Zundong Yang

Intact deep sandstone cores are scarce, heterogeneous with poorly repeatable, limiting systematic laboratory studies of deep-rock mechanical behavior. This study selected dense sandstone recovered from 1050 m in the Pingdingshan mining area as the prototype system for the development of a targeted-sandstone-constrained screening strategy for simulated deep sandstone. The strategy integrates mineral-composition matching, orthogonal mixture design, mechanical testing, PCA-based comprehensive similarity evaluation, GMM classification, stress–strain curve comparison and fracture-morphology verification. Candidate materials were prepared using a cement–silica-fume matrix with quartz sand, K-feldspar, Na-feldspar, nanoclay and superplasticizer. Results show that the water–binder ratio dominated uniaxial compressive strength, tensile strength and elastic modulus, whereas superplasticizer and nanoclay had secondary effects. The PCA-based index assigned weights of 52.9%, 29.2% and 17.9% to uniaxial compressive strength, elastic modulus and brittleness index, respectively. Among the 25 mixtures sampled, S5 showed the highest mechanical similarity, with a simulation index of 71.65% and a stress–strain curve similarity of 0.958. GMM clustering identified S5 and S10 as the closest high-strength, high-stiffness and high-brittleness group, while S10 better reproduced natural crack geometry. These results indicate that the optimal simulated sandstone depends on the target response and provide a task-oriented route for reproducible simulated deep sandstone.

