近断层/远场地震动作用下控制性岩体结构对地下洞室地震稳定性影响研究

 当前地下岩石工程地震响应研究中，缺乏对近断层地震动的影响机制的研究，也较少考虑地下岩石工程赋存环境中的地质结构。采用一种非线性节理本构模型模拟不利地质结构面，结合从NGA-West2数据库中选取的近断层脉冲型、近断层无脉冲型、及远场地震记录，分析近断层地震动对不利地质结构地震破坏现象的影响机制，并讨论、提出不利地质结构的地震动潜在破坏势，最后针对受层间错动带C2切割控制的白鹤滩水电站左岸尾水系统1#尾调室，揭示其在近断层脉冲型、无脉冲型、远场地震动作用下的动力响应与稳定性的差异。初步研究结果表明：(1) 仅有近断层脉冲型地震动才具有较大的速度、位移峰值和反应谱长周期值的特点，而近断层无脉冲型地震动特性与远场地震动近似；(2) 相对于近断层的大幅值，速度脉冲才是导致近断层地震动具有较大破坏能力的根本原因，速度脉冲使得岩体结构面两盘产生不可接受的剪切位移，成为洞室在近断层地震动作用下独特的失稳机制；(3) 对于地下工程中的不利地质结构而言，相比最常用的地震动强度参数PGA，PGV，PGD和PGV/PGA是为更理想的地震动潜在破坏势，且近断层/远场地震动可适用一种破坏势；(4) 提出的潜在破坏势参数在白鹤滩尾水系统1#尾调室的地震响应分析中得到了较好的验证，若受近断层脉冲型地震动的影响，洞室可能处于不稳定状态，可能需要针对性的抗震支护措施。结论可供地下洞室的抗震设计与分析参考。

Seismic response of underground rock cavern dominated by a large geological discontinuity subjected to near-fault and far-field ground motions

Near-fault ground motion mechanisms have seldom been assessed in the seismic studies of underground rock caverns，especially the caverns controlled by large geological discontinuities. A nonlinear joint model was adopted to simulate the unfavorable geological discontinuities. The near-fault pulse-type，near-fault non-pulse-type and far-field ground motion records collected from the NGA-West2 database were used to analyze the influence of near-fault ground motions on unfavorable geological discontinuities. A damage potential index(DPI) was discussed and proposed for unfavorable geological discontinuities. The surge chamber #1 of the Baihetan hydropower plant，which is controlled by the interlayer shear weakness zone(ISWZ) C2，was used as a case study to investigate the differences between the pulse-type near-fault ground motion，non-pulse-type near-fault ground motion and far field ground motion. The significant velocity and displacement and the higher long-period response spectrum were found to associate with the pulse-type near-fault ground motion，while the non-pulse-type near-fault ground motions displayed the similar characteristics as the far field ground motions. The velocity pulse is responsible for the destructive capabilities of near fault ground motions，which may cause the unacceptable sliding along the discontinuity，leading to potential cavern failure. In comparison with several ground motion parameters，PGV was shown to be the most suitable DPI for large geological discontinuities under the earthquake excitation，which was true for both the near-fault and far-field ground motions. PGV was verified to be an effective DPI via the seismic analysis of the Baihetan surge chamber #1. The cavern becomes fragile when subjected to the near-fault ground motions. Therefore，the special seismic reinforcement measures are recommended. These findings may provide a reference for the seismic design of underground caverns.