Characteristics and forming mechanism of the plateau-edge cracks and their significance to loess landslides

黃土滑坡是我國西北地區非常嚴重的地質災害現象,后緣裂縫是黃土滑坡典型特征之一。陜西省涇陽南塬自1976年大面積農業灌溉以來,發生了27處50余起黃土滑坡。研究區塬邊裂縫發育,滑坡密集分布的太平至蔣劉段目前共分布著28條裂縫,總延展長度為1424m。塬邊地形形態控制著裂縫的發育、成因機制,因此,根據裂縫所處塬邊地形形態,將南塬裂縫發育模式分為:'U'模式、'W'模式和'Z'模式。裂縫形成后對塬邊滑坡的發展產生重要影響,使得坡體土體應力狀態接近破壞邊界面,只需較小的孔壓增量和荷載即可誘發滑坡,同時,改變了地表水的入滲途徑,極大地增加了地面灌溉和降雨誘發滑坡的概率。同時,裂縫的形成對于黃土滑坡的演化和群體性分布具有重要的意義。 Loess landslide is the most catastrophic geohazard in Northwestern China. Plateau edge crack is one of the representative characteristics for most loess landslides. Groundwater table in the South Jingyang Plateau, Shaanxi Province has been significantly raised since 1976 and more than 50 landslide events have occurred at 27 sites, resulting in large economic loss and numerous deaths. Based on field survey and measurements of cracks at South Jingyang Plateau, it can be concluded that 28 cracks with a total length of 1424 m were developed at the edge of the study area. Based on the topographic features, the cracks can be classified as 'U' model, 'W' model and 'Z' model. At the initial stage, cracks are caused by the accumulated small strain of the slope soils. The present features of cracks can only reflect the present geological conditions. The forming mechanisms of 'U' model, 'W' model and 'Z' model cracks are, thus, very similar to but not the above mentioned mechanism. Cracks developed change soil stress state and make it to be near the collapse surface, and then a small load or water infiltration can induce landslides. Cracks that can collect surface water and increase the possibility of rain or irrigation induced landslides. Cracks also have important significance to loess Landslides evolution and 'group distribution' characteristics