高地应力区大型洞室锚索时效受力特征及长期承载风险分析

Analysis of ageing-stress characteristics and long-term bearing risk of anchor cable for a large cavern in high geo-stress area

深层预应力锚索支护是大型地下洞室围岩稳定控制的主要工程措施。针对高应力区岩体开挖卸荷稳定与锚固支护系统长期承载安全问题,通过对系统锚索安全长期监测成果的深入分析,研究锦屏一级水电站地下厂房系统锚索开挖期和开挖完成后5 a时间的受力特征、时空变化规律,分析锚索预应力随时间演化的时效特征,探讨锚索结构受力影响因素和高应力下长期承载风险,同时辅以数值模拟等手段对锚固系统长期安全性进行综合评价。研究结果表明,与常规洞室表现不同,该地下洞室大部分深层锚索超过设计锁定值,锚索系统负载高,持续增长时间长,时效性十分显著,开挖全部完成后2 a内才逐步趋于收敛,2～5 a基本稳定;锚索长期承载能力影响因素主要有岩体蠕变、锚索初始张拉应力、锚索施工与应力不均匀等;锚索系统长期承载安全是有保障的。

Prestressed anchor cable is the main engineering measure for stability control of surrounding rock mass in large underground caverns. Aiming at the problem of unloading stability of rock mass excavation and long-term bearing safety of anchor support system in high-stress area, the long-term in-situ monitoring results of systematic anchor cable are deeply analysed. In this paper, we investigate the stress characteristics and space-time variation of the anchor cable, and the time-dependent characteristics of the pre-stress of anchor cable in the underground powerhouse system of Jinping I hydropower station located in Southwest of China. The factors influencing the long-term safety of high bearing anchorage cable structure are discussed, and the long-term safety of anchoring system is evaluated with the numerical simulation method. The obtained results show obviously different from them in the conventional cavern. Most of the anchor cables for supporting deep rock mass of this underground cavern exceed the designed locking value, the load of the cable system is high, the continuous growth time becomes long, and the time effect characteristics is greatly significant. The main factors affecting the long-term bearing capacity of anchor cable include the creep of rock mass, initial tension stress of anchor cable, uneven stress of anchor cable. The analysis indicates that the anchorage cable long-term bearing safety is guaranteed.