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The contribution of geophysics to archaeology: a case study of an ancient canal of the Oc Eo culture in the Mekong Delta, Vietnam

Le Ngoc Thanh, Nguyen Quang Dung, Nguyen Quang Bac, Nguyen Quang Mien, Nguyen Dan Vu, Duong Ba Man, Nguyen Dinh Chau

Geology, Geophysics and Environment

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2019

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Vol. 45, no. 1

45--56

EN

Generally, underground ancient canals are infilled with alluvial materials, with the canal bed and substrate often having different resistivity values. This study aimed to determine the location and morphology of Malleret’s ancient canal 16 located to the southeast of the Ba The mountain, Mekong Delta, Vietnam by means of geophysical techniques. Two geophysical methods were used: electromagnetic profile and electric resisitivity tomography. A geoelectric structure 70 m long with 70–95 mS/m of apparent conductivity was found. On the electrical resistivity tomography section, a resistivity zone of 10–20 Ω∙m, 1–4 m deep, 70 m wide corresponds to the mentioned above geoelectric structure, which is in an asymmetric U-shape extending toward the southeastern bank of canal 16. Hand-augering confirmed that the canal bed is fully incised into Holocene sediments as a substrate which stretches down to the Pleistocene. The sediments are composed of loams mixed with plant remains with a resistivity ρ ~ 10–15 Ω∙m. Both of the canal banks at a depth of 5 m are made up of Holocene sedi-ments (ρ ~ 4–10 Ω∙m). The 14C measurements determined the age of the organic matter in the canal as being equal to 1210 ±85 BP, suggesting canal 16 ceased being operational at that time. The precise positioning of canal 16 on the ground surface, as well as identifying the morphology of the canal bed, were corroborated by geophysical techniques. The obtained results are of considerable value to archaeologists.

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The application of electromagnetic methods for polymetallic prospecting in mining conditions

Gołębiowski T., Żogała B., Mendecki M., Małysa T.

Geology, Geophysics and Environment

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2017

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Vol. 43, no. 3

181--189

EN

The paper presents selected results of geophysical surveys carried out in the “Polkowice-Sieroszowice” copper mine in Lower Silesia, Poland. The aim of complex geophysical measurements was the analysis of the usefulness of selected electromagnetic methods for locating ore mineralisation zones in mining conditions. The results were obtained from surveys conducted along profiles designed on the side-wall by the roof, in the middle and the floor of the excavation. Electromagnetic Profiling and Ground Penetrating Radar techniques were applied for outlining the mineralisation zones consisting of Cu, Pb and Fe. The variability of geophysical recordings depending on the degree of mineralisation and distribution of fractures induced by mining activity were analysed. The results of geophysical surveys were correlated to petrophysical parameters and laboratory data concerning the percentages of Cu, Pb and Fe in samples taken from the side-wall at the survey site.

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Metody wyznaczania rezystywności gruntu

Rudzki M.

Ochrona przed Korozją

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2006

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nr 8

256-258

PL

Zagadnienie poprawnego określania rezystywności gruntu odgrywa istotną rolę przy ocenie agresywności korozyjnej gruntu oraz w projektowaniu systemów ochrony katodowej. Najczęściej w tym celu używana jest metoda elektrooporowa (w wariancie sondowań lub profilowań). Metoda ta jednakże może okazać się żmudna i czasochłonna, co często skutkuje wyrywkowymi pomiarami na badanym odcinku/obszarze. Alternatywą dla metody elektrooporowej jest metoda dipolowego profilowania indukcyjnego. Zalety tej metody to: szybkie wykonywanie pomiarów w terenie (zwłaszcza przy wykorzystaniu systemu GPS), ciągłość pokrycia pomiarami, dokładne określenie rezystywności gruntu, duża odporność na zakłócenia spowodowane przypowierzchniowymi niejednorodnościami gruntu. W rejonach, gdzie pożądana jest dokładna znajomość zmian rezystywności gruntu wraz z głębokością, stosowana może być metoda penetracyjnego profilowania rezystywności. W metodzie tej wykorzystywany jest próbnik elektryczny, wprowadzany do gruntu za pomocą wibromłota, zwykle zamontowanego na samochodzie. Metoda ta dostarcza informacji o rezystywności gruntu z największą możliwą dokładnością i rozdzielczością pionową, niemożliwymi do osiągnięcia za pomocą metod powierzchniowych. Łączne użycie obu tych metod przyczynić się może do znacznego wzrostu ilości pomiarów i jakości wyników określenia rezystywności gruntów.

EN

The issue of determining the proper ground resistance plays an important role in designing cathodic protection systems and in assessing the intensity of ground corrosivity. A DC current method (in the form of sounding or profiling) has been most frequently adopted for this task; however, it can be laborious and time-consuming, which results in poor spatial sampling of the surveyed distance/ area. An attractive alternative for the DC current method is the dipole electromagnetic profiling method. The advantages of this method include prompt field data acquisition (especially when aided by a GPS system), continuous spatial coverage, precise and accurate determination of the ground resistance and strong immunity to near-surface inhomogenities. In areas where a detailed depth ground resistance distribution analysis is required, direct push resistance profiling can be applied. The method uses an electrical probe, which is driven into the ground with a high power percussion hammer normally mounted on a vehicle. This method can yield information about the ground resistance with unsurpassed accuracy and vertical resolution, thus resolving any ambiguities that may arise from surface surveys. The combined usage of those two methods can contribute to a significant increase in both the productivity and accuracy of determining ground resistance.