Journal Article

Experimental Study on the Effects of Geometric Parameters of Filled Fractures on the Mechanical Properties and Crack Propagation Mechanisms of Rock Masses

Qin, Yan, Xu, Nengxiong, Zhou, Wenjing, Han, Jian

2023

Overview

The geometric parameters and stress conditions of fractures are the main factors that determine the strength and deformation characteristics of fractured rock masses, and the ultimate instability and failure of fractured rock masses are caused by the extension and penetration of the structural plane. In this study, a series of Φ50 × 100 mm standard cylinder specimens were prepared to simulate brittle rock masses. The uniaxial compressive strength and tensile strength of the specimens were 33 and 2.8 MPa, respectively. Non-persistent fractures with different inclination angles, connectivity rates, openings, spacings, groups, and roughness were prefabricated in the specimens, and the fractures were filled with plasticine. Furthermore, the crack propagation and failure mechanisms of filled fractured rock masses under uniaxial compression (the loading rate is 0.2 MPa/s) were analyzed by a 3D video image correlation system. Comparing the results of this research with those of previous researches, and combining with relevant theoretical analysis, the following conclusions are drawn: (1) the curve of the peak strength reduction coefficient kσ of the specimen with the fracture inclination angle α is roughly V-shaped, and being the smallest when the fracture inclination angle α is 45°; the reduction coefficient k is monotonically decreasing with the three groups of fracture geometric parameters of spacing b, connectivity rate μ, and opening d, and the peak strength reduction coefficient kσ of the specimen is typically smaller than the elastic modulus reduction coefficient kE. (2) The post-peak stress–strain curve of the specimen with filled fractures is relatively slow, and the plasticity is obviously enhanced. The geometric parameters of the fractures are important factors affecting the change of the mechanical properties of the specimen. The influence degree of different fractures geometric parameters on rock masses mechanical properties is as follows: fracture sets > spacing > connectivity rate > inclination angle > opening > roughness. (3) Due to the concentration of stress, cracks first initiate from the fracture tips, then propagate parallel to the loading direction, and ultimately coalesce between the fractures and the specimen surface. During the failure process of the specimens, four types of cracks were observed: tensile cracks, shear cracks, wing cracks, and reverse wing cracks, with wing cracks dominating crack propagation. (4) Compared with the specimens with unfilled fractures, the stress concentration at the filled fractures was reduced, and more microcracks with higher dispersion developed around the filled fracture.HighlightsThe variation mechanism of the mechanical parameter reduction coefficient of a filled fractured rock mass is studied;The influence of different joint geometric parameters on the mechanical properties of a filled fractured rock mass is investigated;The crack propagation of a filled fractured rock mass is observed under different joint geometric parameters and the failure mechanism is analyzed.

• Publisher: Springer Nature B.V
• Subject: Coefficient of variation / Compression / Compressive strength / Connectivity / Crack propagation / Cracking (fracturing) / Cracks / Deformation / Failure analysis / Failure mechanisms / Fractures / Inclination angle / Load distribution / Loading rate / Mechanical properties / Microcracks / Modulus of elasticity / Parameters / Plasticine / Propagation / Reduction / Rock / Rock masses / Rocks / Roughness / Stress concentration / Stress propagation / Stress-strain curves / Stress-strain relations / Tensile strength / Theoretical analysis / Wings