强震作用下大型古滑坡体变形破坏机理研究

The "5.12" Wenchuan massive earthquake（Ms=8.0）triggerred thousands of collapses and landslides. Especially 114 barrier lakes were formed by the large high-speed landslides blocking rivers in the quake-hit areas. Field investigations indicated that almost all the large scale high-speed landslides were rocky landslides, which didn't slide in the whole scale, just with some shaking cracks and partial collapse taking place at the junctions between the steep and gentle slopes, such as the ancient landslides at the left side of the Zipingpu Dam, Malinyan ancient landslide in the Tangjiashan barrier lake and the Qingtushan ancient landslide in Wenchuan county. Compared with the conventional cognition, the deformation and failure phenomenon of all these landslides showed much difference. Why could the large ancient landslides maintain the general stability in the strong earthquake but not high-speed slide to block rivers?! The preliminary study showed it was closely related to the special landform, geologic texture and sliding surface characteristics of the ancient landslides. The study took the ancient landslide at the left side of the Zipingpu Dam, Malinyan ancient landslide and the Qingtushan ancient landslide as prototype. Through field surveys, dynamics parameter experiments on slip mass and landslide soil, and the physics and numerical simulation, the stability of large ancient landslides under the action of strong earthquakes systemically is studied to reveal the deformation and failure mechanism.

"5.12"汶川大地震（Ms=8.0）触发了数以万计的崩滑地质灾害，尤其在地震核心区内触发形成的大型高速滑坡堵江形成114处堰塞湖，野外调查显示，本次强震触发的大型高速滑坡基本均属岩质滑坡，而位于地震核心区内原有大型古滑坡体未见一例发生整体下滑、只是在局部陡缓交界部位存在震动裂缝或发生局部坍滑，如紫坪铺近坝左岸葫豆坪、北川唐家山堰塞湖库区马铃岩以及汶川县城青土山古滑坡等，均存在上述变形破坏现象，这与常规认识存在很大差异。即强震下为何大型古滑坡体均能保持整体稳定，而未发生一例古滑坡体高速下滑的堵江事件？！初步研究表明与古滑坡体的特殊地形地貌、地质结构、古滑动倾角大小等因素密切相关。本研究以紫坪铺近坝左岸古滑坡、唐家山堰塞湖库区马铃岩古滑坡等为原型，通过现场和室内滑体（含滑带土）动力学参数试验，采用室内物理模拟和数值模拟方法，系统开展大型古滑坡强震作用下动力响应机制研究，以揭示其变形破坏机理。

2008年5月12日发生的汶川地震引发了大量的崩滑地质灾害，通过对强震区诱发的大型高速滑坡堵江现象调查显示，本次强震触发并堵江形成堰塞湖的大型高速滑坡基本均属岩质滑坡，而位于地震核心区内原有大型古滑坡体未见一例发生整体下滑，只是在局部陡缓交界部位产生震动裂缝或局部塌滑，这种古滑坡体在强震作用下保持稳定而不发生整体失稳的现象与之前的常规认识存在较大差异。.通过野外调查、室内试验及数值模拟等手段对汶川地震灾区内北川县唐家山堰塞湖库区马铃岩、都江堰紫平铺库区左岸灯盏坪和汶川县城青土山以及汉源县二蛮山4处代表性古滑坡体，和都（江堰）-汶（川）高速沿线桃关沟、七盘沟等特大泥石流沟域内地震震裂物源等灾害体的地质环境条件、地震稳定性、变形破坏特征、动力响应机理及其影响因素等进行了分析研究：.古滑坡地震稳定性计算结果表明：古滑坡体局部的微地貌，尤其是地形坡度对其地震稳定性有较大影响。总体来看，地震工况下古滑坡体整体稳定性一般均较好，但坡脚前缘浅表层尤其是局部地形陡峭及陡缓交界处的稳定性较差。.动力数值模拟显示，地震力主要影响边坡内部剪应力及剪应变的分布及大小。此外，坡体不同部位加速度及PGA放大系数显示出高程放大效应及临空面放大效应，且局部地形越凸出、坡度越陡，所测的值越大，相应的变形越强烈。.古滑坡体的振动台试验结果显示，坡体表面动力响应明显强于基覆界面处，地震波在地形陡缓转折端的地震放大作用更加显著。当基覆界面倾角和坡面坡度不同时，堆积体边坡的变形破坏模式可总结为三类：①坡面局部滑塌型（基覆界面倾角＜15°）②坡面局部滑塌兼整体蠕滑型（基覆界面倾角为15°～25°）③整体下滑型（基覆界面倾角大于25°）。.对震区泥石流物源启动类型的分析表明，常规松散堆积体受地震影响较小，均以表层坍滑补给，规模有限。而分水岭部位（即单薄山脊部位）的岩质边坡因为震裂松动，反而构成了强震区地震5年以后的最主要补给物源。.总体而言，古滑坡堆积体整体平缓的地形、密实的整体结构、平缓的软滑带及地震波的衰减是使堆积体边坡不同于岩质边坡从而在地震作用下保持整体稳定的主要因素。.研究成果对丰富和完善古滑坡在地震作用下的动力响应及灾害防治具有重要意义。

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