甘肃舟曲南峪江顶崖古滑坡发育特征与复活机理

Development Characteristics and Reactivation Mechanism of the Jiangdingya Ancient Landslide in the Nanyu Town,Zhouqu County,Gansu Province

江顶崖古滑坡位于甘肃舟曲白龙江左岸,区内地形地貌和地质构造复杂,多高山峡谷且河流纵坡降大,晚第四纪以来强烈活动的坪定—化马断裂带从区内通过,造成地层岩性极为破碎,古滑坡发育,且复活特征明显。在遥感解译和现场调查的基础上,对江顶崖古滑坡的发育特征和复活机理进行分析,认为江顶崖古滑坡堆积体方量为41×106～49×106m3,为在地质历史上形成的巨型古滑坡,位于坪定—化马断裂带及其次级断裂形成的断裂带内。根据滑坡不同位置和坡体结构特征,将江顶崖古滑坡共划分为古滑坡崩塌区、滑坡岩体变形区、古滑坡堆积区等3个大区,以及4个古滑坡复活区等7个区域,坡体内断错陡坎和拉裂缝极为发育。江顶崖古滑坡的中部复活区是主要变形和破坏区,1991年和2018年的复活区均位于该区域内,2018年复活滑坡体体积为480×104～550×104m3,为缓慢滑动的牵引式滑坡。江顶崖古滑坡复活机理复杂,在断裂活动和地震作用下形成的破碎岩土体和斜坡结构特征为滑坡复活提供了内因,强降雨作用增加了坡体自重并弱化了岩土体的力学强度,在暴雨期形成的强烈河流侵蚀作用进一步切割坡脚,从而诱发滑坡的复活;因此,江顶崖古滑坡是在内外动力耦合作用下形成的典型古滑坡复活案例。目前江顶崖古滑坡区域内的4个滑坡复活区仍处于蠕滑状态,在强降雨和河流侵蚀等作用下极可能再次发生复活,并造成堵江和毁坏国道等灾害事件。

The Jiangdingya ancient landslide is located at the left bank of the Bailongjiang River in Zhouqu County,Gansu Province,China,where the terrain and geological structure are very complex,and with alpine gorge and large gradient river.The Pingding-Huama fault zone,which has been active since Late Quaternary,passes through the landslide area.The lithology of the stratum is extremely broken under the impact of active faults,and the ancient landslide is also extremely developed with obvious reactivation characteristics.Based on the remote sensing interpretation and field investigation,this paper analyzed the development characteristics and reactivation mechanism of the Jiangdingya ancient landslide.It is believed that the Jiangdingya ancient landslide accumulation body is nearly 41×10^6 to 49×10^6 m^3,which was formed in the geological history,and the giant ancient landslide is located in the Pingding-Huama active fault zone.According to the different positions of the landslide and the slope structural characteristics,the Jiangdingya ancient landslide is divided into 7 areas,including 3 major areas,i.e.the ancient landslide collapse area,the landslide rock deformation area and the ancient landslide accumulation area,and 4 ancient landslide reactivation zones.The broken fault scarp and cracks are extremely developed in this slope.According to the study,the central reactivation zone of the Jiangdingya ancient landslide is the main deformation and destruction area,and the reactivation zones in 1991 and 2018 are located in this area.The 2018 reactivation landslide volume is about 480×10^4 to 550×10^4 m^3,and it was a slow sliding trailed landslide.The reactivation mechanism of the Jiangdingya ancient landslide is very complex,and the fractured rock mass and slope structure formed under fault activity and earthquake provide internal factors for landslide reactivation.The heavy rainfall increases the self-weight of the slope and weakens the mechanics of the rock and soil.The strong intensity of river erosion formed during the rainstorm period further cuts the slope foot,thus inducing the landslide reactivation.Therefore,it is a typical ancient reactivation landslide formed under the coupling effect of internal and external dynamics factors.At present,the four landslide reactivation zones in the Jiangdingya ancient landslide area are still creeping,and the reactivation will occur again under the action of heavy rainfall and river erosion,and cause disasters such as blocking the river and destroying the national highway.