Rapid loess flow slides in Heifangtai terrace, Gansu, China
Rapid loess flow slides in Heifangtai terrace, Gansu, China
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中国甘肃黑方台梯田黄土快速滑坡
DOI：
10.1144/qjegh2016-065
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发表时间：
2017-05
影响因子：
1.4
通讯作者：
Wang Gonghui
中科院分区：
文献类型：
--
作者：
Peng Jianbing;Zhang Fanyu;Wang Gonghui
黑方台位于黄河第四阶地，中国甘肃省兰州市以西60公里处（图1a）。梯田面积为13.7平方公里，自20世纪60年代以来，由于刘家峡大坝及其相关的黄河水库的建设，人们从受影响的地区搬迁到这里来。搬迁后，由于农业用地的使用，梯田上的大规模灌溉使地下水水位上升了c。20 m，这是由于在渗透性更强的黄土沉积物下面存在相对不渗透的粘土层（Derbyshire等人，2000; Dijkstra 2000; Zhang等人，2013; Peng等人，2016）。这反过来又导致阶地黄土沉积物中发生了约50次重大滑坡（图1b），总失败次数超过110次（Peng等人，2016）。这些黄土滑坡已造成40多人死亡，100多人受伤。由于与之相关的土壤侵蚀、土地退化和地面沉降的速率增加，它们还导致了严重的生态和环境问题（Zhang et al. 2014）。在已发生的各种滑坡类型中，特别值得注意的是黄土流滑坡，由于其液化敏感性、高流动性和长的运行距离，这是最常见和最具灾难性的破坏类型。流动滑动通常是在陡峭地形区域内以旋转滑动的方式开始的，这些区域在其底部附近包含饱和物质区（即饱和黄土层）。这种饱和区的出现是因为梯田内灌溉或渠道渗漏的水渗透以及黄土沉积物下方相对不透水的粘土的存在，并导致孔隙压力增加，从而导致黄土静态液化。几乎所有最近发生的黄土流滑坡都发生了初始破坏的退化，罗家坡滑坡（图2）就是一个很好的例子。在这种情况下，陡坎的后退发生在初始故障后约2½ h，二次故障产生的碎屑具有比第一次流动滑道明显更大的移动性和跳动距离（图2和图3）。后退也通常以黄土滑塌的形式出现，表现为滑坡陡坎本身的局部破坏（图4和图5）。虽然比黄土流滑的影响小得多，但这些滑塌沉积的物质有时会重新活化，并由于春季活动引起的长期黄土软化而发展成小型黄土流滑（图5）。
The Heifangtai is located on the fourth terrace of the Yellow River, c. 60 km to the west of Lanzhou City, Gansu Province, China (Fig. 1a). The terrace has an area of 13.7 km 2 and, since the 1960s, has been used as farmland by the people relocated from areas affected by the construction of the Liujiaxia Dam and its associated reservoir on the Yellow River. Large-scale irrigation on the terrace resulting from agricultural land use since the relocation has elevated groundwater levels by c. 20 m as a result of the presence of a relatively impermeable clay layer underlying more permeable loess deposits (Derbyshire et al. 2000; Dijkstra 2000; Zhang et al. 2013; Peng et al. 2016). This in turn has led to the occurrence of about 50 major landslides within the loess deposits of the terrace (Fig. 1b), with the total number of failures exceeding 110 (Peng et al. 2016). These loess landslides have caused more than 40 fatalities and have injured over 100 people. They have also resulted in serious ecological and environmental problems owing to the increased rates of soil erosion, land degradation and ground subsidence associated with them (Zhang et al. 2014).Of particular note amongst the various landslide types that have occurred are loess flow slides, which are the most frequent and catastrophic of the failure types owing to their liquefaction sensitivity, high mobility and long runout distances. The flow slides typically initiate as rotational slides within areas of steeper terrain that contain a zone of saturated material (ie a saturated loess layer) near their base. This saturated zone occurs because of water infiltration from irrigation or canal leakage within the terrace and the presence of relatively impermeable clays beneath the loess deposits, and results in increased pore pressures that can cause static liquefaction of the loess. Retrogression of the initial failure has occurred in almost all recent cases of loess flow slides, with the Luojiapo landslide (Fig. 2) providing a good example of this. In this case, retrogression of the scarp occurred approximately 2½ h after the initial failure, with debris from the secondary failure having notably greater mobility and runout distance than the first flow slide (Figs 2 and 3). Retrogression also commonly occurs in the form of loess slumps, which manifest as local failures within the landslide scarp itself (Figs 4 and 5). Although having much less impact than loess flow slides, the material deposited by these slumps sometimes reactivates and develops into a small loess flow slide as a result of long-term loess softening caused by spring activity (Fig. 5).
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