高地应力硬脆性围岩开挖损伤区时效性扩展案例分析——特征与机制

A case study of the excavation damage zone expansion time effect in hard brittle country rock under high geostress: characteristics and mechanism

硬脆性围岩在开挖完成后,其强度在高应力的影响下具有明显的时间效应,这导致围岩开挖损伤区的发展也呈现出与时间相关的特征。在岩石强度时效性演化模型的基础上,以锦屏二级水电站试验洞钻孔摄像、声波、变形监测等开挖损伤区实测结果为目标函数,采用正交设计方法、最小二乘支持向量机模型、粒子群优化算法等方法,建立了考虑时间效应的LSSVM-PSO智能反演分析方法,并以锦屏二级水电站试验洞为例,研究了开挖完成后的25 d里,围岩强度在高地应力条件下的时效性演化特征,进而获得这一时段内开挖损伤区扩展过程。研究结果表明:(1)高应力地区,隧洞开挖后,围岩损伤区的主要扩展方向受地应力控制,且最大扩展方向为最小主应力方向,且破坏区(破坏接近度FAI≥2)也集中于该方向;(2)开挖损伤区面积随时间近似呈S形曲线变化,表明开挖损伤区初始发展较为缓慢,随着时间推移呈现线性增加的趋势,最后又逐渐趋于稳定;(3)开挖后第3~10 d为开挖损伤区快速增长阶段。该研究成果对高应力地区硬脆性围岩开挖损伤区时效性演化研究具有指导意义。

The excavation damage zone(EDZ)in hard brittle country rock exhibits noticeable time effect after excavation,as rock strength varies with time caused by the high geostress,which leads to the development of surrounding rock excavation damage zone and shows time-dependent characteristics.The LSSVM-PSO intelligent inversion analysis method considering time effect was established based on the time effect evolution model of rock strength,and measured EDZ data collected in the test tunnel of JinpingⅡHydropower Station,such as borehole monitoring,ultrasonic test and deformation monitoring were used as target functions.The orthogonal design method,least square support vector machine(LSSVM)model and principle of particle swarm optimization algorithm were used to simulate the EDZ’s time effect evolution process between the time excavation ended and 25 days after in JinpingⅡHydropower Station.The study result shows:1)Under high geostress,the principal geostress direction dominates the EDZ expanding,furthermore,the minimum principal stress direction is the main direction for EDZ extending and the failure zone(failure approach index,FAI≥2)also concentrates in this area.2)The area of plastic zone after excavation develops to be"S"shaped curve.The area change of the plastic zone is relatively slow at beginning,then shows a linear increasing tendency and gradually becomes stabilized.3)The plastic zone growth is rapidly increased from 3rd to 10th day after excavation,during which period rock burst is most likely to occur.The research results can provide guidance to the time effect characteristics of EDZ expanding in hard brittle surrounding rock mass under high geostress.