为揭示风化花岗岩在循环冲击扰动下的力学退化与损伤演化机制,并构建可连接“微观结构—宏观破坏”的量化表征框架,选取未风化、中风化与强风化花岗岩开展对比研究。首先基于扫描电镜(SEM)图像,结合图像预处理与二值化分割提取微裂隙网络,采用二维盒计数法计算微裂隙分形维数D_f以表征裂隙结构复杂度;随后利用分离式霍普金森压杆(SHPB)开展恒定气压条件下的循环冲击试验。基于动态应力-应变响应与弹性模量退化,定义风化损伤变量D_W及其与冲击累积损伤的耦合表征;同时依据冲击后碎屑粒径分布计算宏观碎屑分形维数D_S,以量化破碎尺度特征。结果表明:随风化程度加剧,矿物分解与次生黏土增多促使微裂隙网络显著发育,D_f由约1.72增至约1.95;在循环冲击作用下,试样峰值承载与动态弹性模量持续劣化,强风化试样退化更为剧烈且更易进入损伤快速增长阶段;分形参数与损伤变量之间具有明确的定量关联,D_f与D_S均随D_W增大呈显著线性增长(R²>0.90),表明微裂隙网络复杂度的分形指标不仅能够表征冲击循环过程中的微观损伤累积,而且能够定量推断宏观破碎尺度与碎屑分布特征,从而实现由微观损伤表征向宏观破坏程度评价的跨尺度联通。

[Objective] To address the lack of a unified quantitative chain linking “microstructure-damage characteristics-macroscopic fragmentation behavior” in weathered granite, this study aims to reveal its mechanical degradation and damage evolution mechanisms under cyclic impact. A dual-scale fractal characterization framework connecting microscopic damage to macroscopic failure is constructed. [Method] Unweathered, moderately weathered, and strongly weathered granite samples from the Meijiang River Irrigation District tunnel project were tested. A dual-scale fractal analysis framework was proposed: micro-crack networks were extracted from SEM images to calculate the micro-crack fractal dimension (D_f) using the 2D box-counting method. Cyclic impact tests were conducted using a Split Hopkinson Pressure Bar (SHPB) under constant air pressure. Based on dynamic stress-strain responses, a weathering damage variable (D_W) coupled with impact cumulative damage was defined. Additionally, the macroscopic debris fractal dimension (D_S) was calculated from post-impact particle size distributions to quantify fragmentation characteristics. [Results] (1) As weathering progressed from unweathered to strongly weathered, mineral decomposition and secondary clay content increased, significantly enhancing micro-crack network complexity. The fractal dimension D_f increased from 1.72 to 1.95, indicating that weathering provides abundant initial defects for subsequent damage evolution. (2) Under fixed impact air pressure loading, specimens with higher weathering degrees exhibited faster peak stress attenuation (the quadratic coefficient decreased from -0.06 to -1.74), increased residual strain, and weakened strain rebound effects. The dynamic elastic modulus deteriorated with increasing impact cycles, with the deterioration amplitude of strongly weathered samples exceeding 50%, reflecting the significant weakening of dynamic fatigue resistance. (3) Weathering damage (D_W) and cumulative damage (D) exhibited coupled nonlinear growth. Unweathered and moderately weathered rocks showed a three-stage evolution of “compaction-stability-sharp increase”, whereas strongly weathered samples almost directly entered the sharp damage increase stage due to extensive secondary cracks. (4) Clear quantitative correlations existed between fractal parameters and damage variables. Both D_f and D_S increased significantly and linearly with increasing D_W (R²>0.90), achieving cross-scale linkage from microscopic damage characterization to macroscopic failure evaluation. [Conclusion] This study establishes a dual-scale fractal characterization framework linking microstructure to macroscopic failure in weathered granite under cyclic impact. The micro-crack fractal dimension (D_f) and debris fractal dimension (D_S) both increase linearly with the weathering damage variable D_W (R²>0.90), confirming that fractal metrics can effectively bridge microscopic damage accumulation and macroscopic fragmentation behavior. Weathering significantly degrades the dynamic fatigue resistance of granite: strongly weathered samples exhibit accelerated peak stress attenuation, elastic modulus deterioration exceeding 50%, and a direct transition to the sharp damage increase stage due to abundant initial defects. These findings provide a quantitative basis for assessing the stability of weathered granite in tunnel engineering under dynamic disturbance and offer a cross-scale evaluation method for rock damage characterization.