Research On The Development Characteristics And Mechanisms Of Structural Plane Rockburst In Deep-buried Tunnels Under Static And Weak Dynamic Loanding

With the rapid advancement of China’s major water conservancy projects construction strategy,a large number of deeply buried hydraulic tunnels are being constructed in high mountain canyon areas with extremely complex geological conditions.Rockburst,a geological disaster phenomenon characterized by the ejection of rock fragments,is a common occurrence in deep buried tunnels.In recent years,rockbursts induced by small-scale hard structural planes in the surrounding rock,known as structural plane-type rockbursts,have gradually attracted attention.Compared to intact surrounding rock,structural planes weaken the load-bearing capacity of the surrounding rock and alter the stress distribution,leading to greater uncertainty and unpredictability in the occurrence of rockbursts.Currently,the prediction level of structural plane-type rockbursts is seriously inadequate to meet the needs of engineering practice,and the fundamental reason lies in the unclear characteristics and mechanisms of their formation.To address this issue,this paper systematically investigates the formation characteristics and mechanisms of structural plane-type rockbursts.The main research work is as follows:(1)To address the unclear gestation characteristics and mechanisms of rockbursts induced by small-scale rigid structural planes under static loading,biaxial loading tests were conducted on circular borehole red granite specimens containing pre-fabricated structural planes(with different exposure conditions and dip angles)using a true triaxial testing machine.Structural plane-type rockbursts were reproduced in the laboratory,and the rockburst processes of intact rock specimens,specimens with unexposed structural planes,and specimens with exposed structural planes were analyzed.The development characteristics of different types of structural plane-induced rockbursts were summarized.The experimental results showed that structural planes significantly influenced the rockburst process,rockburst crater,and acoustic emission characteristic parameters.The experimental results laid the foundation for analyzing the mechanism of structural plane-type rockbursts,deepened the understanding of the influence of different types of structural planes(with different locations and dip angles)on rockbursts,and provided a basis for the prevention and control of structural planeinduced rockbursts.(2)To address the lack of systematic experimental research on the influence of weak dynamic disturbances on structural plane-type rockbursts,weak dynamic disturbance tests were conducted on circular borehole red granite specimens containing pre-fabricated structural planes of different types(with different exposure conditions and dip angles).The experimental results showed that weak dynamic disturbances significantly influenced the rockburst process,stress conditions for rockburst occurrence,and acoustic emission evolution process.Additionally,it was discovered that weak dynamic disturbances promoted the occurrence of structural plane-type rockbursts,but the promoting effect varied for different types of structural planes.These findings have certain significance for further understanding and preventing the occurrence of structural plane-type rockbursts under the influence of weak dynamic disturbances.(3)To address the unclear energy release mechanism of rockbursts in the surrounding rock mass of tunnels containing single structural planes,numerical simulations were performed using the Local Energy Release Rate(LERR)for physical experiments on structural plane-type rockbursts under static loading and weak dynamic disturbances.By simulating the energy release processes with and without structural planes,under different structural plane exposure conditions and dip angles,and under static and dynamic loading conditions,the energy release characteristics were analyzed,laying the foundation for investigating the mechanism of structural plane-type rockbursts.(4)Addressing the issue that the influence of complex structural planes on rock bursts is not yet fully understood,with the Jinping Ⅱ Hydropower Station as the engineering background,the influence of structural planes on rock bursts under complex conditions was investigated.The simulation results further revealed the gestation characteristics and patterns of rockbursts caused by structural planes under complex geological conditions.Based on the influence law of structural plane-type rockburst,the tendentiousness criterion of structural plane-type rockburst is proposed,which provides scientific basis for reasonable prediction of rockburst grade of deep tunnel.