秦岭北缘仙游寺粘土(膨胀土)的发现及初步研究

首次在秦岭北缘周至县马召镇仙游寺一带发现了中更新世厚层褐色粘土，命名为“仙游寺粘土”。它们是中更新世晚期湿润(半湿热)气候环境下形成的坡面流堆积，其物质来源为秦岭山地表层的褐色古风化壳。室内土工试验结果表明：仙游寺粘土是一种典型的富含膨胀性粘土矿物(伊利石／蒙脱石混层矿物)的膨胀土，是以往渭河盆地没有发现的膨胀土新类型。仙游寺粘土不良的工程特性导致仙游寺周边和108国道秦岭北缘一带的天然斜坡和人工边坡都很不稳定，在强降雨作用下，大量土体滑坡频繁发生。基于野外调查和室内试验测试结果，着重介绍了仙游寺粘土的发育特征、成因时代及其工程地质特性，这不仅有助于北秦岭山地第四纪古气候的恢复及对北秦岭和渭河盆地第四纪以来地质环境演化的认识，而且对于认识秦岭北缘土体滑坡的成灾机理并指导地质灾害的防治具有重要的意义。

THE DISCOVERY AND PRELIMINARY RESEARCH OF XIANYOUSI CLAY(EXPANSIVE CLAY)IN THE NORTH EDGE OF QINLING RANGE

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 surface 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 landslides, as well as to instruct hazard control.