大型硬岩地下硐室围岩二次应力场特征弹脆塑性分析

Analysis on secondary stress field characters of hard surrounding rock in large underground caverns by elasto-brittle-plastic constitutive models

结合某水电站硬岩地下厂房开挖,运用FLAC3D软件,对不同地应力环境中大型地下硐室开挖围岩的二次应力场的大小变化、分布特征及其对围岩稳定性的影响进行了三维弹脆塑性数值模拟分析。分析结果表明:①在低地应力环境中,顶拱浅部围岩1σ随开挖逐渐增大,2σ基本不变,3σ在顶拱开挖时迅速降低。而在较高地应力环境中,在顶拱开挖时,应力处于三向迅速卸荷状态;②无论在较高还是低应力环境中,边墙和底板浅部围岩的应力变化路径基本一致,开挖出露时,均处于三向卸荷应力状态;③较高地应力环境中的应力松弛区、集中区及围岩塑性区的分布范围和深度均比较低地应力环境中开挖要大(深);④开挖结束后,围岩的σ1平行于硐室轮廓线,而σ3指向开挖面;⑤硬岩大型地下硐室开挖,由于围岩浅部应力差迅速增大,岩体可能出现脆性破坏,甚至出现岩爆现象。

The paper, according to a hard rock underground house excavated in a hydroelectric station, made 3D elasto-brittle-plastic numerical simulation of variation and distribution characteristics of secondary stress field of large underground caverns excavated surrounding rock in different field stress and its influence to surrounding rock stability by FLAC3D software. The results show：① When in lower field stress, σ1 gradually increased and σ2 was about constant with excavating, but σ3 rapidly decreased when crown was excavated, while in higher field stress in site, secondary field stress in three mayor stress direction all rapidly decreased when crown was excavated in crown shallow surrounding rock; ② Whether in higher or lower field stress, the paths of secondary stress varying in the surrounding rock of the sidewall and soleplate were approximately consistent, both rapidly decreasing in three mayor stress direction when excavating; ③ The range and depth of the stress lax or concentrated zone and plastic zone were larger or deeper in higher stress field than lower; ④ When excavation was ended, σ1 of surrounding rock was parallel with caverns＇ outline and σ3 pointed to excavated surface; ⑤ The surrounding rock possibly appeared brittle failure, indeed rock-burst, because of increasing of σ1 - σ3 when large underground caverns were excavated in hard rock. These researches not only provided data for the research of secondary stress field in underground but also immediate information for informational construction and support.