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RISS 인기검색어
- 검색키워드
- 저자 : Tsokas, G.N. (검색결과 2 건)
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Investigating behind the lining of the Tunnel of Eupalinus in Samos (Greece) using ERT and GPR
Tsokas, Gregory N.,Jung‐,Ho, Kim,Tsourlos, Panagiotis I.,Angistalis, Georgios,Vargemezis, Georgios,Stampolidis, Alexandros,Diamanti, Nectaria Wiley (John WileySons) 2015 Near surface geophysics Vol.13 No.6
<P>The 2.5-km-long Eupalinian Aqueduct in the island of Samos, Greece, comprises the most impressive sample of ancient Greek engineering surviving almost intact. The main construction is a tunnel 1036 m long and almost 1.8 m wide excavated from both ends into mainly the massif limestone. In some parts of the overall length of about 240 m, the tunnel is dressed by lining of archaic and Roman age. This is of remarkable quality, and presumably, it protected the parts of the tunnel that were affected by subsidence and cave-ins. At some particular locations, it suffers deformations and other failures. Thus, prior to its restoration and protection measures design, an integrated geophysical survey was carried out on the faces of the supporting walls, consisting in ground-penetrating radar and electrical resistivity tomography works. The survey aimed to investigate the structure at the unseen area behind the lining. The thickness of the lining walls was accurately assessed by the ground-penetrating radar method and proved to be about 0.3 m-0.5 m on average. On the other hand, the width of the excavation behind the walls was predicted and checked at some particular locations with the electrical resistivity tomography works.</P>
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Papadopoulos, N.G.,Tsourlos, P.,Papazachos, C.,Tsokas, G.N.,Sarris, A.,Kim, J.H. Blackwell Publishing Ltd 2011 Geophysical prospecting Vol.59 No.3
<P><B>ABSTRACT</B></P><P>In this work a new algorithm for the fast and efficient 3D inversion of conventional 2D surface electrical resistivity tomography lines is presented. The proposed approach lies on the assumption that for every surface measurement there is a large number of 3D parameters with very small absolute Jacobian matrix values, which can be excluded in advance from the Jacobian matrix calculation, as they do not contribute significant information in the inversion procedure. A sensitivity analysis for both homogeneous and inhomogeneous earth models showed that each measurement has a specific region of influence, which can be limited to parameters in a critical rectangular prism volume. Application of the proposed algorithm accelerated almost three times the Jacobian (sensitivity) matrix calculation for the data sets tested in this work. Moreover, application of the least squares regression iterative inversion technique, resulted in a new 3D resistivity inversion algorithm more than 2.7 times faster and with computer memory requirements less than half compared to the original algorithm. The efficiency and accuracy of the algorithm was verified using synthetic models representing typical archaeological structures, as well as field data collected from two archaeological sites in Greece, employing different electrode configurations. The applicability of the presented approach is demonstrated for archaeological investigations and the basic idea of the proposed algorithm can be easily extended for the inversion of other geophysical data.</P>
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