分形维数是对岩石裂隙、破碎程度和损伤等细观特征的定量描述,岩石的细观结构往往会对宏观强度特征产生较大的影响。为了研究干湿循环侵水对蚀变花岗岩细观特征的影响,基于电镜扫描(SEM)试验,得到了经历不同干湿循环次数的蚀变花岗岩的细观图像,并通过盒维数法计算得到各岩样的分形维数,建立基于分形维数的细观损伤演化方程;其次,通过室内单轴抗压强度和抗拉强度试验,获得不同干湿循环次数下蚀变花岗岩的力学特性。通过试验数据,得到了干湿循环次数及分形维数分别与岩石强度特性和弹性参数的关系。研究表明:岩石干湿循环次数的增加在宏观上表现为抗拉强度、单轴抗压强度以及弹性模量的减小;在细观上表现为分形维数的增大;泊松比不受此影响。分形维数将岩石细观特征量化、建立了细观和宏观的联系。研究结果可为衡量蚀变花岗岩强度特性的指标提供依据。

Fractal dimension is a quantitative description of mesoscopic features of rock, such as fracture, fragmentation and damage; the meso-structure of rock often has a great impact on the macro-strength characteristics. In this paper, the effect of wet-dry cycles on the meso-scale characteristics of altered granite was investigated. First of all, the meso-scale images of altered granite undergone different dry-wet cycles were obtained through SEM test; the fractal dimension of each rock sample was calculated by box dimension method, and the equation of meso-damage evolution based on fractal dimension was established. Secondly, the mechanical properties of altered granite undergone different dry-wet cycles were acquired by uniaxial compressive strength and tensile strength tests in laboratory. Based on the experimental data, the relations between the number of dry-wet cycles and the strength and elastic parameters of rocks, and the relations between fractal dimension and strength and elastic parameters were obtained respectively. Results showed that the increase of the number of dry-wet cycles of rocks led to the decrease of tensile strength, uniaxial compressive strength and modulus of elasticity in macro-scale, and the increase of fractal dimension at mesoscopic level. Poisson’s ratio was not affected. Fractal dimension quantifies the meso-characteristics of rocks and establishes a meso-and-macro-relationship, which can be used as an indicator of measuring the strength characteristics of altered granite.