Exploration of weakening mechanism of uniaxial compressive strength of deep sandstone under microwave irradiation

Abstract

Traditional mechanical rock breaking method is labor-intensive and low-efficient, which restrictes the development of deep resources and deep space. As a new rock-breakage technology, microwave irradiation is expected to overcome these problems. This study examines the failure characteristics, weakening law, and breakdown mechanism of deep sandstone (depth=1050 m) samples in a microwave field. The macroscopic and microscopic properties were determined via mechanical tests, mesoscopic tests, and numerical simulations. Microwave application at 1000 W for 60 s reduced the uniaxial compressive strength of the sandstone by 50%. Thermal stress of the sandstone was enhanced by uneven expansion of minerals at the microscale. Moreover, the melting of some minerals in the high-temperature environment changed the pore structure, sharply reducing the macroscopic strength. The temperature remained high in the lower midsection of the sample, and the stress was concentrated at the bottom of the sample and along its axis. These results are expected to improve the efficiency of deep rock breaking, provide theoretical and technical support for similar rock-breakage projects, and accelerate advances in deep-Earth science.

Keywords

microwave / sandstone / uniaxial compressive strength / weakening mechanism

References

[1] GaoM-Z, HaoH-C, XueS-N, et al.. Discing behavior and mechanism of cores extracted from Songke-2 well at depths below 4500 m [J]. International Journal of Mining Science and Technology, 2022, 149: 104976

[2] GaoM-Z, ZhangZ-L, YinX-G, et al.. The location optimum and permeability-enhancing effect of a low-level shield rock roadway [J]. Rock Mechanics and Rock Engineering, 2018, 51(9): 2935-2948

[3] GaoM-Z, ZhangJ-G, LiS-W, et al.. Calculating changes in the fractal dimension of surface cracks to quantify how the dynamic loading rate affects rock failure in deep mining [J]. Journal of Central South University, 2020, 27(10): 3013-3024

[4] GaoM-Z, XieJ, GaoY-N, et al.. Mechanical behavior of coal under different mining rates: A case study from laboratory experiments to field testing [J]. International Journal of Mining Science and Technology, 2021, 31(5): 825-841

[5] ZhengY-L, HeL. TBM tunneling in extremely hard and abrasive rocks: Problems, solutions and assisting methods [J]. Journal of Central South University, 2021, 28(2): 454-480

[6] ZhengY-L, ZhangQ-B, ZhaoJ. Challenges and opportunities of using tunnel boring machines in mining [J]. Tunnelling and Underground Space Technology, 2016, 57287-299

[7] AliA Y, BradshawS M. Quantifying damage around grain boundaries in microwave treated ores [J]. Chemical Engineering and Processing: Process Intensification, 2009, 48(1112): 1566-1573

[8] LuG-M, LiY-H, HassaniF, et al.. The influence of microwave irradiation on thermal properties of main rock-forming minerals [J]. Applied Thermal Engineering, 2017, 112: 1523-1532

[9] ZhengY-L, ZhaoX-B, ZhaoQ-H, et al.. Dielectric properties of hard rock minerals and implications for microwave-assisted rock fracturing [J]. Geomechanics and Geophysics for Geo-Energy and Geo-Resources, 2020, 6(1): 1-17

[10] ZhaoQ-H, ZhaoX-B, ZhengY-L, et al.. A review on mineral heating characteristics and rock weakening effect under microwave irradiation [J]. Geological Journal of China Universities, 2020, 26(3): 350-360(in Chinese)

[11] KingmanS W, CorfieldG M, RowsonN A. Effects of microwave radiation upon the mineralogy and magnetic processing of a massive Norwegian ilmenite ore [J]. Magnetic and Electrical Separation, 1999, 9(3): 131-148

[12] KingmanS W, VorsterW, RowsonN A. The influence of mineralogy on microwave assisted grinding [J]. Minerals Engineering, 2000, 13(3): 313-327

[13] LuG-M, FengX-T, LiY-H, et al.. Experimental investigation on the effects of microwave treatment on basalt heating, mechanical strength, and fragmentation [J]. Rock Mechanics and Rock Engineering, 2019, 52(8): 2535-2549

[14] NejatiH, HassaniF, RadziszewskiPExperimental investigation of fracture toughness reduction and fracture development in basalt specimens under microwave illumination [C], 2012, Reston, VA, USA, American Society of Civil Engineers, 325334

[15] LiuJ-Z, ZhuJ-F, ChengJ, et al.. Pore structure and fractal analysis of Ximeng lignite under microwave irradiation [J]. Fuel, 2015, 146: 41-50

[16] LiH, ShiS-L, LinB-Q, et al.. Effects of microwave-assisted pyrolysis on the microstructure of bituminous coals [J]. Energy, 2019, 187: 115986

[17] GaoM-Z, ZhangS, LiJ, et al.. The dynamic failure mechanism of coal and gas outbursts and response mechanism of support structure [J]. Thermal Science, 2019, 23(S3): 867-875

[18] XieJ, GaoM-Z, ZhangR, et al.. Gas flow characteristics of coal samples with different levels of fracture network complexity under triaxial loading and unloading conditions [J]. Journal of Petroleum Science and Engineering, 2020, 195107606

[19] LiY-H, LuG-M, FengX-T, et al.. The influence of heating path on the effect of hard rock fragmentation using microwave assisted method [J]. Chinese Journal of Rock Mechanics and Engineering, 2017, 36(6): 1460-1468(in Chinese)

[20] SatishH, OuelletJ, RaghavanV, et al.. Investigating microwave assisted rock breakage for possible space mining applications [J]. Mining Technology, 2006, 115(1): 34-40

[21] ZHAO Jian, ZHENG Yan-long, ZHANG Qian-bing, et al. Rock fracturing by low power microwave treatment-observations, mechanisms and applications [C]// International Society for Rock Mechanics and Rock Engineering. 2018.

