The shear dilation and shear contraction evolution of a deeply filled jointed rock mass vary with the structural characteristics of the joint surfaces and the parameters of the filling material, resulting in a more complex change in the shear mechanical behaviour of the anchored jointed rock mass underground. Therefore, shear tests on anchored filled jointed rock masses were conducted under constant normal stiffness (CNS) boundary conditions, considering high initial normal stress and various combinations of roughness (JRC), filling degree (Δ), and filling material strength (σcj). The microstructural evolution characteristics of the filled joint surfaces were analysed by scanning electron microscopy (SEM). On the basis of these results, a calculation method for the peak shear dilation angle under CNS boundary conditions was derived. The research results indicate that when Δ ≤ 0.5, the shear strength of the sample experiences stress hardening, whereas when Δ = 1–1.5, the shear strength evolves from being largely constant to stress softening. Δ plays a controlling role in the normal deformation of the joint. As Δ increases, three evolution patterns are observed: shear dilation, shear dilation followed by shear contraction, and shear contraction. The JRC and σcj affect the degree of shear dilation‒contraction variation in the sample. The failure modes of the filled joint portion undergo three main stages with increasing Δ: the rough asperities are smoothed, the filling material undergoes friction, and the filling material is crushed. From a microscopic perspective, the structure evolves from a loose, porous form to a fragmented, particulate structure. Influenced by the mutual evolution mechanisms of the crushed zone and the stress concentration zone, the shear deformation mode of the anchor rod gradually evolves from an "approximately" tensile‒shear deformation mode at Δ = 0 to a tensile‒bending deformation mode at Δ = 1.5. On this basis, a calculation formula for the peak shear dilation angle of an anchored, filled jointed rock mass under CNS boundary conditions, incorporating the influence factors of JRC, Δ, and σcj, is proposed. Experimental validation and sensitivity analysis of the boundary conditions and the influence parameters are also conducted.Highlights<UnorderedList Mark="Bullet"> <ItemContent> The evolution of the shear displacement curve evolution and shear dilation curve are affected by the degree of filling and exhibit three characteristics after the peak. </ItemContent> <ItemContent> The roughness and filling strength affect the degree of shear dilatancy–shrinkage change in the samples. </ItemContent> <ItemContent> The deformation mode of a soft rock anchor rod changes from the approximate tensile-shear mode to the tensile-bending mode under the influence of the degree of filling. </ItemContent> <ItemContent> A formula for calculating the peak dilatancy angle of anchored filling jointed rock masses under CNS boundary conditions is proposed, which includes the influence factors of joint roughness, filling degree, and filling strength. </ItemContent> </UnorderedList>

Study on the Shear Mechanical Properties of Anchored Jointed Rock Masses Considering the Influence of Filling Parameters Under Constant Normal Stiffness Boundary Conditions

期刊论文
发表日期：

2025年4月21日

查看全文

Heping Wang,
Yang Song,
Weidong Zhang,
Jianhua Zhou,
Jinghan Mao

摘要

The shear dilation and shear contraction evolution of a deeply filled jointed rock mass vary with the structural characteristics of the joint surfaces and the parameters of the filling material, resulting in a more complex change in the shear mechanical behaviour of the anchored jointed rock mass underground. Therefore, shear tests on anchored filled jointed rock masses were conducted under constant normal stiffness (CNS) boundary conditions, considering high initial normal stress and various combinations of roughness (JRC), filling degree (Δ), and filling material strength (σ_cj). The microstructural evolution characteristics of the filled joint surfaces were analysed by scanning electron microscopy (SEM). On the basis of these results, a calculation method for the peak shear dilation angle under CNS boundary conditions was derived. The research results indicate that when Δ ≤ 0.5, the shear strength of the sample experiences stress hardening, whereas when Δ = 1–1.5, the shear strength evolves from being largely constant to stress softening. Δ plays a controlling role in the normal deformation of the joint. As Δ increases, three evolution patterns are observed: shear dilation, shear dilation followed by shear contraction, and shear contraction. The JRC and σ_cj affect the degree of shear dilation‒contraction variation in the sample. The failure modes of the filled joint portion undergo three main stages with increasing Δ: the rough asperities are smoothed, the filling material undergoes friction, and the filling material is crushed. From a microscopic perspective, the structure evolves from a loose, porous form to a fragmented, particulate structure. Influenced by the mutual evolution mechanisms of the crushed zone and the stress concentration zone, the shear deformation mode of the anchor rod gradually evolves from an "approximately" tensile‒shear deformation mode at Δ = 0 to a tensile‒bending deformation mode at Δ = 1.5. On this basis, a calculation formula for the peak shear dilation angle of an anchored, filled jointed rock mass under CNS boundary conditions, incorporating the influence factors of JRC, Δ, and σ_cj, is proposed. Experimental validation and sensitivity analysis of the boundary conditions and the influence parameters are also conducted.

Highlights

The evolution of the shear displacement curve evolution and shear dilation curve are affected by the degree of filling and exhibit three characteristics after the peak.

The roughness and filling strength affect the degree of shear dilatancy–shrinkage change in the samples.

The deformation mode of a soft rock anchor rod changes from the approximate tensile-shear mode to the tensile-bending mode under the influence of the degree of filling.

A formula for calculating the peak dilatancy angle of anchored filling jointed rock masses under CNS boundary conditions is proposed, which includes the influence factors of joint roughness, filling degree, and filling strength.