天然岩石由众多大小不均的造岩矿物组成,造岩矿物对微波破岩效果有着重要的影响。为探究矿物粒径分布特征对岩石可照射性的影响规律,选取典型花岗岩样本,量化其矿物粒径的非均匀性指标,通过室内试验考察了粒径分布特征对岩石热响应、裂隙发育、力学性能及纵波传播特性的作用规律。为深入分析粒径分布特征的影响机理,运用多物理场COMSOL分析平台建立数值分析模型,分析微波照射后试样应力场、温度场以及塑性区分布规律与演化发展规律。结果表明:岩石矿物组分的不均匀程度会显著改变岩石内部温度梯度分布,非均匀性越强则表面温升效应越突出,但持续辐照会使升温速率呈现衰减趋势。当矿物粒径分布的非均匀性指标增大时,微波作用诱导的新生裂隙数量显著增加,P波波速降幅增大,试样强度折损率也增高,微波辐照岩石弱化效果更明显;不均匀系数越大的岩石,产生临界应力区面积和塑性区面积占比越多;塑性区率先出现于钾长石与石英的交界处。研究成果有助于阐明矿物颗粒尺寸非均匀分布对微波辐照效应的作用机制。

[Objective] Microwave-assisted rock breaking technology shows promising application potential in hard rock tunneling. The effectiveness of microwave irradiation on rocks is significantly influenced by their microstructure, particularly the mineral particle size distribution. Existing studies mostly focus on single mineral components or simple binary combinations, whereas systematic investigations into how the heterogeneity of complex mineral particle size distributions in natural rocks affects the microwave rock breaking remain limited. This study aims to quantify the heterogeneity of mineral particle size distribution through experiments and numerical simulations, and to reveal its influence mechanisms on the thermal-physical response, damage evolution, and mechanical property degradation of rocks. [Methods] Seven groups of standard granite specimens (Φ50 mm × 100 mm) with different mineral particle size heterogeneity coefficients were selected and subjected to microwave irradiation tests. Surface temperature variations of the specimens during irradiation were monitored, longitudinal wave velocities before and after irradiation were measured, and the peak strengths were obtained through uniaxial compression tests. Image processing techniques were used to extract the surface mineral distributions of the specimens, and quantitative indicators characterizing the heterogeneity of particle size distributions were defined and calculated. Using COMSOL software, a multi-physics numerical model coupling electromagnetic fields, heat conduction, and solid mechanics was established. The model precisely reconstructed the real mineral distributions with different heterogeneity coefficients, and simulated and analyzed the dynamic evolution process of the temperature fields, stress fields, and plastic damage zones of the specimens under microwave irradiation. [Results] (1) Thermal response: under identical irradiation conditions, the heterogeneity of mineral particle size distribution significantly affected the thermal response of the specimens. With the increase of heterogeneity, the temperature rise of the rock became more pronounced. The specimen with the highest heterogeneity (H=0.78) exhibited a final temperature approximately 44 ℃ higher than that of the most homogeneous specimen (H=0.34).(2) Damage and weakening: with increasing heterogeneity coefficient, the number of microwave-induced surface microcracks increased significantly. The reduction in longitudinal wave velocity intensified, with a maximum difference reaching 30%. The uniaxial compressive strength loss rate increased from 11.2% to 29.6%, with a maximum difference of 18.4%. These results indicated that the more heterogeneous the mineral distribution was, the more severe the internal damage induced by microwaves and the more significant the weakening effect on macroscopic mechanical performance became.(3) Mechanism: stronger heterogeneity led to more intense temperature gradients and thermal stress concentrations at the interface between strong microwave-absorbing minerals (such as potassium feldspar) and weak microwave-absorbing minerals (such as quartz). This was because specimens with higher heterogeneity contained larger potassium feldspar particles, which had stronger microwave absorption capacity, resulting in a rapid local temperature rise. Both the area proportion of the critical tensile stress zones (>15 MPa) and the area proportion of the plastic zones increased monotonically with the increase of the heterogeneity coefficient. The plastic zones first appeared at the contact interface between potassium feldspar and quartz and expanded over time. [Conclusion] The heterogeneity of mineral particle size distribution is a key microstructural factor controlling the effectiveness of microwave-assisted rock breaking. The defined quantitative heterogeneity coefficient can effectively predict the outcomes of microwave irradiation: rocks with higher heterogeneity are more likely to experience uneven heat accumulation and large interfacial thermal stresses under microwave irradiation, thereby leading to more extensive microcrack initiation, more significant wave velocity reduction, and more significant strength loss. This study identifies the potassium feldspar-quartz interface as the preferential site for damage initiation.