岩桥破坏全过程分形特征研究

Trace of the specific features of the entire destruction process of the rock bridge

为定量研究边坡岩桥破坏全过程特征,对岩桥试件进行单轴压缩试验,采用盒维数法计算加载过程中裂纹扩展路径的破裂分形维数,基于应力-应变曲线和破裂分形维数量化表征岩桥破裂演化特征,论证了试验结果与实际边坡岩桥破坏过程的相似性;而后,对试件碎屑进行筛分试验,引入破碎分形维数定量描述其破碎特征;最后讨论了这2种分形维数之间的关系。结果表明:1)岩桥试件的应力-应变曲线呈现出"峰后回升"特征;2)破裂演化过程中产生的新生裂纹具有形态上的自相似性,即分形特征,破裂分形维数与应变之间服从双曲线关系;3)岩桥试件破坏后的碎屑尺寸分布具有分形特征,破碎分形维数变化范围在2. 60~2. 67之间;4)数据拟合表明,岩桥试件最终破坏状态的破裂分形维数与破碎分形维数之间呈线性正相关关系,这是因为试件的裂纹萌生、扩展和贯通与破碎特征紧密相关,属于因果关系。

The paper has done a series of uniaxial compression tests on the rock bridge sampling specimens so as to quantitatively trace the specific crack-failure process of the entire slanting rock-built bridge.At the same time,we have also calculated and worked out the fracturing structure dimensions of the fracture gap extension and propagation trend in the loading-bearing process via the box-counting dimension method.The fracturing evolution features of the rock bridge can be quantified and qualified based on the stress-strain curve and the fracturing fractal dimension.And,in comparison of the similarity between the testing results of the paper and the actual failure process of the slope rock bridge,we have done the sieve tests for the fragments of the said specimens through the uniaxial compression tests and made quantitative description by introducing the fragmentation fractal dimension to disclose the fragmentation features.And,finally,a detailed discussion has been made on the relationship between the 2 said fractal dimensions.The results show that the crack is initiated from the tip of the inclined pre-existing flaw primarily.As the stress increases,the second crack is initiated from the tip of the inclined pre-existing flaw and its direction can be controlled by the stress direction.The post-peak rise feature tends to appear in the part of the stress-strain curve.The new cracks,generated in the fracturing process of the rock bridge specimens,may be endowed with morphological self-similarity,that is,the fractal property.In addition,since there exists connection between the variation law of the fracturing fractal dimension and the strain,both of them should obey the rule of the hyperbolic relation.That is to say,the abrupt rise of the fracturing fractal dimension may occur following the post-peak rise.The fragment distribution of the specimens after failure may reveal significant fractal property,with the fragmentation fractal dimension being in the range of 2.60 to 2.67.This may account for the stress concentration effect at the flaw tip.The data fitting also shows that there should exist a positive linear correlation between the fracturing fractal dimension of the final failure state and the fragmentation fractal dimension.This may account for the result that the crack initiation,the crack propagation and the crack coalescence of the rock bridge specimens should all be closely related to the fragmentation nature and the causative relation they should obey.