Research on fracture characteristics and support mechanism of shallow buried double-soft composite roof

Abstract

Affected by the geological characteristics of coal bearing strata in western mining areas of China, the double-soft composite roof has low strength and poor integrity, which is prone to induce disasters such as large deformation and roof collapse. Four-point bending tests were conducted on anchored double-layer rock beams with different pre-tightening force and upper/lower rock strength ratios (I/II) based on the digital speckle correlation method (DSCM). The research results indicate that the instability process of anchored roof can be divided into stages of elastic deformation, crack propagation, alternating fracture, and failure collapse. The proportion of crack propagation and alternating fracture processes increased with the increase of pre-tightening force and I/II. The pre-tightening force can suppress the sliding of the upper/lower rock interface, and delay the initiation and propagation of cracks. As I/II increases, the failure mode changes from tensile failure steel strip to shear failure anchor rod. Steel strip can improve the continued bearing effect of anchored roof during crack propagation and alternating fracture processes.

Keywords

double-soft composite roof / anchored composite beams / anchored rock fracture / pre-tightening force / crack propagation

References

[1] ZhaoT-b, ZhangP-f, GuoW-y, et al.. Controlling roof with potential rock burst risk through different pre-crack length: Mechanism and effect research [J]. Journal of Central South University, 2022, 29(11): 3706-3719

[2] ZhangW, GuoW-y, WangZ-qi. Influence of lateral pressure on mechanical behavior of different rock types under biaxial compression [J]. Journal of Central South University, 2022, 29(11): 3695-3705

[3] ChenL-x, GuoW-y, JiangY-j, et al.. Experimental study on influence of lithology on directional propagation law of type-I cracks [J]. Journal of Central South University, 2023, 30(10): 3322-3334

[4] HuP-f, TanchakR, WangQ-s. Developing risk assessment framework for wildfire in the United States - A deep learning approach to safety and sustainability [J]. Journal of Safety and Sustainability, 2024, 1(1): 26-41

[5] ZhaoY-s, FengZ-j. A brief introduction to disaster rock mass mechanics [J]. Geohazard Mechanics, 2023, 1(1): 53-57

[6] WuC. Investigation of foundation theory of safety & security complexity [J]. Journal of Safety and Sustainability, 2024, 1(1): 14-25

[7] FengX-t, YangC-x, KongR, et al.. Excavation-induced deep hard rock fracturing: Methodology and applications [J]. Journal of Rock Mechanics and Geotechnical Engineering, 2022, 14(1): 1-34

[8] ZhangY-l, QiH-n, LiC-q, et al.. Enhancing safety, sustainability, and economics in mining through innovative pillar design: A state-of-the-art review [J]. Journal of Safety and Sustainability, 2024, 1(1): 53-73

[9] ZhangW, ZhangB-l, ZhaoT-b. Study on the law of failure acoustic-thermal signal of weakly cemented fractured rock with different dip angles [J]. Rock Mechanics and Rock Engineering, 2023, 56(6): 4557-4568

[10] PanY-s, WangA-w. Disturbance response instability theory of rock bursts in coal mines and its application [J]. Geohazard Mechanics, 2023, 1(1): 1-17

[11] WuQ-h, YangY, ZhangK-x, et al.. Uniaxial compression mechanical properties and deterioration mechanism of sandstone under different humidity conditions [J]. Journal of Central South University, 2023, 30(12): 4252-4267

[12] DouL-m, SunZ-y, LiX-w, et al.. Detection and targeted control of regional stress field for coal burst prevention [J]. Geohazard Mechanics, 2023, 1(1): 69-76

[13] ZhangC-w, JinZ-x, FengG-r, et al.. Joint load-bearing behaviors and interface failure mechanism of encased coal samples under uniaxial compression [J]. Composite Structures, 2024, 347: 118480

[14] MaQ, LiuX-l, TanY-l, et al.. Experimental study of loading system stiffness effects on mechanical characteristics and kinetic energy calculation of coal specimens [J]. Rock Mechanics and Rock Engineering, 2024, 57(11): 9941-9957

[15] ZhangW, XingM-l, GuoW-y. Study on fracture characteristics of anchored sandstone with precast crack based on double K criterion [J]. International Journal of Solids and Structures, 2023, 275: 112296

[16] ZHANG Wei, WANG Xiu-zhi, XING Ming-lu, et al. Theoretical and experimental study on the mechanical measurement of rock tensile fracture by ring radial compression [J]. Géotechnique, 2024: 1–13. DOI: https://doi.org/10.1680/jgeot.24.01054.

