Hydrogeology Features of Loess Hilly Gully Region in Yan'an

The urban area of Yan'an is located in the valley area of the loess hilly and gully region.The flat and narrow valley zone cannot meet the needs of the urban development,therefore,it is necessary to expand the urban construction to the surrounding loess hilly and gully areas.In the loess hilly and gully area,the construction of the project is bound to be “cutting slope and filling the ditch” or “cutting the gully and filling the ditch”.However,the hydrogeological conditions of this area are relatively complex.The large-scale construction projects, “cutting slope filling ditch” or “cutting the gully and filling the ditch”,are facing with many geotechnical engineering problems caused by the groundwater.The groundwater types,the permeability characteristics of the strata,the hydrogeological structure under the features of various geomorphology,the water bearing systemof groundwater and the runoff and excretion characteristics are summarized and analyzed based on the hydrogeological survey,drilling and test in the loess hilly and gully region of Yan'an.Also,the hydrogeological conceptual model of the loess hilly and gully area is constructed.The results can provide a reference for the “slope cutting and trench filling” or “trench cutting and trench filling” projects in the loess hilly and gully area of Yan'an and similar geological conditions.