Nowadays, the depletion of shallow resources drives deeper mining operations. Microwave pre-treatment has shown promise for efficient drilling in deep hard rock. While previous studies have confirmed the feasibility of microwave-assisted crushing of hard rocks and analyzed their structural and mechanical property changes at various scales, the microscopic mechanisms behind the evolution of the macro-mechanical parameters of hard rock remain unclear. This study addresses this knowledge gap. At the microscopic scale, the mineral characteristics and the micromechanical properties of minerals (including interfaces) at different sites before and after microwave irradiation were tested in typical hard granites. At the macroscopic scale, the real-time monitoring of mass and surface heating-rupturing characteristics of granite during microwave irradiation was achieved. Meanwhile, acoustic wave and uniaxial compression tests were conducted to explore the evolution of the macroscopic physical and mechanical parameters of granite before and after microwave irradiation. Variability in the mineral structure and mechanical properties accounts for differences in the uniaxial compression strength of granites. To realize the macro-micro linkage, the micro-mechanical parameters of minerals in different granite sections before and after microwave treatment were upscaled. The upscaling results, obtained using the Mori-Tanaka method, closely matched those from uniaxial compression tests, and the upscaling of mineral micro-mechanical parameters in interior samples was found to accurately predict the weakening of macro-mechanical properties of granite. This study provides insights into how microwave irradiation affects the mechanical properties of granite at a microscopic level, offering a quick and efficient method for assessing microwave weakening in deep hard rock and establishing a theoretical foundation for microwave-assisted mechanical drilling in industrial applications. Document Type: Original article Cited as: Gao, M., Bai, Y., Yang, B., Xie, J., Tang, R., Yang, Z., Zhang, Y. Multi-scale evaluation of mechanical properties of granite under microwave irradiation. Advances in Geo-Energy Research, 2025, 15(1): 30-43. https://doi.org/10.46690/ager.2025.01.04 References Ante, M. A., Lingareddy, M. G., Aminzadeh, F., et al. Nano- and micro-scale deformation behavior of sandstone and shale. Paper ARMA-2018-2055 Presented at 52nd U.S. Rock Mechanics/Geomechanics Symposium, Seattle, Washington, 17-20 June, 2018. Ayatollahi, M., Najafabadi, M. Z., Koloor, S., et al. Mechanical characterization of heterogeneous polycrystalline rocks using nanoindentation method in combination with generalized means method. Journal of Mechanics, 2020, 36(6): 813-823. Brady, B., Brown, E. Rock Mechanics: For Underground Mining. Dordrecht, Netherlands, Springer Dordrecht, 2007. Broz, M. E., Cook, R. F., Whitney, D. L. Microhardness, toughness, and modulus of Mohs scale minerals. American Mineralogist, 2006, 91(1): 135-142. BS EN ISO 14577-1:2002: Metallic materials. Instrumented indentation test for hardness and materials parameters: Test method. British Standards Institute, 2003. Cheng, Y., Li, Z., Cheng, C. Scaling, relationships for indentation measurements. Philosophical Magazine A, 2002, 82(10): 1821-1829. Chen, X., Cheng, Y., Xie, X., et al. Correlation between macro and micro mechanical parameters of marble based on nanoindentation experiment. Rock and Soil Mechanics, 2023, 44(12): 3551-3564. Espinoza, W. F., Zhang, F., Dai, S. Impacts of temperature on the mechanical properties of Longmaxi shale outcrops using instrumented nanoindentation. Geomechanics for Energy and the Environment, 2022, 30: 100348. Hartlieb, P., Grafe, B. Experimental study on microwave assisted hard rock cutting of granite. BHM Berg-und H¨uttenm¨ annische Monatshefte, 2017, 162(2): 77-81. Hay, J. Introduction to instrumented indentation testing. Experimental Techniques, 2009, 33(6): 66-72. Hertz, H. On the contact of elastic solids. Crelle’s Journal, 1881, 92: 156-171. He, X., Xu, Y., Shen, S., et al. Geological environment problems during metro shield tunnelling in Shenzhen, China. Arabian Journal of Geosciences, 2020, 13(2): 87. Hill, R. The elastic behaviour of a crystalline aggregate. Proceedings of the Physical Society Section A, 1952, 65(5): 349-354. the microwave-drill near-field localized heating effect. Journal of Applied Physics, 2005, 97(3): 034909. Ji, S., Wang, Q., Xia, B., et al. Mechanical properties of multiphase materials and rocks: A phenomenological approach using generalized means. Journal of Structural Geology, 2004, 26(8): 1377-1390. Kahraman, S., Canpolat, A. N., Fener, M., et al. The assess ment of the factors affecting the microwave heating of magmatic rocks. Geomechanics and Geophysics for Geo-Energy and Geo-Resources, 2020, 6(4): 66. Law, R. D. Deformation thermometry based on quartz c-axis fabrics and recrystallization microstructures: A review. Journal of structural Geology, 2014, 66: 129-161. Lei, M. Study on the meso-mechanical properties and mecha nism of granite under combined action of hydrochemistry and freeze-thaw cycle based on nanoindentation test. Shaanxi, Xi’an University of Technology, 2022. (in Chinese) Lei, M., Dang, F., Xue, H., et al. Evaluation method of granite multiscale mechanical properties based on nanoindenta tion technology. Geofluids, 2021, 2021: 1-9. Li, C., Wang, D., Kong, L. Mechanical response of the Middle Bakken rocks under triaxial compressive test and nanoindentation. International Journal of Rock Mechanics and Mining Sciences, 2021, 139(7): 104660. Liu, X., Xu, D., Li, S., et al. An insight into the mechanical and fracture characterization of minerals and mineral interfaces in granite using nanoindentation and micro X-Ray computed tomography. Rock Mechanics and Rock Engineering, 2023, 56(5): 3359-3375. Liu, Y., Liu, A., Liu, S., et al. Nano-scale mechanical...

Rock breaking is one of the most basic issues in deep underground engineering. Water plays an important role in the rock response under microwave radiation. Consequently, microwave radiation experiments using red sandstone with different water contents were conducted. The damage characteristics and ultrasonic properties of red sandstone after microwave radiation were primarily investigated, and the representative conclusions were drawn as follows: With the increase in water content, the time of complete formation of the rupture surface of the rock sample gradually decreased, and the decreasing range gradually increased. When the fracture surface is completely formed, the samples with a higher water content have more powdery rock cuttings and less surface roughness. The damage degree of the samples does not increase significantly with the increase in the water content when the sample is radiated at the same time. As the microwave radiation time is increased, the damage degree of the sample will increase significantly. Through the ultrasonic velocity test, it can be suggested that the sample exhibits obvious zonal damage characteristics under the action of a microwave. Generally speaking, it is a very effective means of improving the degree of microwave attenuation of the rock by increasing the water content of the rock mass.