【作者】 张玉敏；

【导师】 盛谦；

【作者基本信息】 中国科学院研究生院（武汉岩土力学研究所） ， 岩土工程， 2010， 博士

【摘要】 随着西部大开发战略的实施,一大批大型水利水电工程已经或即将在我国西部营建。这些大型水利水电工程大部分处在西部地质构造复杂的高山峡谷地区,多数有大型或超大型地下洞室群作为主要水工建筑物。这些大型地下洞室群所处的区域活断层多、规模大、活动强度高,大部分地区地震基本烈度在Ⅶ度或Ⅶ度以上,局部地区强震重复发震周期短。调查表明,在强震作用下地下洞室群等地下结构也常遭破,因此,研究大型地下洞室群在地震荷载作用下的地震响应特征和动力稳定性,是工程设计中亟待解决的问题。本文以大渡河大岗山水电站为依托工程,根据三角级数叠加法合成了基岩场地非平稳人工地震动,结合动态力学特性试验,利用有限差分程序FLAC3D,在研究了大岗山水电站基岩场地地震动传播特性的基础上,对大岗山水电站大型地下洞室群地震响应的数值模型、地震动输入、响应特征、影响因素、损伤区演化规律和分布特征等进行了系统研究,主要研究工作与特点表现在以下几个方面：(1)根据大岗山水电站区域地震地质和近场地震地质情况,确定了对坝址有重大影响的断裂带,划分了潜在震源区,利用烈度衰减关系,计算得到了不同超越概率水平下的坝址场地峰值加速度。选取和大岗山地质条件相近的攀枝花地震记录为样本,研究了其频谱特性,以其地震动卓越频率为基础,利用三角级数叠加法合成了基岩场地非平稳人工地震动。经过基线校正和高频滤波,最终得到了用于数值分析的地震波。(2)对研究区的花岗岩试样进行不同应变率和围压下静态和动态压缩试验,系统分析动弹性模量、泊松比和强度随应变率和围压的变化规律。研究表明,花岗岩的弹性模量随应变速率的增加而增加,并且其增加幅度随围压的提高有减小的趋势。花岗岩的抗压强度随应变速率的增加而增加。编制了弹性模量随应变速率变化数值实现程序。基于大岗山花岗岩静力三轴测试全过程应力-应变曲线和损伤力学分析,发现脆性岩石在不同围压下均以侧向损伤为主,达到临界破坏时,损伤值稳定在0.7-0.8左右,说明了裂纹应变在侧向的发展是导致脆性岩石损伤破坏的主要原因。根据损伤理论建立了岩石动力损伤与静力损伤之间的关系,考虑动态强度与初始弹性模量的率相关性,进而建立了基于静力损伤本构理论的岩石动力损伤本构方程。(3)实际地震记录表明,地震动加速度具有深度衰减效应。本文基于动力有限差分方法研究了高山峡谷地形地震动的传播特性。结果表明,输入地震动向地表传播过程中具有加速度放大作用,换言之,沿地表向地下方向具有衰减效应；峰值加速度对场地深度衰减没有影响；模型底部衰减系数随阻尼比和坡比增加而增大；当地震波的卓越频率接近计算模型自振频率时,场地的衰减程度增大；和实测结果相比,水平峰值加速度随场地深度的衰减趋势大体是相似的；利用FLAC3D软件模拟场地的地震动传播特性是可行的。(4)充分研究了大岗山水电站近场区的地质条件,概化出了大型地下洞室群的数值模型,利用有限差分程序FLAC3D研究了洞室群的地震响应特征,总结了地震作用下围岩加速度、速度、位移和应力的传播特性。研究表明,监测点的加速度时程、速度时程、相对位移时程和应力时程与输入地震动加速度时程包络线形状相似,存在着滞后效应。如果不考虑深度衰减效应,各种工况下主厂房顶拱和底板的水平相对位移偏大39%。(5)系统研究了地应力场、弹性模量、阻尼比、地震动峰值加速度和频谱特性对主厂房拱顶和底板最大水平相对位移的影响。研究表明,地应力和弹性模量对该位移影响非常小；阻尼比有较大影响,随着阻尼比的增大,该位移逐渐降低；峰值加速度有显著影响,随着峰值加速度的增大,该位移呈线性增加；不同频谱特性地震波作用下最大相对位移差别很大,考虑深度衰减效应后,差别有所降低,但仍很显著。初步分析表明,当地震波的卓越频率接近地下洞室群模型自振频率时,主厂房拱顶和底板最大水平相对位移会增大,而当地震波的卓越频率偏离地下洞室群模型自振频率时,该位移则减小。(6)不同频谱地震动作用下,随着输入加速度强度由弱变强,损伤区主要从洞室边墙中部逐步向纵深扩展,在输入地震动强度达到最大值时,损伤区面积也很快达到最大,其后一直保持不变。如果不考虑深度衰减效应,围岩损伤区面积会偏大约32%。初步分析表明,当地震波的卓越频率接近地下洞室群模型自振频率时,围岩损伤区最大面积会增大,而当地震波的卓越频率偏离地下洞室群模型自振频率时,围岩损伤区最大面积则减小。更多还原

