Study on the origin and countermeasure of the casualty loess landfalls in the Northern Shaanxi

In this paper the casualty loess landfall are classified into two types according to their modes of development: tension-sliding loess landfall and collapsed earth cave dwelling .The former is distributed mainly over the base of slope and semi slopes of groove valleys,where some arch cave dwellings were destroyed by it ;the latter is distributed over the side slopes of Yuan(a loess tableland),Liang(an elongated loess mound)and Mao(a around loess mound).Before occurrence of the casualty loess landfall,there are generally some foretastes of landfall(such as the fissures on the slope,frequent fall of earth block,and abnormal phenomena of animal,etc.).In the Northern Shaanxi,casualty loess landfall often occurred during the sixth tenth month of the lunar year,and at night(9:00～12:00 PM)in a day.The casualty loess landfall is produced mainly by following three factors:① The Later Pleistocene loess which has special lithological characters(such as the coarse grains,weak cementation , loose texture,and low strength ,etc.)constitutes the engineering geological condition of this landfall;② Human cut a terrace of building houses in the loess slope,which results in the unstability of side slope and inducement of casualty landfall;③ The precipitation is often a factor of trigger.Therefore,to strengthen scientific management of the house side slope,to cut the top of loess slope and to drain terrene water are the key measures to control casualty loess landfall.