Shear Behavior and Bolt Deformation of Infilled Rock Joints Under the Combined Effects of Roughness, Infill Thickness, and Initial Mixing Water Content

To investigate the shear behavior and anchoring response of bolted infilled rock joints under the combined effects of joint roughness, infill thickness, and initial mixing water content, rock-like specimens with joint roughness coefficients (JRC = 2.8–14.5), infill thicknesses (t = 0–6 mm), and initial mixing water contents (λ = 30–50%) were fabricated by three-dimensional (3D) printing and tested in direct shear under a constant normal stress of 4 MPa to a terminal shear displacement of 7 mm. Within the tested ranges, JRC generally produced the largest percentage variations in the evaluated shear-strength parameters. Increasing JRC enhanced peak shear strength and normal displacement, shifted failure from surface abrasion to asperity shearing, and intensified infill fragmentation. Under unfilled conditions, bolting increased the peak shear strength by 15.6–39.7% and the system-level apparent shear work by 14.3–28.9%. Increasing infill thickness weakened shear resistance and suppressed dilation; at λ = 30%, increasing t from 0 to 6 mm reduced peak shear strength by 17.3–28.2%. Higher initial mixing water content reduced strength when the infill was thick. Based on the overall percentage variation ranges, the apparent influence on the evaluated shear-strength parameters could be broadly ranked as JRC > infill thickness > initial mixing water content within the tested parameter space; this ranking represents a comparative assessment rather than a statistical significance test or a universal ordering. Rock bolts exhibited S-shaped deformation with two plastic hinges, whose spacing increased with JRC and infill thickness. These findings provide experimental insight into the shear behavior and reinforcement response of bolted infilled discontinuities.