Shear characteristics of soft rock-sprayed ECC interface and micro–macro morphology of its shear cross-section under different strain rates and roughness
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2025-08
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Journal Article
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Abstract
Understanding the shear characteristics of the interface between soft rock and sprayed engineering cementitious composites (ECC) is crucial for ensuring the stability of soft rock tunnels subjected to large deformations. In this study, substrates with four different roughness levels were prepared by 3D Scanning, 3D printing and soft rock-similar materials based on the 3D Weierstrass-Mandelbrot fractal function. Shear tests were conducted on the soft rock-sprayed ECC composite specimens under three low strain rates (0.5 × 10−5, 0.5 × 10−4, and 0.5 × 10−3 s−1), and multi-scale morphological features of the shear cross-section were analyzed via 3D scanning, Digital Image Correlation (DIC), and Atomic Force Microscopy (AFM). Results indicated that the shear stress–strain curve comprises four stages: compaction, linear, yielding, and post-peak softening. Shear strength and peak strain increased with interface roughness, while the peak strain decreased with higher strain rates. At the macro-scale, increasing interface roughness elevated the fractal dimension of the shear cross-section, with its curve transitioning from “concave” to “flat” at higher strain rates. The 2D Joint Roughness Coefficient (JRC) at the shear direction center also rose consistently with roughness. At the micro-scale, results revealed that maximum height difference increased with roughness and decreased strain rates, while 3D arithmetic mean deviation (Ra) shifted from “concave” to “convex” with roughness. The 2D JRC exhibited a “Z-shaped” trend but maintained an overall upward correlation with roughness. A quadratic function linked micro- and macro-scale 3D morphology with higher prediction accuracy for elliptical prediction intervals, while a dose–response relationship described their 2D counterparts with lower prediction accuracy. The research findings provide theoretical support for the early-stage support design and analysis of soft rock tunnels under low strain rate conditions.
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Volume
138
Pages / Article No.
104958
Publisher
Elsevier
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Subject
Soft rock tunnel; Sprayed ECC support interface; Roughness; Shear characteristics; Multi-scales