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| Model test study on bearing mechanical properties of anchored gravels |
| MENG Bo1，2，3，JING Hongwen1，WU Jiangyu1，LI Xiaozhao1，3，DONG Jinyuan2，YIN Qian1 |
(1. State Key Laboratory of Intelligent Construction and Healthy Operation and Maintenance of Deep Underground Engineering，China University of Mining and Technology，Xuzhou，Jiangsu 221116，China；2. School of Mechanics and Civil Engineering，China University of Mining and Technology，Xuzhou，Jiangsu 221116，China；3. Yunlong Lake Laboratory of Deep
Underground Science and Engineering，Xuzhou，Jiangsu 221116，China) |
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Abstract To reveal the instability mechanism of deep anchored broken surrounding rock and to explore the internal stress evolution law of the anchored structure under the interaction of support components and gravels，the self-stabilization and reloading model tests of anchored gravels under different pretightening forces were carried out through a self-developed test system. The bearing mechanical properties and deformation failure characteristics of anchored gravels were studied. The influences of the pretightening force on the spatiotemporal responses of internal pressure and bolt anchoring force within structure during the self-stabilization and reloading processes of anchored gravels were analyzed. The mechanisms of self-stabilization and reloading instability of anchored gravels were explored. Based on strengthening the internal force chain network of anchored gravels，a concept of roadway roof fall control was proposed with constant height preload，strong pressure equalizing support，high stiffness and reasonable support density as the core. The results show that the critical pretightening force for self-stabilization of anchored gravels is about 3 N•m. A sudden increase in internal pressure is occurred in the upper-middle part during self-stabilizing process and it spreads outwards to maintain stability. In the lower-middle part，there is a sudden decrease，which is closely related to the redistribution of internal force chain network within the structure. The higher the pretightening force，the more prominent the sudden increase in internal pressure and the less the decrease of the anchoring force. This indicates that high pretightening force is more likely to form a strong force chain network，while low pretightening force result in weak and scattered force chains to damage self-stabilization and loading. During the loading process of anchored gravels，there are frequent and significant stress drops. The larger the pretightening force，the greater the model stress drop，and the maximum loading displacement is generally greater than its peak displacement，and the corresponding load is also lower than the peak load. During the loading process of anchored gravels，the internal pressure behavior is basically consistent with the self-stabilization process，and corresponds to its deformation and failure mode. The dome cavity formed at the center of the lower layer destroys the force chain network，causing the rock mass to spread and fall rapidly along the center of the model to the surrounding areas. The bolt anchoring force decreases continuously with the increase of the loading deformation，and the value of the anchoring force reduction near the central axis of the structure is much greater than that far away from that. High anchoring force is a necessary condition to ensure the force chain network of anchored gravels. The higher the pretightening force，the greater the sudden drop in anchoring force，but after the sudden drop，the structure can still withstand a long time of load.
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2023, Vol. 42 