[22] ZhengY L, ZhangQ B, ZhaoJ. Effect of microwave treatment on thermal and ultrasonic properties of gabbro [J]. Applied Thermal Engineering, 2017, 127359-369

[23] PeinsittT, KucharF, HartliebP, et al.. Microwave heating of dry and water saturated basalt, granite and sandstone [J]. International Journal of Mining and Mineral Engineering, 2010, 2(1): 18-29

[24] HartliebP, LeindlM, KucharF, et al.. Damage of basalt induced by microwave irradiation [J]. Minerals Engineering, 2012, 31: 82-89

[25] HassaniF, NekoovaghtP M, GharibN. The influence of microwave irradiation on rocks for microwave-assisted underground excavation [J]. Journal of Rock Mechanics and Geotechnical Engineering, 2016, 8(1): 1-15

[26] HartliebP, KucharF, MoserP, et al.. Reaction of different rock types to low-power (3.2 kW) microwave irradiation in a multimode cavity [J]. Minerals Engineering, 2018, 118: 37-51

[27] HartliebP, GrafeB. Experimental study on microwave assisted hard rock cutting of granite [J]. BHM Berg-Und Hüttenmännische Monatshefte, 2017, 162(2): 77-81

[28] MenzhulinM G, MakhmudovK F. Analysis of the dependence of the break-down point on temperature of microwave heating of loaded heterogeneous materials (rocks) based on the formation of growth of microcracks [J]. Technical Physics, 2019, 64(5): 615-619

[29] GongF-Q, SiX-F, LiX-B, et al.. Dynamic triaxial compression tests on sandstone at high strain rates and low confining pressures with split Hopkinson pressure bar [J]. International Journal of Rock Mechanics and Mining Sciences, 2019, 113: 211-219

[30] LuG-M, FengX-T, LiY-H, et al.. Influence of microwave treatment on mechanical behaviour of compact basalts under different confining pressures [J]. Journal of Rock Mechanics and Geotechnical Engineering, 2020, 12(2): 213-222

[31] MeiselsR, ToiflM, HartliebP, et al.. Microwave propagation and absorption and its thermo-mechanical consequences in heterogeneous rocks [J]. International Journal of Mineral Processing, 2015, 135: 40-51

[32] JonesD A, KingmanS W, WhittlesD N, et al.. The influence of microwave energy delivery method on strength reduction in ore samples [J]. Chemical Engineering and Processing: Process Intensification, 2007, 46(4): 291-299

[33] ToiflM, MeiselsR, HartliebP, et al.. 3D numerical study on microwave induced stresses in inhomogeneous hard rocks [J]. Minerals Engineering, 2016, 90: 29-42

[34] ToiflM, HartliebP, MeiselsR, et al.. Numerical study of the influence of irradiation parameters on the microwave-induced stresses in granite [J]. Minerals Engineering, 2017, 103–104: 78-92

[35] ZhangZ-P, XieH-P, ZhangR, et al.. Deformation damage and energy evolution characteristics of coal at different depths [J]. Rock Mechanics and Rock Engineering, 2019, 52(5): 1491-1503

[36] GongF-Q, ZhaoG-F. Dynamic indirect tensile strength of sandstone under different loading rates [J]. Rock Mechanics and Rock Engineering, 2014, 47(6): 2271-2278

[37] GaoM Z, ZhangR, XieJ, et al.. Field experiments on fracture evolution and correlations between connectivity and abutment pressure under top coal caving conditions [J]. International Journal of Rock Mechanics and Mining Sciences, 2018, 111: 84-93

[38] XieH-PFractal in rock mechanics [M], 1996, Beijing, Science Press(in Chinese)

[39] LiHThermodynamical response of coal and the hydraulic-mechanical coupling mechanism under microwave irradiation [D], 2018, Xuzhou, China University of Mining and Technology(in Chinese)

[40] LinB-Q, LiH, ChenZ-W, et al.. Sensitivity analysis on the microwave heating of coal: A coupled electromagnetic and heat transfer model [J]. Applied Thermal Engineering, 2017, 126: 949-962

[41] WangW-LResearch and simulation analysis of electromagnetic distribution of microwave heating cavity [D], 2015, Changsha, Hunan University(in Chinese)

[42] HartliebP, ToiflM, KucharF, et al.. Thermophysical properties of selected hard rocks and their relation to microwave-assisted comminution [J]. Minerals Engineering, 2016, 91: 34-41

[43] KahramanS, CanpolatA N, FenerM. The influence of microwave treatment on the compressive and tensile strength of igneous rocks [J]. International Journal of Rock Mechanics and Mining Sciences, 2020, 129104303