Influence of fracture morphology variation on elastoplastic deformation of unmated rock fractures subject to normal loadings

• Published in: Acta geotechnica Vol. 18; no. 11; pp. 5883 - 5899
• Main Authors: Huang, Lin, Zhao, Cheng, Li, Bo, Chen, Huiguan, Yang, Hongwei, Qian, Yuan
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.11.2023; Springer Nature B.V
• Subjects: Analysis; Asperity; Complex Fluids and Microfluidics; Deformability; Deformation; Deformation effects; Elastic deformation; Elastoplasticity; Engineering; Formability; Foundations; Fractal geometry; Fractal models; Fractals; Fractures; Geoengineering; Geotechnical Engineering & Applied Earth Sciences; Hydraulics; Morphology; Parameter modification; Plastic deformation; Plastics; Regression analysis; Research Paper; Rock; Rock masses; Rocks; Soft and Granular Matter; Soil Science & Conservation; Solid Mechanics; Stability analysis; Stiffness; Contact model; Morphological change; Plastic deformation; Fracture closure; Unmated fracture
• DOI: 10.1007/s11440-023-02024-x
• ISSN: 1861-1125

A large part of fractures found in nature are offset or unmated. The closure behavior of unmated rock fractures under a normal load is critical for the stability analysis of fractured rock masses and the associated coupling process. Local contacted asperities undergone plastic deformation are gradually flattened and dwarfed during a fracture closure, combined with the emergence of new contacts, resulting in the rapid growth of fracture stiffness. The effect of this morphological change on fracture deformability has not been quantitatively characterized, if any. A contact analysis based on the geometrical change of a sphere was put forward to simulate the closure of unmated fractures, validated by fracture closure experiments on three unmated rock fractures. A square-covering fractal method was then employed to characterize the distribution of contacts between two rough surfaces and to quantify fracture morphology variations. A modified exponential model incorporating two new parameters, a fractal dimension and a mixed regime length, was established by regression analysis to quantify the elastoplastic deformation of unmated rock fractures. The results suggest that the elastic and plastic deformation of contacted asperities happens most significantly in the initial loading stage, with a successive growth of the proportion of the plastic deformation in the total deformation. The degradation of fracture morphology leads to a rapid increase in the contact area and fracture stiffness, enhancing the ability of asperities to resist deformation. The modified exponential model yields precise predictions to the experimental data, offering a quick and accurate assessment method for the closure behavior of unmated rock fractures.