深切峡谷高位斜坡不同深度地震动响应规律研究

Strong earthquakes often trigger lots of mountainous geohazards, in which large scaled high slope landslides endanger the poverty and life of people. The study reveals the topographical amplification in the slope surface is the main factor for the widespread seismic geohazards, but dynamic process of the seismic wave triggering large scaled landslide is still not clear. There are huge potential safety hazard based on a single PGA of the bedrock at the valley bottom or the PGA multiplied by an empirical coefficient to evaluate high slope seismic stability. In terms of analysis on seismic geological background and the law of strong earthquake migration, select the deep adits in the area where the magnitude 2.0 earthquakes happen frequently, and set the monitoring equipment at different depth in array, monitor the earthquakes around the clock, by the 3D Laser Scanner, measurements of the modulus of elasticity, acoustic wave, pulsation and rockmass structure et al, reveal the relief of the slope, slope structure, the damping ratio et al, set up a database of the slope structure – seismic factors. By statistics of the seismic factor, wave spectrum and energy features each monitoring station of different events, study the real elastic wave transportation process in the complex slope rock mass medium, analyze the energy (amplitude-frequency) evolution in the four dimensional space (time-space). Propose the variation curve of the seismic waves and its function relation of the different depth of the high slope, set up the horizontal and vertical designing seismic spectrum model, advance the further improvement of the code for seismic design of slope.

强震次生山地灾害中危害最大的是大型高位滑坡。已有研究揭示，斜坡表层地形放大效应是大量地震灾害发育的主要原因，但地震波如何触发大型地震滑坡的动力过程并不清楚，目前基于谷底单一基岩峰值加速度来评价西部深切峡谷区高位边坡稳定性具有巨大安全隐患。本研究从分析发震背景及强震迁移规律出发，在2.0级以上地震频发地区选择高位深平硐，在不同深度布设监测台阵，进行全天候自动监测；采用三维激光扫描、岩体弹模测量、声波测试、地脉动测试及岩体结构编录等，揭示边坡地形起伏、坡体结构及阻尼比等特征，建立边坡结构-地震动参数数据库。统计不同事件各测点的地震动参数、波形频谱和能量特征，并系统研究真实复杂斜坡岩体中弹性波传播过程，进而分析能量(幅值-频率)在时间-空间4维坐标系下的变化规律，提出高位斜坡不同深度地震动参数衰减曲线及函数关系式，建立水平与竖直向地震动的设计反应谱模型，推进斜坡抗震加固规范的进一步完善。

强震次生山地灾害中危害最大的是大型高位滑坡。已有研究揭示，斜坡表层地形放大效应是大量地震灾害发育的主要原因，但地震波如何触发大型地震滑坡的动力过程并不清楚，目前基于谷底单一基岩峰值加速度来评价西部深切峡谷区高位边坡稳定性具有巨大安全隐患。本研究从分析发震背景及强震迁移规律出发，在 2.0级以上地震频发地区选择高位深平硐，在不同深度布设监测台阵，进行全天候自动监测，揭示出：（1）基于强震实测与模拟分析，西部深切峡谷地震动响应具体表现为坡表地形放大效应、方向响应（包括主动盘效应），峰值加速度放大倍数为谷底的2-3倍，孤岛状地形可达6-7倍，这是强震表层坡体大面积震裂、崩滑的关键原因；（2）坡体由表及里地震峰值加速度快速衰减，在一定深度加速度衰减变缓并收敛接近谷底背景值（隧洞内部强震破坏较弱正是加速度水平低所致），随谷坡拔河高度的增加或地震强度的增加，峰值加速度衰减、收敛转折点水平深度逐渐加大，可达200m以上（地震巨型滑坡发生提供了动力）；（3）西部深切峡谷强震破坏调查揭示巨型滑坡发育与地震强度呈正比，另一方面高位低约束谷坡因放大效应叠加也可以发生深层大滑坡（斜坡放大效应、深度衰减效应与坡体低约束多叠加产物）；（4）川藏铁路及高速公路川西高位特大桥防震设计建议特别关注高烈度区弱约束斜坡深层（弱卸荷下限）失稳风险。