甘肃永靖黑方台4·29罗家坡黄土滑坡的特征

2015年4月29日上午,甘肃省永靖县盐锅峡镇黑方台滑坡高频发区的党川村罗家坡同一斜坡处连续发生了2次大规模黄土滑坡,总体积约65×10~4m~3,最大滑距630 m,摧毁14户居民房屋和3家工厂.通过现场详细调查、取样试验、1∶500地形测量、滑坡影像、视频等资料分析,对灌溉引发的罗家坡黄土滑坡的特征、滑动过程、形成机理进行了探讨.结果表明:第1次滑坡经过近2 a变形过程,整体突然失稳,高速远程滑动;第2次滑坡变形时间仅3 h,分块逐步滑动,滑动历时长而过程复杂,总体为低速远程滑动.高陡的地形和强度低、水敏感性强的土体是滑坡发生的基础,黄土台塬区长期农业灌溉是引发因素,大量水体入渗形成了20余米厚的饱和软弱基座,使抗剪强度降低,导致斜坡失稳滑动.黄土滑坡高速远程滑动的主要原因是滑坡剪出口位置高,滑动势能大,释放条件好,剪出口下部陡坡段为主要加速段;前方有开阔的滑动空间且有一定坡度、平缓的滑道;滑体底部饱和软弱黏性土在滑道上持续产生超孔隙水压力、液化等低摩阻效应,是远程滑动的润滑剂.同时,两次滑体间还存在冲击加速和能量传递作用.

Characteristics of the Luojiapo loess landslides at Heifangtai,burst on April 29,2015,in Yongjing County,Gansu Province

In the morning of April 29,2015,two large-scale loess landslides occurred continuously at Luojiapo of Dangchuan Village of Yongjing County,Gansu province. The total volume is about 65×104 m3,with the maxi-mum sliding distance of 630 m,and 14 households and 3 factories destroyed. Based on the analyses of detailed investigation in situ,sampling test,1:500 topographic survey and video data of the landslides,the landslide fea-tures,formation mechanisms and sliding processes are discussed about. It is believed that the Luojiapo Land-slides are loess landslide induced by irrigation. The result show that the first landslide had experienced deforma-tion accumulation for two years,and then collapsed with high speed and long distance. The second landslide had experienced deformation accumulation only 3 hours,sliding block by block,lasting a long time and a complicat-ed process,which was low speed and long distant slide. The basal condition of landslide is high and steep terrain and soil of low strength and water sensitivity;artificial factor is long-term agricultural irrigation in the loess plat-form tableland. When the thickness of saturated soft foundation reaches about 20 m,in case of a large number of water infiltrating in,it will lower the shear strength,and then lead to instability of the loess. The main conditions of loess having high-speed sliding for a long distance are a high position of landslide burst export,a large sliding potential with good release condition and a steep slope at the bottom. It is very important to have an excess pore water pressure caused by saturated soft clay at the bottom of the sliding body,resulting in low friction effect due to liquefaction.