Abstract:

For the first time,the authors discover and report a kind of clay distributed around the Xianyou Temple,Mazhao Town of Zhouzhi County,ShaanXi Province in the north edge of Qinling Range,and name it"Xianyousi clay".The characteristics show them belonging to sediments of slope surfaced debris in a moisture or half-heat climate in the late stage of Mid-Pleistocene,which originated from the old weathered crust of the north slope of Qinling Range.Test results indicate that Xianyousi clay is a kind of typical expansive soil containing abundant swelling clay mineral(I/S),which is a new type of expansive soils not discovered by people before.The unfavorable engineering properties of Xianyousi clay lead to slope instability under the condition of hard rainfall,many soil landslides occur frequently near the Xianyou Temple and along the No.108 national highway in the north edge of Qinling Range.Based on field investigation and the results of laboratory experiments,this paper presents the development characteristics,origin and age,as well as the engineering geological properties of Xianyousi clay，which are not only helpful to renew the Quaternary climate and promote the realization of the geological environmental evolution of north Qinling Range and Weihe basin,but also beneficial with theoretical and practical significance to understand the formation mechanisms of soil land slides，as well as to instruct hazard control.

Key words: the north edge of Qinling Range, Mid-Pleistocene clay, expansive clay, engineering geological property, geological environmental evolution