Formation mechanism as well as prevention and controlling techniques of loess geo-hazards in irrigated areas: A case study of Heifangtai immigration area in the Three Gorges Reservoir of the Yellow River

Loess is a special type of soil with water sensitivity. The engineering properties of loess change dramatically after soaking with water, which can even cause geo-hazards. Due to irrigation, geo-hazards such as landslides and collapses in Heifangtai are both very severe and typical. Hence Heifangtai has become one of the hot spots for geo-hazard researches and engineering applications. Heifangtai was taken as a study case to reveal the formation mechanism as well as prevention and controlling techniques of loess geo-hazards in irrigation areas. International cooperation researches were carried out in the aspects of hydro-dynamic field and loess engineering geological property responses to irrigation infiltration as well as the consequent loess landslides and loess collapses. The results show that, after 40 years of irrigation, the groundwater table in the center of the plateau has been elevated by 20m with an annual rise of 0.476m. This has led to frequent landslides with annual frequency up to 3 to 5 times. Also, irrigation results in a total collapse of loess of 5.9m. Collapses belonging to both unsaturated loess and loess with a collapse coefficient less than 0.015 reach 2.16m. This has constituted new challenges to the researches on loess collapsibility. The keys to risk control measures of geo-hazards in irrigation areas include changes of irrigation mode, reduction of the recharge of groundwater and implementation of drainage projects to lower groundwater table near the slopes.