Tensile-shear collaborative fracturing in hard rock induced by a controllable free surface: Mechanism and application

Abstract

In deep hard rock mining, high confining pressure inhibits tensile failure, leading to low efficiency and severe tool wear in conventional mechanical rock breaking methods. To solve this problem, we propose a Controllable Free Surface Induced Tensile-Shear Collaborative Fracturing (CFS-TSCF) method. The method pre-forms an engineered controllable free surface (CFS) to reconfigure the local stress field, enabling a specialized device (FIPFD) to apply directional tensile-shear loads for low-energy breaking. A multi-scale approach integrating lab AE tests, DEM simulations, and field verification investigated the fracture mechanism and performance. Results revealed a predominantly tensile-driven (>50%) process. The CFS transforms the rock’s triaxial compression into a specific stress path. This path, dominated by directional tension and constrained by lateral compression, guides the fracture along a low-energy channel. This also dictates the micro-mechanism’s evolution from central quasi-tensile to peripheral tensile-shear failure. Field trials in hard rock (>200 MPa UCS) validated the method, demonstrating controllable, blocky spalling and achieving an average mining efficiency of 52.03 t/h. This research validates the CFS-TSCF method, offering a new technical paradigm for safe, efficient, continuous hard rock mining.

Keywords

Hardrock breaking / Controllable free surface / Fracturing mechanism / Stress path / Acoustic emission / Non-blasting mining

CRediT authorship contribution statement

Chenliang Hao: Writing – review & editing, Writing – original draft, Visualization, Validation, Methodology, Investigation, Data curation, Conceptualization. Longjun Dong: Writing – review & editing, Supervision, Funding acquisition, Conceptualization. Fangzhen Fan: Writing – review & editing, Validation, Software, Investigation. Xuewei Li: Writing – review & editing, Validation, Investigation. Ju Ma: Writing – review & editing, Supervision, Methodology. Yihan Zhang: Writing – original draft, Visualization, Methodology, Data curation.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors wish to acknowledge the financial support from the Funds for Distinguished Youth Funds of the National Natural Science Foundation of China (No. 52425403), the National Science and Technology Major Project of the Ministry of Science and Technology of China (No. 2025ZD1010903), the State Scholarship Fund of the China Scholarship Council (No. 202506370162), and the Hunan Province Graduate Research Innovation Project of China (No. CX20230168).

References

[1] Li XB, Gong FQ, Tao M, Dong LJ, Du K, Ma CD, et al. Failure mechanism and coupled static—dynamic loading theory in deep hard rock mining: a review. J Rock Mech Geotech Eng 2017; 9(4):767-82.

[2] Dong LJ. Multi—Source Acoustics of Rock Mass and its Applications. Beijing: Science Press; 2023.

[3] Xie HP, Gao MZ, Fu CH, Lu YQ, Yang MQ, Hu JJ, et al. Mechanical behavior of brittle ductile transition in rocks at different depths. J China Coal Soc 2021; 46(3):701—15. in Chinese.

[4] Dong LJ, Hao CL, Sun DY, Zhang YH, Yan XH, Wang JC, et al. Geosound monitoring for early warning prevention control of mine roof hazards. Journal of Mining and Strata Control Eng 2025; 7(4):043541. in Chinese.

[5] Rostami J. Performance prediction of hard rock Tunnel Boring Machines (TBMs) in difficult ground. Tunn Undergr Space Technol 2016; 57:173-82.

[6] Cai MF, Li P, Tan WH, Ren FH. Key engineering technologies to achieve green, intelligent, and sustainable development of deep metal mines in China. Engineering 2021; 7(11):1513—7.

[7] Liu CY, Yang JX, Yu B. Rock—breaking mechanism and experimental analysis of confined blasting of borehole surrounding rock. Int J Min Sci Technol 2017; 27(5):795-801.

[8] Zhu ZM, Xu WT, Feng RQ. A new method for measuring mode—I dynamic fracture toughness of rock under blasting loads. Exp Tech 2016; 40(3):899-905.

[9] Pu CJ, Yang X, Zhao H, Chen ZL, Xiao DJ. Numerical investigation on crack propagation and coalescence induced by dual—borehole blasting. Int J Impact Eng 2021; 157:103983.

