Key Takeaways & Executive Findings
- •• The yielding resistance enhancement effect (x) significantly increases yielding force and energy-release capacity compared to unconfined conditions. • In-situ tests under varying rockmass and geostress conditions show yielding forces of 183.4–327.1 kN, confirming the practical applicability. • The analytical theory predicts yielding force with deviations of –12.5% to 6.2%, validating its effectiveness. • Higher geostress and improved rock mechanical properties enhance x, with initial geostress and elastic modulus as critical parameters.
Abstract
To elucidate the yielding performance of compact yielding anchor cables in working state, a yielding mechanical model incorporating extrusion friction and fastening rotation under confining pressure is constructed. The yielding resistance enhancement effect (x) caused by working environment constraints is evaluated through multi-layer composite sleeve hole expansion analysis, forming a theoretical framework for calculating the working yielding force. Laboratory and in-situ pull-out tests are conducted to determine the yielding performance and validate the analytical theory. The main conclusions are: (1) Yielding force and energy-release capacity increase with x, significantly outperforming the unconfined state. (2) In-situ tests under varying rockmass and geostress conditions (F1–F3) determine the yielding force increases to 183.4–290.1, 204.0–290.8, and 235.0–327.1 kN. (3) The slight deviation (–12.5% to 6.2%) between the theoretical and measured yielding force confirms that the analytical theory effectively describes the working yielding performance. (4) x increases with higher geostress and improved rock mechanical properties, with initial geostress (r0) and elastic modulus of surrounding rock (E3) identified as critical parameters.
1. Introduction
Recently, large-scale deformations and rockburst disasters driven by high-ground stress have become increasingly common as underground engineering construction extend into deeper areas. Traditional anchoring systems are often unable to accommodate these large-scale deformations or withstand dynamic impacts, leading to frequent anchor failures and potential safety risks [1,2]. To address this challenge, there is growing demand for large deformation anchor bolts/cables capable of accommodating large-scale deformation while maintaining constant support resistance [3,4]. Among these solutions, structural sliding-type yielding design originating from the Cone bolt have gained widespread use due to their structural stability and reliability advantages, constant resistance yielding, and long energy absorption stroke. Typical examples include the MCB, Yield-Lok bolt, Garford bolt, Roofex bolt, 2S-bolt, and NPR (CRLD) bolt/cable [5,6].
However, conventional structural sliding-type yielding bolts and cables rely solely on rod shank slippage as the yielding mechanism. This mechanism generates yielding force through the resistance created by the internal cone head (yielding body) ploughing inside the external sleeve. Consequently, achieving high-strength constant resistance necessitates a large yielding device, making it challenging to balance the need for timely support (compact size) with high-strength constant resistance performance. To address this limitation, the compact yielding anchor cable was proposed [7]. By integrating extrusion friction and fastening rotation mechanisms, this design provides high-strength constant resistance yielding while maintaining a compact form factor.
The compact yielding anchor cable design, however, introduces a new issue — the influence of the working environment on its yielding mechanical performance. For large-sized yielding bolts and cables, the anchor hole expansion section used to install larger yielding devices can typically only be positioned at the shallow wall of the excavated cavern. As a result, the yielding device typically lacks grouting bond filling between the device and the anchor borehole, which minimizes the impact of the working environment on the yielding process. This environmental influence is negligible.
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WANG Zhenyu, WANG Bo, GUO Xinxin, LI Jinjin, MA Zhenwang (2024). Yielding performance of compact yielding anchor cable in working state: Analytical theory and experimental evaluation of yielding resistance enhancement effect. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2024.12.008
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Frequently Asked Questions
What is the yielding resistance enhancement effect in compact yielding anchor cables?
The yielding resistance enhancement effect (x) refers to the increase in yielding force and energy-release capacity of compact yielding anchor cables when they are constrained by the working environment (e.g., confining pressure from surrounding rock). It is quantified through multi-layer composite sleeve hole expansion analysis and is critical for accurately predicting the working yielding force.
How does the working environment affect the yielding performance of compact yielding anchor cables?
The working environment, including geostress and rock mechanical properties, enhances the yielding resistance of compact yielding anchor cables. Higher geostress and improved rock properties increase the yielding resistance enhancement effect (x), leading to higher yielding forces and energy absorption capacity compared to unconfined conditions.
What are the typical yielding forces observed in in-situ tests?
In-situ tests under varying rockmass and geostress conditions (F1–F3) showed yielding forces increasing to 183.4–290.1 kN, 204.0–290.8 kN, and 235.0–327.1 kN, respectively, demonstrating the significant influence of working conditions.
How accurate is the analytical theory for predicting yielding force?
The analytical theory, which incorporates extrusion friction and fastening rotation under confining pressure, predicts yielding force with a deviation of –12.5% to 6.2% compared to measured values, confirming its effectiveness in describing working yielding performance.
What are the critical parameters influencing the yielding resistance enhancement effect?
The initial geostress (r0) and the elastic modulus of surrounding rock (E3) are identified as critical parameters. Higher geostress and improved rock mechanical properties lead to a greater yielding resistance enhancement effect.
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