A STUDY ON THE WEAK ZONE TRACING SURVEY OF FILL DAM HYEK KEE KWON1, KEUN JOON RYU2, KANG SUN LEE3, HYUNG JOON PARK4 Investigation of internal defects on fill dams by in-depth inspection is very important and must be carried out. Various several defects such as leakage, settlement, displacement and cracks can be generally occurred in fill dams. In order to investigate defects like these, investigation scope, methods and analysis methods should be properly applied depending on the characteristics and conditions on each dam. In this work, the properties of field investigation methods are analyzed. And with this result, the investigation methods for internal Weak Zones which are not easily defected by external investigation have been studied. Especially, it was possible to defect the weak zones of inside dam body from comparative analysis among Electric Resistivity Search, Borehole Image Processing System(BIPS), Multichannel Analysis of Surface Waves(MASW) and Seismic Tomography etc. As a result, reliable analysis outcomes could be obtained. 1 P.E., Manager, Division of Hydraulic Structures Safety, Korea Infrastructure Safety and Technology Cooperation, Korea, tel : 82 31 910 4112, fax : 82 31 910 4179, e-mail : hkkwon@kistec.or.kr 2 P.E., Head, Division of Hydraulic Structures Safety, Korea Infrastructure Safety and Technology Cooperation, Korea, tel : 82 31 910 4099, fax : 82 31 910 4179, email : ryukj@ kistec.or.kr 3 Senior Manager, Project Engineering Department, Korea Hydro & Nuclear Power Co., Korea, tel : 82 2 3456 1660, fax : 82 2 3456 1669, e-mail : leekanson@khnp.co.kr 4 Engineer, Project Engineering Department, Korea Hydro & Nuclear Power Co., Korea, tel : 82 2 3456 1665, fax : 82 2 3456 1669, e-mail : leekanson@khnp.co.kr