[10] Cai YZ, Xu ZH, Liu YF, Chen XZ, Qi WC, Liu L. Weakly confined slotted cartridge blasting in jointed rock mass. Theor Appl Fract Mech 2024; 134:104695.

[11] Xiao CL, Yang RS, Ding CX, You YY, Tang WD. Multi—scale research on blasting damage of rock based on fractal theory. Rock Mech Rock Eng 2024; 57(8):5899-911.

[12] Liu GF, Feng XT, Feng GL, Chen BR, Chen DF, Duan SQ. A method for dynamic risk assessment and management of rockbursts in drill and blast tunnels. Rock Mech Rock Eng 2016; 49(8):3257-79.

[13] Feng GR, Hao CL, Wang PF, Guo J, Qian RP, Wen XZ, et al. Mechanism of asymmetric deformation of mining roads under close goaf and control measure. Journal of China University of Mining & Technology 2022; 51(4):617—31. in Chinese.

[14] Hamzaban MT, Rostami J, Dahl F, Macias FJ, Jakobsen PD. Wear of cutting tools in hard rock excavation process: a critical review of rock abrasiveness testing methods. Rock Mech Rock Eng 2023; 56(3):1843—82.

[15] Li XB, Zhou J, Wang SF, Liu B. Review and practice of deep mining for solid mineral resources. The Chinese Journal of Nonferrous Metals 2017; 27(6):1236-62. in Chinese.

[16] Palaniappan SK, Pal SK, Chinnasamy M, Rathanasamy R. Efficiency of rock cutting and wear behavior of coated bits via lab—scale linear rock—cutting machine: experimental approach. Int J Geomech 2023; 23(2):06022041.

[17] Li C, He SF, Hou WT, Ma D. Experimental study on expansion and cracking properties of static cracking agents in different assembly states. Int J Min Sci Technol 2022; 32(6):1259—72.

[18] Wang C, Zhang Q, Wang J, He MC, Guo S. Enhancing directional rock fracturing with instantaneous expanding slit former technology. Int J Geomech 2025; 25(9):04025174.

[19] Liu SY, Li HS, Cheng G. Numerical and experimental investigation on rock breaking performance with hydraulic splitter. Tunn Undergr Space Technol 2020; 96:103181.

[20] Kim M, Xu TZ, Kim H, Sagong M, Zi G. Experimental and numerical studies on splitting fracture of rocks using different bit heads. KSCE J Civ Eng 2023; 27(5):2217—34.

[21] Li HS, Wu ZJ, Liu SY, Gu CC, Zhang XD, Xu PP, et al. Rock fracturing mechanism and arrangement of fracturing holes using hydro—mechanical splitters. Eng Fract Mech 2024; 301:110055.

[22] Li HS, Liu SY, Cheng G, Guo CW. Numerical investigation on rock—fracturing mechanism by using splitter under hole assistance. Shock Vib 2019; 2019:4395729.

[23] Zhang JL, Yang FW, Cao ZG, Xia YM, Li YC. In situ experimental study on TBM excavation with high—pressure water—jet—assisted rock breaking. J Cent South Univ 2022; 29(12):4066-77.

[24] Liu SY, Zhou FY, Li HS, Chen YQ, Wang FC, Guo CW. Experimental investigation of hard rock breaking using a conical pick assisted by abrasive water jet. Rock Mech Rock Eng 2020; 53(9):4221—30.

[25] Liu SY, Cui YM, Cui S, Li ZQ, Zhou FY, Wang HD. Experimental investigation on rock fracturing performance under high—pressure foam impact. Eng Fract Mech 2021; 252:107838.

[26] Dong LJ, Hao CL, Fan FZ, Li XW. A self—adaptive excavation robot for stress environment reconstruction and its excavation method. China Patent: CN119288426B; 2025—10—31.

[27] Feng XT, Kong R, Zhang XW, Yang CX. Experimental study of failure differences in hard rock under true triaxial compression. Rock Mech Rock Eng 2019; 52(7):2109-22.

