某涉水崩滑堆积体边坡地震致灾机制综合评估

Comprehensive Assessment on Earthquake DisasterTemporal Deterioration Mechanism of a Reservoir Collapse-slide Slope

弄清高烈度区涉水边坡在地震、库水和人类工程活动综合作用下的坡体扰动劣化机制,是边坡稳定性评价的核心,也是采取有效应对措施的前提。依托某库区历史崩滑堆积体边坡,在搜集得到的勘察设计资料、三峡移民局蓄水及滑坡通报、参建单位往来函件、历史地震资料基础上,结合地面调查和数值计算,采用时空序列分析方法,探讨了该边坡致灾主导因素、坡体扰动程度和稳定性劣化机制,综合评估了工程处置的可行性,所得主要结论如下:(1)工程建设对该库区边坡的扰动和稳定性影响可控;永善和鲁甸两次地震对边坡均有影响,但多达1339次余震的鲁甸地震对该边坡岩土体震松效应影响最大,高水位加剧了震松岩土体的饱和软化,造成该边坡目前整体处于基本稳定-欠稳定状态,坡体前缘处于欠稳定-失稳状态。(2)该边坡坡顶和坡面发育的不良地质和不稳定现象为历史变形迹象,没有继续发展现象;但坡脚临牛栏江到金沙江一线,坡面破坏痕迹新鲜,下部边坡已经严重威胁结构安全。(3)极限平衡分析揭示边坡由勘察阶段的整体稳定,到两次地震作用后的基本稳定-欠稳定状态,达到1.30安全标准所需要加固力为20015~197421 kN/m、加固深度60~180 m、加固范围350~980 m,很难通过工程措施达到加固安全目标。(4)综合评估认为该涉水边坡潜在变形破坏范围深大,无法通过工程加固措施使得边坡满足工程稳定性要求,建议舍弃在建工程。

Ascertaining slope disturbance deterioration mechanism of the reservoir slope in high seismic region under earthquake,reservoir water and human engineering activities actions is the key point of stability estimation and premise of scientific reasonable countermeasures done.Relying on a reservoir collapse-slide slope,its main disaster-causing factor,slope body disturbance and stability deterioration mecha⁃nism are discussed with surface survey and numerical computing combined on the basis of survey and design services,water storage and land⁃slide bulletins of Three Gorges Immigration Bureau,correspondence of participating units and historical earthquake recording.And feasibili⁃ty of engineering disposal is comprehensively estimated,too.Main conclusions are as follows.①Engineering construction exerts little effect on the reservoir slope’s body disturbance and stability.Yongshan earthquake and Ludian earthquake both affect the slope.But Ludian earth⁃quake with 1339 times aftershock does more harm to slope body and remarkable loosening effect produced.High water level enhances shock loosening rock mass saturated softening.The whole slope stability is basic-to-not stable,front local stability being not-to-losing stable.②Deformation traces on slope top and surface are historical ones,which don’t expand.③To meet 1.30 safety standardization needs strength force being 20015~197421 kN/m,reinforcement depth being 60~180 m and reinforcement scope being 350~980 m.It is difficult to meet re⁃inforcement aim by engineering measures.④The reservoir slope is estimated comprehensively.Because it is hard to reinforce by regular engi⁃neering measures,giving up the bridge under construction is suggested.