Abstract
As porous, heterogeneous, and anisotropic material, the microscopic structure of the rock has a significant influence on its mechanical properties. Rare studies were devoted to this area using pore scale modeling and simulations. In this paper, different types of sandstones are imaged using micro-CT technology. The rock porosity is obtained by filtering, binarization, and threshold segmentation. The texture coefficient (TC) and the tortuosity of the rock skeleton are calculated by open source program, where the tortuosity of the rock skeleton is firstly used to characterize the microscopic structure of the rock. Combining with the rock mechanics parameters obtained in the laboratory, the simulation of uniaxial compression is performed on the reconstructed pore scale rock finite element mesh model by ANSYS software. Young’s modulus, compressive strength, yield strength, shear modulus, and other related parameters obtained by numerical simulation are adopted to determine the optimal representative volume element (RVE) size. Moreover, the effects of microscopic structure characteristics on the mechanical properties of the rock are studied quantitatively. The results indicate that the averaged von Mises stress distribution, displacement field, and plastic strain field of rocks show anisotropy and heterogeneity. The stress concentration and the X-shaped conjugate plastic shear zone are investigated. The samples of S1∼S4 reach the elastic limit and enters the plastic yield state, when the strain is about 0.5%. And the critical yield strain of samples S5300-1∼S5400-2 is about 1%. Then, the quantitative relationships between porosity, TC, tortuosity of rock skeleton and rock mechanics parameters of digital rock samples are established and analyzed. The tortuosity of the rock skeleton is highly correlated with the mechanical parameters of the rock, i.e., Young’s modulus (R2 = 0.95), compressive strength (R2 = 0.94), yield strength (R2 = 0.92), and shear modulus (R2 = 0.94), which is believed to be more feasible to reveal the impacts of the microstructure of the rock on its mechanical properties.
Highlights
Rock is a natural porous media with anisotropy, heterogeneity, and discontinuity, which is related to many engineering applications, e.g., resource exploitation, civil construction, and tunnel excavation [1, 2]. e microstructure of the rock has been regarded as one of the important factors for the formation of shear zone, stress concentration, and cracking, which will threaten the safety of geotechnical engineering
In model S5300-1∼S5400-2, there is little difference in porosity, the compressive strength of rock is about 100 MPa, the yield strength is about 60 MPa, and mechanical parameters in each direction are not much different, indicating that the anisotropy of the rock is not obvious
It can be seen from the table that the porosity, texture coefficient (TC), and tortuosity all affect the mechanical parameters of the rock, while the correlation between the tortuosity and the rock mechanical parameters is higher than that of the porosity and TC. us, the tortuosity of the rock skeleton is believed to be more feasible to reveal the impacts of the microstructure of the rock on its mechanical properties
Summary
Rock is a natural porous media with anisotropy, heterogeneity, and discontinuity, which is related to many engineering applications, e.g., resource exploitation, civil construction, and tunnel excavation [1, 2]. e microstructure of the rock has been regarded as one of the important factors for the formation of shear zone, stress concentration, and cracking, which will threaten the safety of geotechnical engineering. Yang et al [26] and Zhu et al [27] used RFPA to simulate the deformation and fracture process of reconstructed rock models in uniaxial compression and Brazil disk test, respectively, and studied the impact of voids and fractures on the rock failure mode. Ju et al [28] combined the CT imaging and X-ray diffraction with physical tests to obtain the pore structure, mineral composition, and mechanical properties of sandstone and established three-dimensional finite element mesh models with different porosity by using Mimics software. Song et al [31, 32] and Wang et al [33] adopted rock microscopic CT imaging and structured the finite element mesh model reconstruction method to establish the finite element model in microscale for sandstone skeleton and pore, and the evolution of pore structure and permeability of the rock was carried out by numerical simulation. The relationship between the porosity, TC and the tortuosity of the rock skeleton, and mechanical parameters are used to quantitatively characterize mechanical properties of the rock
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