GPR for river dyke - GSB

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In Appendix A, we have derived how the wave speed and propagation attenuation are related to the ground material properties. According to equation A4 in Apendix A, the wave velocity can be written v 2 f k real 1 0 r c r where c is the speed of light in air and c = 0.3 m/ns. The list of wave speeds in ground materials shown in Table 1 is calculated by using the above equation. A general rule is that for detecting deep targets one uses low frequency and long antennas. Assuming the detection distance is 5 wavelengths and knowing the antenna length is half wavelength, we obtain that the detection distance is 10 times of the antenna length. The above empirical relationship can help to choose antenna lengths according to the detection depth. The resolution is also related to the wavelength used. Here we adapt the criterion that the detection resolution is ¼ wavelength, i.e., half of the antenna length. Hence our 10 cm antenna is best suited for detection distance 1 m with a resolution 5 cm, while our 1.2 m antenna is best suited for detection distance 12 m with a resolution 60 cm. 6 Conclusions The tests during this on-site training period show that GPR can make quick and continuous measurements on river dyke etc. GPR can provide high-resolution image of the ground layering information. Two types of antennas are used for measurements, one is 10 cm antenna, and the other is 1.2 m length antenna. It is known that on top of the dyke there is 6 cm thick asphalt carpeting with stone chips. Below the asphalt layer there is 13 cm thick compacted layer of brick chips mixed with sand (Locals inform maximum thickness of the brick chips layer is about 40 cm). Below brick chips there is sand. There is no brick soling below the brick chips layer. GPR test using 1.2 m antenna cannot resolve the layers with thickness 6cm and 13cm. However, Figures 3 and 5 show that using 10 cm antennas can detect those layers. GPR can be used to detect the material discontinuities along the measurement direction (e.g., see Figure 13 and 15). Those discontinuity locations may suggest that the ground is built by different materials or the ground is deformed, and may indicate weak locations of a dyke.
Kontroll- og referanseside/ Review and reference page Dokumentinformasjon/Document information Dokumenttittel/Document title On site training of using GPR (ground penetrating radar) for river dyke monitoring in Bangladesh Dokumenttype/Type of document Rapport/Report Teknisk notat/Technical Note Oppdragsgiver/Client Geological Survey of Bangladesh Distribusjon/Distribution Fri/Unlimited Begrenset/Limited Ingen/None Emneord/Keywords Geophysics, Ground Penetrating Radar, river dykes Stedfesting/Geographical information Land, fylke/Country, County Bangladesh Kommune/Municipality Dhaka Sted/Location Dhaka Kartblad/Map UTM-koordinater/UTM-coordinates Dokument nr/Document No. 20092021-00-6-R Dato/Date 22 Nov. 2011 Rev.nr./Rev.No. 0 Havområde/Offshore area Feltnavn/Field name Sted/Location Felt, blokknr./Field, Block No. Dokumentkontroll/Document control Kvalitetssikring i henhold til/Quality assurance according to NS-EN ISO9001 Rev. / Rev. Revisjonsgrunnlag/Reason for revision Egenkontroll / Self review av/by: Sideman ns- kontroll/ Colleagu e review av/by: 0 Original document FK RKB LT Uavheng ig kontroll/ Independ ent review av/by: Tverrfag lig kontroll/ Interdisciplin ary review av/by: Skj.nr. 043
Page 1 and 2: GOVERNMENT OF THE PEOPLE’S REPUBL
Page 3 and 4: Summary The Norwegian Geotechnical
Page 5 and 6: 1 Introduction The Geological Surve
Page 7 and 8: Figure 2: GSB personnel operating t
Page 9 and 10: Figure 5: Radargram for the test on
Page 11 and 12: new pitch road has been made. The t
Page 13 and 14: 4.2.3 GPR survey on Prottasha bridg
Page 15 and 16: Figure 15 shows the radargram for G
Page 17: In Figure 20, there is no continuou
Page 21: Kontroll- og referanseside/ Review

GPR for river dyke - GSB

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