四川九寨沟地震区芦苇海危岩崩塌成因机理分析

Analysis on causation mechanism of dangerous rock collapse in Reed Sea Scenic Area of Jiuzhaigou Seismic Region in Sichuan Province

2017年8月8日,九寨沟地震诱发了景区芦苇海区域约2.7×104 m3危岩体发生崩塌,在2018年汛期该区域又产生约3×104 m3的二次崩塌,损失巨大。目前,崩源区仍有约2×104 m3的危岩体仍悬而未掉,潜在风险高,故需要深入研究芦苇海危岩崩塌的特征和致灾机理。通过现场详查、无人机及GIS等手段,对芦苇海危岩崩塌的基本特征、失稳过程及成因机理有了初步认识。研究发现,芦苇海危岩崩塌失稳历经“坡表局部崩塌-顶部危岩带变形-撞击坡表-碎屑流”四个阶段,平均运动速度达29.94 m/s,崩落块石到达坡脚的概率约为87%。同时,多次失稳主要受内因及外因综合影响,由于斜坡对地震的放大效应,岩体受加速度影响显著,产生震动拉裂或抛射;而震裂的岩土体在后续强降雨的触发下,沿优势结构面向南西侧临空面发生二次崩滑。

On August 8,2017,a 2.7×104 m3 dangerous rock mass collapse occurs in the Reed Sea Scenic Area induced by the Jiuzhaigou Earthquake.During the flood season of 2018,another rock avalanche of 3×104 m3 occurs again along with heavy lo-sses.At present,a dangerous rock mass of about 2×104 m3 still hangs there without falling down with high potential risk in the source area of avalanche,and then the characteristics and disaster-causing mechanism of the dangerous rock mass collapse are necessary to be studied.Through the relevant in situ investigation and by means of UAV and GIS,the basic characteristics,the instability process and the causation mechanism of the dangerous rock mass collapse occurred in the Reed Sea Scenic Area are preliminarily known.The study found out that instability of the dangerous rock mass in the Reed Sea Scenic Area experiences four phases,i.e.local collapse of slope surface-deformation of top dangerous rock belt-impacting slope surface-debris flow,with the mean moving velocity up to 29.94 m/s and the probability of caved rock block reaching slope toe of about 87%.Simutaneously,the multi-times instabilities are mainly under the integrated impact of both the internal and external causes,while the rock mass is significantly impacted by seismic acceleration and then results in vibrating tensile-fracturing or ejecting,moreover,the secondary collapse of the seismically fractured rock and soil mass therein is triggered by the subsequent heavy rainfall from its preferred structural plane to its southwest side free face due to the magnification effect of the slope on earthquake.