四川巴塘扎马古滑坡发育特征与复活趋势

Development characteristics and reactivation trend of Zhama ancient landslide in Batang,Sichuan

扎马古滑坡是位于川西巴塘断裂带内的一个大型古滑坡,通过遥感解译、现场调查、钻探等手段,揭示扎马古滑坡体积约2840×10^(4)m^(3)。研究表明,扎马古滑坡局部具有复活特征,在平面上可分为滑坡后壁(Ⅰ)和滑坡体(Ⅱ)2个分区;根据滑坡变形情况将该区划分为中部局部稳定区(Ⅱ_(1))和前缘强变形区(Ⅱ_(2)、Ⅱ_(3)),Ⅱ_(2)和Ⅱ_(3)以坡体前缘的冲沟为界。钻探揭露扎马滑坡体发育两级滑带,其中钻孔ZK1揭露滑带位置为31.8~33.4 m和77.7~81 m,钻孔ZK2揭露滑带位置为46.6~47.6 m和68.2~69.8 m。扎马古滑坡变形受强降雨、地震、人类工程活动等影响,目前以局部变形为主,坡体前缘陡坡部位在汛期发生次级滑动,中部因修建公路开挖诱发多处滑塌,坡体上的侵蚀沟在强降雨作用下发生小规模泥石流。FLAC^(3D)数值模拟表明,在天然工况下扎马古滑坡体后缘发生的位移较大,形成推移式滑坡;在暴雨工况下,滑坡体后缘与坡脚部位均发生剪切变形,易产生贯通滑动面并沿此面发生牵引式滑坡。综合分析认为,该滑坡在强震、强降雨、人类工程活动等影响下,可能沿着滑面发生整体复活。

The Zhama ancient landslide is a large-scale one located in the Batang fault in western Sichuan.The remote sensing interpretation,field investigation and drilling revealed that the Zhama ancient landslide has a volume of about 2840×10^(4) m^(3).The Zhama ancient landslide has local resurrection features,which can be divided into two subregions,the rear collapse(Ⅰ)and slide body(Ⅱ).According to the landslide deformation,the slide body can be divided into the middle part of the local stable region(Ⅱ_(1))and the front of the strong deformation region(Ⅱ_(2),Ⅱ_(3)).Ⅱ_(2) and Ⅱ_(3) are bounded by the gullies at the front edge of the slope.Drilling revealed that two-level slip zones were developed in the Zhama landslide body.The location of two-level slip zones revealed by ZK1 was at 31.8~33.4 m and 77.7~81 m,and that by ZK2 was at 46.6~47.6 m and 68.2~69.8 m.The deformation of the Zhama ancient landslide was affected by heavy rainfall,earthquakes,and human engineering activities.At present,it is mainly local deformation.Secondary sliding occurs in the steep slope part of the front edge of the slope during the flood period.In the middle part,the landslide was induced by road excavation.The erosion ditch on the mountain caused small-scale debris flow under the action of heavy rainfall.The FLAC^(3 D) numerical simulation of the Zhama ancient landslide indicates that under natural conditions,the displacement at the trailing edge of the landslide body is relatively large,causing the formation of moving landslide;under heavy rain conditions,shear deformation occurs on the trailing edge and the toe of the landslide body,and it is easy to produce a through sliding surface and a traction landslide along this surface.It is suggested from comprehensive analysis that under the influence of strong earthquakes,heavy rainfall,and human engineering activities,the landslide may resurrect as a whole along the sliding surface.