Borehole breakout in heterogeneous rocks using improved Voronoi model: Laboratory test and discrete element modeling

Borehole breakout in heterogeneous rocks using improved Voronoi model: Laboratory test and discrete element modeling

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Yingchun Li^a^,^*, Jiazhi Zhang^a, Changyi Zuo^b^,^**, Kang Duan^c

Journal of Rock Mechanics and Geotechnical Engineering | 2026, 18(5) : 3606 - 3622

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Journal of Rock Mechanics and Geotechnical Engineering | 2026, 18(5): 3606-3622

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Borehole breakout in heterogeneous rocks using improved Voronoi model: Laboratory test and discrete element modeling

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Yingchun Li^a^,^*, Jiazhi Zhang^a, Changyi Zuo^b^,^**, Kang Duan^c

Affiliations

^aDepartment of Civil Engineering, State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, 116024, China

^bSchool of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW, 2052, Australia

^cSchool of Civil Engineering, Shandong University, Jinan, 250100, China

Dr. Yingchun Li joined Department of Civil Engineering, School of Infrastructure Engineering, Dalian University of Technology, China in 2017. Dr. Li obtained BE in engineering from School of Mines, China University of Mining and Technology (CUMT), and his PhD from School of Mining Engineering, University of New South Wales, Sydney, Australia in 2016. His research interests focus on fundamentals and applications of rock mechanics in deep underground space and geo-resources engineering. He received several grants from the National Natural Science Foundation of China and the Ministry of Science and Technology, China. He has published more than 90 scientific papers.

Published: 2026-05-25 doi: 10.1016/j.jrmge.2025.06.010

Outline

Abstract

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Borehole instability in heterogeneous rocks poses a significant challenge in geo-energy engineering. The deformation and failure around boreholes are heavily mediated by the inherent heterogeneity of rocks. Here, we examined borehole breakout under hydrostatic pressure through both laboratory tests and numerical simulations on sandstone samples. Laboratory experiments demonstrated symmetrical V-shaped failures across various borehole diameters. To replicate these observations, we developed a heterogenous UDEC Voronoi model where the material heterogeneity was interpreted by assigning Weibull-distributed inter-grain contact parameters. The rigorous-calibrated numerical modeling can effectively capture the microscopic damage process and match the observed macroscopic failure modes. Simulations showed that reducing the borehole diameter increases the critical hydrostatic pressure required for borehole failure and prompts a shift from tensile to shear-dominated failure behavior. While stress anisotropy primarily governs the overall breakout morphology, rock heterogeneity influences the specific locations of crack initiation, leading to localized stress concentrations that shape the ultimate failure patterns. These results provide valuable insights into borehole stability in heterogeneous rocks and guide engineering design and pertinent risk assessment.

Key words

Borehole breakout / Rock heterogeneity / Discrete element model (DEM) / Weibull distribution / Sandstone / Voronoi model

Cite this Article

Yingchun Li, Jiazhi Zhang, Changyi Zuo, Kang Duan. Borehole breakout in heterogeneous rocks using improved Voronoi model: Laboratory test and discrete element modeling[J]. Journal of Rock Mechanics and Geotechnical Engineering, 2026 , 18 (5) : 3606 -3622 . DOI: 10.1016/j.jrmge.2025.06.010

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Funding

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National Natural Science Foundation of China(42472336)

Appendix

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Year 2026 volume 18 Issue 5

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Article Info

doi: 10.1016/j.jrmge.2025.06.010

Receive Date：2025-02-25
Online Date：2026-06-17
Published：2026-05-25

Article Data

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History

Received：2025-02-25
Revised：2025-06-25
Accepted：2025-06-29

Funding

National Natural Science Foundation of China(42472336)

Affiliations

^aDepartment of Civil Engineering, State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, 116024, China

^bSchool of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW, 2052, Australia

^cSchool of Civil Engineering, Shandong University, Jinan, 250100, China

Corresponding:

^* Corresponding author. E-mail addresses: yingchun_li@dlut.edu.cn (Y. Li)

^** Corresponding author. E-mail addresses: giselle02@163.com (C. Zuo).

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表12种不同金属材料的力学参数

科 Family	属数 Number of genus	种数 Number of species	占总种数比例 Percentage of total species (%)	属 Genus	种数 Number of species	占总种数比例 Percentage of total species (%)
鹅膏菌科Amanitaceae	2	11	5.26	鹅膏菌属 Amanita	10	4.78
小菇科 Mycenaceae	2	12	5.74	丝盖伞属 Inocybe	5	2.39
多孔菌科 Polyporaceae	8	14	6.70	蜡蘑属 Laccaria	5	2.39
红菇科 Russulaceae	3	23	11.00	小皮伞属 Marasmius	6	2.87
				小菇属 Mycena	11	5.26
				光柄菇属 Pluteus	5	2.39
				红菇属 Russula	17	8.13
				栓菌属 Trametes	5	2.39

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