This study focuses on the mechanical characteristics of the surrounding rock and the energy evolution mechanism during the unloading process of high-stress rock mass excavation. Using the self-developed actual triaxial perturbation unloading test system, actual triaxial unloading tests under different initial stress conditions were conducted, and the failure mechanism was analyzed based on the thin plate failure theory. The results show that (1) The initial third principal stress (σ3) significantly affects the expansion behavior: the larger σ3 is, the stronger the confining pressure constrains the expansion, and the higher the rock sample strength is. The peak stress gradually increases from 165.08 MPa to 229.18 MPa, and the failure direction tends to be concentrated at the free face. During the unloading of the second principal stress (σ2), it shows instantaneous strain rebound followed by stable compression. The first principal stress (σ1) has a significant influence on the transverse strain (ε₂) and has a limited effect on the axial strain (ε₃). (2) Based on the derivation of the deflection equation, the damage range and depth show that the increase of unloading stress leads to the synchronous growth of displacement at the free face and three-dimensional strain, and the rock mass failure degree intensifies. The deflections at the points where the third principal stress reached 5 MPa, 10 MPa, and 20 MPa were 0.189 mm, 0.378 mm, and 0.756 mm, respectively, which were approximately in line with the strain change trend of the third principal stress. The shear fractures are controlled by friction force, mainly developing along the neutral plane or the contact surface between plates, and their scale expands with the increase of unloading stress. (3) The increase of the initial value of σ3 significantly enhances the energy reserve of axial stress, and the dissipation energy of the second and third principal stresses increases simultaneously. Among them, the dissipation energy in the σ3 direction is higher than in the σ2 direction. The increase of the initial value of σ2 enhances the energy in the σ1 direction and induces rebound. After unloading, the dissipation energy in the σ2 and σ3 directions increases, but the dissipation energy in the σ3 direction still dominates. An increase in σ₁ leads to a 40–60% increase in the storage capacity of elastic energy, and the rate of dissipated energy in the σ₃ direction (ΔE/Δσ₁ ≈ 0.8) is higher than that in the σ₂ direction (ΔE/Δσ₁ ≈ 0.5). The research results provide a method for analyzing the mechanical properties of single-sided unloaded rock masses using the thin plate theory, revealing the high-stress rock mass’s mechanical response and energy conversion laws under excavation unloading conditions, and provide theoretical support for related engineering analysis.

Mechanical Behavior and Energy Evolution of Surrounding Rock During Excavation-Induced Unloading in High-Stress Conditions

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发表日期：

2025年8月21日

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Wenzhi Wang,
Wensong Xu,
Guangming Zhao,
Yaoyuan Zhang,
Minjie Qi,
Bin Zhao,
Wei Zhang,
Jiechen Zhao

摘要

This study focuses on the mechanical characteristics of the surrounding rock and the energy evolution mechanism during the unloading process of high-stress rock mass excavation. Using the self-developed actual triaxial perturbation unloading test system, actual triaxial unloading tests under different initial stress conditions were conducted, and the failure mechanism was analyzed based on the thin plate failure theory. The results show that (1) The initial third principal stress (σ₃) significantly affects the expansion behavior: the larger σ₃ is, the stronger the confining pressure constrains the expansion, and the higher the rock sample strength is. The peak stress gradually increases from 165.08 MPa to 229.18 MPa, and the failure direction tends to be concentrated at the free face. During the unloading of the second principal stress (σ₂), it shows instantaneous strain rebound followed by stable compression. The first principal stress (σ₁) has a significant influence on the transverse strain (ε₂) and has a limited effect on the axial strain (ε₃). (2) Based on the derivation of the deflection equation, the damage range and depth show that the increase of unloading stress leads to the synchronous growth of displacement at the free face and three-dimensional strain, and the rock mass failure degree intensifies. The deflections at the points where the third principal stress reached 5 MPa, 10 MPa, and 20 MPa were 0.189 mm, 0.378 mm, and 0.756 mm, respectively, which were approximately in line with the strain change trend of the third principal stress. The shear fractures are controlled by friction force, mainly developing along the neutral plane or the contact surface between plates, and their scale expands with the increase of unloading stress. (3) The increase of the initial value of σ₃ significantly enhances the energy reserve of axial stress, and the dissipation energy of the second and third principal stresses increases simultaneously. Among them, the dissipation energy in the σ₃ direction is higher than in the σ₂ direction. The increase of the initial value of σ₂ enhances the energy in the σ₁ direction and induces rebound. After unloading, the dissipation energy in the σ₂ and σ₃ directions increases, but the dissipation energy in the σ₃ direction still dominates. An increase in σ₁ leads to a 40–60% increase in the storage capacity of elastic energy, and the rate of dissipated energy in the σ₃ direction (ΔE/Δσ₁ ≈ 0.8) is higher than that in the σ₂ direction (ΔE/Δσ₁ ≈ 0.5). The research results provide a method for analyzing the mechanical properties of single-sided unloaded rock masses using the thin plate theory, revealing the high-stress rock mass’s mechanical response and energy conversion laws under excavation unloading conditions, and provide theoretical support for related engineering analysis.