Assessing the shear strength of infilled rock joints is fundamental to the analysis of geological hazards and structural reliability. This study conducted direct shear tests on planar infilled joints with infill thicknesses ranging from 0 to 3.5 mm under shear rates of 6-48 mm/min to characterize the influence of shear rate on shear strength. A mathematical expression was subsequently formulated to characterize the relationship among internal friction angle, infilling ratio, and shear rate. Furthermore, an infill deterioration index was introduced to quantitatively evaluate the respective roles of infill and unfilled rock joints in contributing to the overall shear strength, which enabled the formulation of a new predictive model. The results indicate that the shear stress-displacement curve of infilled joints comprises three phases: the stress accumulation phase, the yield phase, and post-peak slip phase. With increases in shear rate and infill thickness, shear strength exhibited a significant nonlinear reduction. Additionally, the internal friction angle displayed a logarithmic-linear dependence on shear rate, whereas the combined effects of shear rate and infill thickness were effectively captured by a second-order polynomial regression equation. The proposed model successfully integrates the mechanical contributions of both unfilled joints and infill, exhibiting excellent agreement with experimental results.
Manuscript Number: IJMST-D-25-00946
Article Type: Full Length Article
Keywords: Infilled rock joints; Direct-shear test; Shear strength; Infilling ratio; Shear rate
Abstract: Assessing the shear strength of infilled rock joints is fundamental to the analysis of geological hazards and structural reliability. This study conducted direct shear tests on planar infilled joints with infill thicknesses ranging from 0 to 3.5 mm under shear rates of 6-48 mm/min to characterize the influence of shear rate on shear strength. A mathematical expression was subsequently formulated to characterize the relationship among internal friction angle, infilling ratio, and shear rate. Furthermore, an infill deterioration index was introduced to quantitatively evaluate the respective roles of infill and unfilled rock joints in contributing to the overall shear strength, which enabled the formulation of a new predictive model. The results indicate that the shear stress-displacement curve of infilled joints comprises three phases: the stress accumulation phase, the yield phase, and post-peak slip phase. With increases in shear rate and infill thickness, shear strength exhibited a significant nonlinear reduction. Additionally, the internal friction angle displayed a logarithmic-linear dependence on shear rate, whereas the combined effects of shear rate and infill thickness were effectively captured by a second-order polynomial regression equation. The proposed model successfully integrates the mechanical contributions of both unfilled joints and infill, exhibiting excellent agreement with experimental results.| Manuscript Number: | IJMST-D-25-00946 |
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| Article Type: | Full Length Article |
| Keywords: | Infilled rock joints; Direct-shear test; Shear strength; Infilling ratio; Shear rate |
| Abstract: | Assessing the shear strength of infilled rock joints is fundamental to the analysis of geological hazards and structural reliability. This study conducted direct shear tests on planar infilled joints with infill thicknesses ranging from 0 to 3.5 mm under shear rates of 6-48 mm/min to characterize the influence of shear rate on shear strength. A mathematical expression was subsequently formulated to characterize the relationship among internal friction angle, infilling ratio, and shear rate. Furthermore, an infill deterioration index was introduced to quantitatively evaluate the respective roles of infill and unfilled rock joints in contributing to the overall shear strength, which enabled the formulation of a new predictive model. The results indicate that the shear stress-displacement curve of infilled joints comprises three phases: the stress accumulation phase, the yield phase, and post-peak slip phase. With increases in shear rate and infill thickness, shear strength exhibited a significant nonlinear reduction. Additionally, the internal friction angle displayed a logarithmic-linear dependence on shear rate, whereas the combined effects of shear rate and infill thickness were effectively captured by a second-order polynomial regression equation. The proposed model successfully integrates the mechanical contributions of both unfilled joints and infill, exhibiting excellent agreement with experimental results. |
Experimental investigation on the shear strength of infilled rock joints
Abstract
Assessing the shear strength of infilled rock joints is fundamental to the analysis of geological hazards and structural reliability. This study conducted direct shear tests on planar infilled joints with infill thicknesses ranging from 0 to 3.5 mm under shear rates of 6-48 mm/min to characterize the influence of shear rate on shear strength. A mathematical expression was subsequently formulated to characterize the relationship among internal friction angle, infilling ratio, and shear rate. Furthermore, an infill deterioration index was introduced to quantitatively evaluate the respective roles of infill and unfilled rock joints in contributing to the overall shear strength, which enabled the formulation of a new predictive model. The results indicate that the shear stress-displacement curve of infilled joints comprises three phases: the stress accumulation phase, the yield phase, and post-peak slip phase. With increases in shear rate and infill thickness, shear strength exhibited a significant nonlinear reduction. Additionally, the internal friction angle displayed a logarithmic-linear dependence on shear rate, whereas the combined effects of shear rate and infill thickness were effectively captured by a second-order polynomial regression equation. The proposed model successfully integrates the mechanical contributions of both unfilled joints and infill, exhibiting excellent agreement with experimental results.
Engineering rock masses inherently develop numerous rock joints across multiple length scales due to complex geological evolution and tectonic activities [1]. Rock joints are often infilled with materials of varying thickness as a result of weathering, erosion, engineering disturbances, and shear displacement between rock walls, forming infilled rock joints [2]. Taking the engineering rock mass of the Baihetan Hydropower Station in China as an example, the rock mass is intersected by ten long and gently dipping interlayer shear weakness zones (ISWZs) labeled from C_(2)C_{2} to C_(10)C_{10} (see Fig. 1a). These typical infilled rock joints consist of a weak interlayer sandwiched between basaltic hanging wall and footwall rocks (Fig. 1b), and are generally simplified in engineering design as planar and uniform weak interfaces by neglecting the spatial variability in infill thickness and the undulating geometry of host rock [3]. When subjected to tectonic or anthropogenic activities, their behavior often becomes the dominant factor controlling rock mass stability [4]. In rock masses containing infilled rock joints, shear slip failure is the predominant failure mode, and this failure pattern is similar to landslides because the poor mechanical properties of infilled rock joints typically control the development of slip surfaces within the rock mass [5]. Therefore, an in-depth investigation into the shear strength characteristics is crucial for advancing the scientific understanding of rock mass stability.