Identification of weathered troughs in granites for tunneling at Daya Bay reactor-neutrino experiment site
作者单位：Key Laboratory of Engineering GeomechanicsInstitute of Geology and GeophysicsChinese Academy of Sciences Sichuan Ertan International Engineering Consulting Co.Ltd.
会议名称：《中国科学院地质与地球物理研究所2012年度（第12届）...》
会议日期：2013年
基 金：Supported by the National Natural Science Foundation of China(40972198) the National Key Basic Research and Development Program of China (2010CB732001)
关 键 词：granite Daya Bay reactor-neutrino experiment tunneling weathered trough
摘 要：Weathered trouglis are frequently encountered in granites.They can cause problems to tunneling in the rocks and have to be properly addressed.The structures or spatial shapes of weathered troughs were seldom clarified in the past.In this paper;four weathered troughs are identified by means of geophysical exploration,core drilling,logging,and in-situ stress measurement at Daya Bay reactor-neutrino experiment site in Shenzhen,China.The weathered troughs are exposed on the ground or partially covered by grass and soils,which will threaten the safety of horizontal tunneling at a shallow depth.High electrical resistivity(HER) method is adopted for its feasibility and practicality,in combination with field geological observation,ultrasonic televiewer in boreholes and in-situ stress measurement.By comparing the HER values of completely decomposed to fresh rocks,it is indicated that the HER values of weathered trouglis in natural state are 0.4-100μm,and the in-situ stress is abnormally lower than those at upper and lower layers.Field investigations show that the depths of the four weathered troughs are 30-182 m,with bottom elevation over 10 m.The volume of each weathered trougli is mostly over 1×10 m in inverted conic form.The weathered troughs often occur in various kinds of landforms,such as ridges,gullies or gently dipping dish-like depression areas.Faults and boundaries of different granitic plutons as well as joints govern the formation,locations and strikes of these troughs under development.