【Abstract】 Seismic investigation shows that the underground caverns always suffer some damage under earthquake. The dynamic mechanical tests of granite samples from Dagangshan hydropower station are conducted, and then the seismic propagation in the rock field is simulated by the software FALC3D. Considering the depth attenuation effect, the underground caverns of Dagangshan hydropower station is modeled and simulated to explore its seismic response and damage evolution. The main achievements are summarized as follows:(1)The important fault zones and potential seismic source zones are determined due to seismic geological condition of Dagangshan hydropower station region, and then the peak accelerations under various exceedance probabilities are obtained according to the intensity attenuation relation. Based on the dominant frequency of Panzhihua seismic records, some nonstationary artificial seismic motions are simulated by trigonometric series superposition method.(2)The static and dynamic compression tests of granite samples are conducted to find some changes of dynamic elastic modulus and Passion rate with strain rate and ambient pressure. The test results show that the dynamic elastic modulus of granite sample increases with strain rate, and the compression strength also increases with strain rate. Then the relation between dynamic elastic modulus and strain rate within some given domain are programmed. The full stress-strain of Dagangshan granite under static triaxis test and the damage mechanics analysis show that the brittle rock mainly suffers lateral damage, with damage value 0.7-0.8 near the critical fail. Assuming the linear relation between dynamic damage and static damage, the dynamic damage constitutive function is established.(3)The seismic propagation of mountain& gorge terrain is simulated by FLAC3D. Both the actual seismic records and the numerical simulation shows that the seismic accerlation increases as the earthquake propagates from rock field bottom to top. In other words, the seismic records demonstrate depth attenuation downward and and slope amplification. The attenuation index of model bottom decreases gradually with damping rate and slope ratio; the peak acceleration has no influence on the depth attenuation; the depth attenuation will get intense if the dominant frequency of input seismic motion approaches the natural vibration frequency of the field model. The simulation results basically fit actual seismic records, and it is feasible for FLAC3D to simulate the seismic propagation of rock field.(4) The underground caverns of Dagangshan hydropower station are numerically modeled according to geological conditions, and then the seismic response of the caverns is simulated by FLAC3D. The simulation results show that the acceleration time history, velocity time history, relative displacement time history and stress time history of the monitoring points are similar with and leg behind slightly that of the input seismic motion. The relative horizontal displacement will increase by about 32% without considering the depth attenuation effect.(5)The simulation results show that geostress field and elastic modulus have little influence on the maximum horizontal relative displacement between vault and floor of underground caverns; this maximum displacement increases with damping rate; the peak acceleration has great influence on this maximum displacement, the two indicating a good linear increase relation; seismic motions with different frequency spectra, even considering the depth attenuation, have notable influence on this maximum displacement. The maximum horizontal relative displacement between vault and floor of underground caverns will increase if the dominant frequency of input seismic motion approaches the natural vibration frequency of underground caverns, and vice versa.(6)The damage zone extends deeply from the middle of the cavern wall. The damage zone gets maximum area soon after the input seismic motion reaches the peak acceleration, and then maintain stable subsequently. The maximum damage area will increase by about 32% without considering the depth attenuation effect.The maximum damage area will increase if the dominant frequency of input seismic motion approaches the natural vibration frequency of underground caverns, and vice versa.更多还原