prof. Zlatko Briševac, PhD
Budget: 59.600,75 EUR
Call for project proposals: Poziv za financiranje institucionalnih istraživačkih projekata financiran iz izvora 581 – Mehanizam za oporavak i otpornost (2025.) / Call for Funding of Institutional Research Projects Funded from Source 581 – Recovery and Resilience Facility (2025)
Project summary
The identification of instability modes and fracture mechanisms is essential for predicting the behaviour of rock masses surrounding underground openings in mines and tunnels. Rock mass behaviour is strongly influenced by the properties of the intact material, the characteristics of structural discontinuities and the rock mass itself, as well as by the size and geometry of underground openings and the prevailing stress conditions. In general, rock masses may behave as continuous, discontinuous, or quasi-continuous geotechnical media; however, their behaviour can be considerably more complex, particularly in the case of hard, thick-bedded rocks. A wide range of analytical and numerical methods has been developed worldwide, primarily based on the principles of continuum or discontinuum mechanics. Nevertheless, satisfactory solutions for complex rock mass behaviour remain limited, and the conditions under which such behaviour occurs are still not fully understood. Moreover, robust predictive models that relate rock mass behaviour to material properties, discontinuities, mass characteristics, and stress conditions have yet to be adequately established. In this regard, comprehensive laboratory and field investigations are planned to determine the relevant material, discontinuity, and rock mass properties. These investigations will be complemented by the application of analytical and numerical modelling techniques aimed at assessing the influence of individual parameters on overall rock mass behaviour, including instability modes and fracture mechanisms. The proposed research is expected to contribute new scientific insights into the role of key controlling factors and to support the development of improved models and methods for predicting the behaviour of rock masses around underground openings.
Project Goals:
The project has four main objectives:
- To conduct the necessary laboratory and field tests and measurements in order to achieve the planned results within this research project and to enable their potential application in future projects addressing similar issues.
- To carry out detailed analyses using analytical and numerical calculation methods to determine the key influencing parameters.
- To determine the influence of individual characteristics of the intact rock material, the properties of structural discontinuities, and the characteristics of the rock mass on overall behaviour, including the development of deformations, instability modes, and fracture mechanisms of strong, thick-bedded rocks surrounding underground openings.
- To develop models and methods for predicting rock mass behaviour in relation to material properties, the characteristics of structural discontinuities and the rock mass, as well as the size and geometry of underground openings and the prevailing stress conditions.
By achieving these scientific research objectives, additional long-term goals would also be indirectly accomplished:
- To strengthen the project team by expanding research resources through the acquisition of necessary equipment and software licences, and by developing new knowledge and skills that will support future research activities.
- To publish a series of thematic scientific papers in journals indexed in WoS or Scopus, as well as to present the results at national and international scientific conferences.
Team members
Read more| Members from faculty: | |||
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Assoc. Prof. Zlatko Briševac, PhD – project manager University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Croatia |
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Assoc. Prof. Petar Hrženjak, PhD – deputy project manager University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Croatia |
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Prof. Emer. Slavko Vujec, PhD University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Croatia |
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Full Prof. Antonia Jaguljnjak Lazarević, PhD University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Croatia |
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Full Prof. Dalibor Kuhinek, PhD University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Croatia |
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Assoc. Prof. Tanja Mališ, PhD University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Croatia |
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Assist. Prof. Anja Vrbaški, PhD University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Croatia |
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Nikolina Kovačević senior lecturer University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Croatia |
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Full Prof. (tenured) Damir Lazarević, PhD University of Zagreb, Faculty of Civil Engineering |
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Research Methodology
Read moreTo achieve the expected results and project objectives, a research methodology and work plan have been established. These include laboratory testing of the physical and mechanical properties of intact rock material and discontinuity surfaces; field measurements of discontinuity orientations; in situ testing of stress conditions and rock mass deformability; determination of flexural strength of test blocks within the rock mass; and monitoring of underground opening convergence, deformations, and displacements along discontinuities. In addition, detailed numerical analyses will be carried out on the developed models. Based on all obtained results, models for predicting rock mass behaviour around underground openings will be developed, together with methods for calculating rock mass strength, pillar load-bearing capacity, and the load-bearing capacity of roof strata.
The research will begin with a comprehensive review and collection of relevant scientific and technical literature related to the problem under consideration. Laboratory testing will be conducted to determine the fundamental physical and mechanical properties of the material, including density, porosity, uniaxial compressive strength, deformability, triaxial strength, and flexural strength. Field investigations will include the determination of in situ stress conditions and rock mass deformability, as well as in situ flexural strength testing of rock blocks within the rock mass. Measurements of underground opening convergence, material deformation, and displacement along characteristic discontinuities will be performed throughout the duration of the project under real mining conditions during underground extraction of architectural and construction stone blocks. All tests and measurements will be carried out on materials and at locations within selected deposits composed of strong, thick-bedded rocks in Croatia.
The Geomechanical Laboratory of the Faculty of Mining, Geology and Petroleum Engineering is equipped with the essential basic equipment, devices, and measuring instruments required for laboratory and field testing and measurements. However, replacement of worn components of the computer-based measurement system and faulty equipment is required, as well as the acquisition of additional equipment and devices to enable the implementation of testing procedures with specialised process control.
Numerical analyses will be performed on established models for various possible combinations of material properties of the deposit layers, discontinuity orientations, underground opening dimensions, and stress conditions. Numerical model calculations will be carried out using licensed software to be procured through this project. Based on the results of all tests, measurements, and numerical analyses, predictive models of rock mass behaviour around underground openings will be developed using selected advanced technological tools applicable to this type of problem. Methods for calculating rock mass strength, pillar load-bearing capacity, and roof strata capacity will be developed using Microsoft Excel. A guiding principle in the development of both the models and calculation methods is that they should be as simple and user-friendly as possible for engineers dealing with this issue, particularly during preliminary stability analyses of underground openings in strong, thick-bedded rocks.
Dissemination
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