[17] FanD-y, LiuX-s, TanY-l, et al.. Numerical simulation research on response characteristics of surrounding rock for deep super-large section chamber under dynamic and static combined loading condition [J]. Journal of Central South University, 2020, 27(12): 3544-3566

[18] WuQ-h, XieC-l, XieY-s, et al.. Extending application of asymmetric semi-circular bend specimen to investigate mixed mode I/II fracture behavior of granite [J]. Journal of Central South University, 2022, 29(4): 1289-1304

[19] CaoK-w, MaL-q, WuY, et al.. Cyclic fatigue characteristics of rock failure using infrared radiation as precursor to violent failure: Experimental insights from loading and unloading response [J]. Fatigue & Fracture of Engineering Materials & Structures, 2021, 44(2): 584-594

[20] ZhuH-z, WenZ-j, XuL, et al.. Key technology of gob-side entry retained by roof cutting without coal pillar for hard main roof: A typical case study [J]. Journal of Central South University, 2023, 30(12): 4097-4121

[21] HanZ-y, LiD-y, LiX-b. Dynamic mechanical properties and wave propagation of composite rock-mortar specimens based on SHPB tests [J]. International Journal of Mining Science and Technology, 2022, 32(4): 793-806

[22] VazaiosI, VlachopoulosN, DiederichsM S. Assessing fracturing mechanisms and evolution of excavation damaged zone of tunnels in interlocked rock masses at high stresses using a finite-discrete element approach [J]. Journal of Rock Mechanics and Geotechnical Engineering, 2019, 11(4): 701-722

[23] XieH-p, LuJ, LiC-b, et al.. Experimental study on the mechanical and failure behaviors of deep rock subjected to true triaxial stress: A review [J]. International Journal of Mining Science and Technology, 2022, 32(5): 915-950

[24] ChenD-h, ChenH-e, ZhangW, et al.. An analytical solution of equivalent elastic modulus considering confining stress and its variables sensitivity analysis for fractured rock masses [J]. Journal of Rock Mechanics and Geotechnical Engineering, 2022, 14(3): 825-836

[25] FengX-t, ZhangJ-y, YangC-x, et al.. A novel true triaxial test system for microwave-induced fracturing of hard rocks [J]. Journal of Rock Mechanics and Geotechnical Engineering, 2021, 13(5): 961-971

[26] ZhangW, ZhangB-l, GuoW-y. Study on the mechanism of energy evolution and bearing degradation in pre-cracked sandstone under non uniform cyclic loading [J]. Theoretical and Applied Fracture Mechanics, 2024, 132: 104472

[27] WangQ, XinZ-x, JiangB, et al.. Mechanical properties of rocks anchored by constant resistance energy-absorbing material [J]. Journal of Central South University, 2023, 30(10): 3361-3373

[28] ZhangW, ZhaoT-b, ZhangX-t. Stability analysis and deformation control method of swelling soft rock roadway adjacent to chambers [J]. Geomechanics and Geophysics for Geo-Energy and Geo-Resources, 2023, 9(1): 91

[29] AgheshluiH, SedaghatM H, AzizmohammadiS. A comparative study of stress influence on fracture apertures in fragmented rocks [J]. Journal of Rock Mechanics and Geotechnical Engineering, 2019, 11(1): 38-45

[30] AfrasiabianB, EftekhariM. Prediction of mode I fracture toughness of rock using linear multiple regression and gene expression programming [J]. Journal of Rock Mechanics and Geotechnical Engineering, 2022, 14(5): 1421-1432

[31] TaoK, DangW-g, LiY-c. Frictional sliding of infilled planar granite fracture under oscillating normal stress [J]. International Journal of Mining Science and Technology, 2023, 33(6): 687-701

[32] ZhangW, MaQ, LiuX-l, et al.. Study on crack propagation mechanism and acoustic-thermal sensitivity analysis of pre-cracked weakly cemented rock [J]. Theoretical and Applied Fracture Mechanics, 2024, 133: 104619

[33] ZhaoT-b, XingM-l, GuoW-y, et al.. Anchoring effect and energy-absorbing support mechanism of large deformation bolt [J]. Journal of Central South University, 2021, 28(2): 572-581

[34] LiS-c, WangH-t, WangQ, et al.. Failure mechanism of bolting support and high-strength bolt-grouting technology for deep and soft surrounding rock with high stress [J]. Journal of Central South University, 2016, 23(2): 440-448

[35] ZhangW, QiuZ, LiuW-r, et al.. Study on the AE characteristics and energy evolution mechanism of sandstone with different aspect ratios under biaxial compression [J]. Rock Mechanics and Rock Engineering, 2024, 57(11): 9019-9034

RIGHTS & PERMISSIONS

Central South University