Elastic Modulus and Dynamic Evolution of Fracture in Double-Fractured Sandstone Under Cyclic Loading

doi:10.12068/j.issn.1005-3026.2024.03.008

Abstract

Abstract:

In order to study the changes in elastic modulus and the dynamic evolution of cracks in sandstones with different inclination angles of rock bridges under cyclic loading， uniaxial cyclic loading and unloading tests， along with PFC^2D simulations were carried out on sandstone specimens with rock bridge inclination angles of 15°， 45°， 75°， 90° and 105° when the fissure inclination angle was fixed at 45°. The results show that a significant strengthening of the elastic modulus of sandstone with different fissures due to cyclic loading. There is a correlation between the stress‐strain curve and the instantaneous microcrack evolution curve of specimens obtained from discrete element simulation under cyclic loading. The rock bridge inclination angle has an influence on the damage mode of sandstone， and the dynamic crack evolution in the PFC^2D simulation can reasonably reflect the initiation location and growth direction of cracks in the rock. The damage defined based on the number of microcracks， corresponds well to the damage pattern， with the maximum original damage at a rock bridge inclination angle of 45°.

Key words: double‐fractured sandstone, cyclic loading, elastic modulus, stress‐strain curve, PFC^2D, failure mode, damage variables

CLC Number:

P 642.22

Shu-hong WANG, Xian-peng ZHUANG, Fei WANG, Qian-bai ZHAO. Elastic Modulus and Dynamic Evolution of Fracture in Double-Fractured Sandstone Under Cyclic Loading[J]. Journal of Northeastern University(Natural Science), 2024, 45(3): 361-371.

Figures/Tables 14

Fig.1 Schematic diagram of sandstone specimens and prefabricated fractures

Table 1 Uniaxial cyclic loading and unloading parameters of samples

试件	岩桥倾角β/（°）	裂隙倾角α/（°）	质量/g	体积	密度	峰值强度/MPa
试件	岩桥倾角β/（°）	裂隙倾角α/（°）	质量/g	cm³	g·cm^-3	峰值强度/MPa
Y1	15	45	585.1	248.7	2.35	36.10
Y2	45	45	581.4	245.5	2.37	29.83
Y3	75	45	579.6	243.5	2.38	30.30
Y4	90	45	585.9	249.6	2.35	32.37
Y5	105	45	585.8	250.9	2.33	35.50

Fig.2 Stress?strain curves of specimens

Fig.3 Rock specimen loading path

Table 2 Micro‐parameters in PFC2D

参数	取值
最小颗粒半径/mm	0.5
颗粒粒径比	1.66
颗粒密度/（kg·m^-3）	2 407
颗粒间摩擦系数	0.5
接触模量/GPa	3.5
连接刚度比	1.0
平行接触模量/GPa	3.5
平行黏结刚度比	1.0
法向黏结强度/MPa	14.1
切向黏结强度/MPa	50.0
内摩擦角/（°）	40.0
法向临界阻尼比	0.7

Fig.4 Comparison of loading curves between experiments and simulations

Fig.5 Comparison of rock specimens with PFC2D simulated specimens

Fig.6 Variation law of elastic modulus of different fractured sandstones with the number of cycles

Fig.7 Stress，microcrack number vs. strain evolution curves

Fig.8 Schematic diagram of three main forms of crack growth

Fig.9 Sandstone damage pattern under different rock bridge inclination angles

Fig.10 Crack growth process in sandstone containing prefabricated defects

Fig.11 Macroscopic crack development trend based on PFC2D simulation

Fig.12 Stress?strain curves and damage evolution curves of different sandstone specimens

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