[28] Chang J, Xu JQ, Mutoh Y. A general mixed—mode brittle fracture criterion for cracked materials. Eng Fract Mech 2006; 73(9):1249-63.

[29] Benzeggagh ML, Kenane M. Measurement of mixed—mode delamination fracture toughness of unidirectional glass/epoxy composites with mixed—mode bending apparatus. Compos Sci Technol 1996; 56(4):439-49.

[30] An HM, Mu XH. Contributions to rock fracture induced by high ground stress in deep mining: a review. Rock Mech Rock Eng 2025; 58(1):463-511.

[31] Dong LJ, Zhang YH, Bi SJ, Ma J, Yan YH, Cao H. Uncertainty investigation for the classification of rock micro—fracture types using acoustic emission parameters. Int J Rock Mech Min Sci 2023; 162:105292.

[32] Di YY, Wang EY, Huang T. Identification method for microseismic, acoustic emission and electromagnetic radiation interference signals of rock burst based on deep neural networks. Int J Rock Mech Min Sci 2023; 170:105541.

[33] Zhao XL, Huang BX, Cheng QY, Wang CW, Chen SL. Experimental investigation on basic law of rock directional fracturing with static expansive agent controlled by dense linear multi boreholes. J Cent South Univ 2021; 28(8):2499-513.

[34] Sih GC. Strain—energy—density factor applied to mixed mode crack problems. Int J Fract 1974; 10(3):305—21.

[35] Heng S, Yang CH, Zeng YJ, Guo YT, Wang L, Hou ZK. Experimental study on hydraulic fracture geometry of shale. Chinese Journal of Geotechnical Engineering 2014; 36(7):1243—51. in Chinese.

[36] Zhang SC, Mu CM, Feng XH, Ma K, Guo X, Zhang XS. Intelligent dynamic warning method of rockburst risk and level based on recurrent neural network. Rock Mech Rock Eng 2024; 57(5):3509—29.

[37] Ma K, Xie HB, Ren FQ, Chang Y. Rockburst early—warning method based on time series prediction of multiple acoustic emission parameters. Tunn Undergr Space Technol 2024; 153:106060.

[38] Graham CC, Stanchits S, Main IG, Dresen G. Comparison of polarity and moment tensor inversion methods for source analysis of acoustic emission data. Int J Rock Mech Min Sci 2010; 47(1):161-9.

[39] Liu GY, Kang JS, Zhong ZR, Bo W, Fan H, Yang C. Laboratory experiments and 3D DDA numerical simulations on rockfall movement characteristics. Rock Mech Rock Eng 2025; 58(8):9747-69.

[40] Peng C, Cheng YD, Du XT, Liu WR, Xu CM, Sun YL. Study on failure characteristics of pre—crack rock based on digital image correlation (DIC) method and particle flow code (PFC3D). Comput Part Mech 2025; 12(5):3807-24.

[41] Deshmukh S, Raina AK, Murthy VMSR, Trivedi R, Vajre R. Roadheader: a comprehensive review. Tunn Undergr Space Technol 2020; 95:103148.

[42] Zhang KJ, Liu Z, Zhang ZQ. A case study of cutting performance by a transverse cutting head based on three—dimensional particle flow model. KSCE J Civ Eng 2023; 27(5):2248-62.

[43] Bilgin N, Balci C. A review of mechanized tunneling methods. In: Critical Issues in Selecting Conventional and Mechanized Tunnelling Methods. Cham: Springer Nature Switzerland; 2025. p. 93-132.

[44] Chen ZS, Yuan Y, Qin ZH, Wang WM, Li H. The mechanism of crack propagation under dynamic loading stress at different rates. Comput Part Mech 2024; 11(6):2715—26.

[45] Zhou YQ, Sheng Q, Li NN, Fu XD. The relationship between dynamic strength and strain rate and damage to rock materials subjected to dynamic cyclic loading. Geomech Geophys Geo Energy Geo Resour 2021; 7(3):88.

[46] Dong LJ, Liu CZ, Yang LB, Fan FZ, Yuan WY, Hao CL. Acoustic parameters and wave velocity field evolution characteristics in the high—stress region of granite. Measurement 2024; 237:115271.