Numerical investigation of micro-cracking behavior of brittle rock containing a pore-like flaw under uniaxial compression

Abstract

Pore-like flaws, which are commonly encountered in brittle rock, play an important role in the engineering performance of structures constructed in or on rock. Experimental and numerical investigations of micro-cracking mechanism of rock containing a pore-like flaw can enhance our knowledge of rock damage/failure from a microscopic view. In this study, the influences of a two-dimensional circular pore-like flaw with respect to its diameter and position on the strength and micro-cracking behavior of brittle rock under uniaxial compression are numerically investigated. The results reveal that the strength and elastic modulus are significantly affected by the diameter and position in the pore. The uniaxial compressive strength and elastic modulus of the numerical model with a pore diameter of 15.44 mm located in the center of the model are found to decrease by 58.6% and 56.4% respectively when compared with those of the intact model without a pore. As the pore position varies while the porosity remains unchanged, the simulated uniaxial compressive strength and elastic modulus are also found to be generally smaller than those of the intact model without a pore. When a pore-containing numerical model is loaded, the micro-cracks are found to mostly initiate at the top and bottom of the pore, due to the local tensile stress increase. The simulation results of the early-stage micro-cracking process and stress distribution are in a generally good agreement with the analytical solution obtained from the Kirsch equations. The grain-based model used in this study can not only study the crack initiation on the boundary of the pore but also provide a convenient means to analyze and visualize the temporal and spatial micro-cracking process after the crack initiation, which accounts for the variations in the simulated strength and modulus satisfactorily from a micro-cracking view.

Influence of pore‐like flaws on strength and microcracking behavior of crystalline rock

“…In addition, the breakage nature of a contact (ie, tensile or shear) can also be differentiated in the grain‐based model in PFC. The procedures for generating grain‐based model and descriptions of model parameters are not presented in this study, and interested readers can refer to Peng et al 37 or Wong and Peng 25 for more details.…”

“…An in‐depth examination of the microcracking behavior in the complete loading process can greatly enhance our knowledge of rock damage/failure from a microscopic view. In a recent numerical study by Wong and Peng, 25 a grain‐based modeling approach was used to numerically investigate the influences of a single two‐dimensional (2D) circular pore‐like flaw with respect to its diameter and position on the strength and microcracking behavior of rock under uniaxial compression. The study is instrumental in quantifying the influences of the diameter and position of the pore‐like flaw on the test specimen's strength and elastic modulus.…”

“…The grain‐based model cannot only study the crack initiation on the boundary of the pore‐like flaw, but also provide a convenient means to quantitatively analyze and visualize the temporal and spatial microcracking process after the crack initiation, which accounts for the variations in the simulated strength and modulus satisfactorily from a microcracking perspective. The results from Wong and Peng 25 revealed that the strength and microcracking behavior was significantly affected by the diameter and position of a single pore‐like flaw. However, a multiple of pore‐like flaws is more commonly encountered in rocks.…”

Numerical modelling of the crack-pore interaction and damage evolution behaviour of rocklike materials with pre-existing cracks and pores

“…(a) Stresses acting around a circular excavation under a biaxial stress field for Kirsch analytical solution (Kirsch, 1898), and (b) stress distributions on the top and right sides of the opening (modified after Wong and Peng 2020). …”

“… θ=0) of the opening can be simplified from equation (3) as follows: It can be seen from Figure 2(b) and equation (5) that tensile stresses exist in the medium although the far-field stresses are compressive. Since rocks are generally a few times weaker in tension than compression, microcracking generally initiates at the top and bottom of the opening (Wong and Peng, 2020). The results of previous experimental and numerical studies generally show that type of crack initiation and propagation behaviour from a single pore (e.g.…”