Abstract
The different directions of joints in rock will lead to great differences in damage evolution characteristics. This study utilizes DIP (digital image processing) technology for characterizing the mesostructure of sandstone and combines DIP technology with RFPA2D. The mesoscale fracture mechanics behavior of 7 groups of jointed sandstones with various dip angles was numerically studied, and its reliability was verified through theoretical analysis. According to digital image storage principle and box dimension theory, the box dimension algorithm of rock mesoscale fracture is written in MATLAB, the calculation method of fractal dimension of mesoscale fracture was proposed, and the corresponding relationship between mesoscale fractal dimension and fracture damage degree was established. Studies have shown that compressive strength as well as elastic modulus of sandstone leads to a U-shaped change when joint dip increases. There are a total of six final failure modes of joint samples with different inclination angles. Failure mode and damage degree can be quantified by D (fractal dimension) and ω (mesoscale fracture damage degree), respectively. The larger the ω, the more serious the damage, and the greater the D, the more complex the failure mode. Accumulative AE energy increases exponentially with the increase of loading step, and the growth process can be divided into gentle period, acceleration period, and surge period. The mesoscale fracture damage calculation based on the fractal dimension can be utilized for quantitatively evaluating the spatial distribution characteristics of mesoscale fracture, which provides a new way to study the law of rock damage evolution.
Highlights
Because of the long-term influence of various geological processes, rock mass is cut into each other by different directions and different sizes of structural planes, forming discontinuous bodies with special structures, which leads to the formation of complex mesoscopic structures, and its failure mechanism will be more complicated [1,2,3,4]
In the process of rock failure, deformation problems such as crack initiation, shear zone formation, and stress concentration area distribution are closely related to its internal mesostructured. e heterogeneity of rock and the geometric distribution characteristics of joints with different dip angles have a vital effect on macroscopic failure mode and mesoscale damage evolution process of rock. erefore, studying the macroscopic failure mode and mesoscale damage evolution process has important theoretical significance for revealing the macroscopic nonlinear mechanical behavior and damage mechanical properties of the jointed sandstone fracture process
Compared with the elastic modulus diagram, it is found that the internal stress distribution of the specimen filled with calcite veins is inhomogeneous, at the critical surface between calcite veins and sandstone, and it has higher brightness and significant stress concentration distribution, which indicates that the greater the brightness, the greater the stress. is shows that, in sandstone, the presence of calcite veins and mesostructure’s heterogeneity have an important influence on the distribution of stress
Summary
Because of the long-term influence of various geological processes, rock mass is cut into each other by different directions and different sizes of structural planes, forming discontinuous bodies with special structures, which leads to the formation of complex mesoscopic structures, and its failure mechanism will be more complicated [1,2,3,4]. E heterogeneity of rock and the geometric distribution characteristics of joints with different dip angles have a vital effect on macroscopic failure mode and mesoscale damage evolution process of rock. Zhang et al used physical tests and numerical simulation to study the association among fractal characteristics of cracks’ geometrical distribution along with their mechanical properties after the rock failure in uniaxial compression tests [18]. By properly representing the mesostructure of the rock in the mesoscopic mechanical model, it will be possible to gain a better understanding of the failure mechanism and damage evolution process of the rock For this reason, this paper utilizes DIP technology for characterizing the real mesostructure of sandstone and combines it with the rock fracture process analysis system (RFPA2D) to establish a real mesostructure numerical model considering jointed sandstone with different inclination angles. Erefore, results obtained from the test show that samples are primarily composed of brittle minerals for example quartz
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