GPR Data Acquisition and Interpretation

Transcription

1 1 GPR Data Acquisition and Interpretation Mezgeen Rasol PhD Candidate Geophysics and Seismic Engineering Polytechnic University of Catalonia BIG-SKY-EARTH Cost Action TD143 Workshop Novi Sad, Serbia February 26 th -27 th, 218 Copyrights 218 by Mezgeen Rasol

2 2 Outlines 2 nd case study 1 st case study GPR Applications GPR Concept GPR Introduction

3 3 1. GPR Introduction Ground Penetrating Radar (GPR) is a non-destructive geophysical survey method. Nowadays, the use of GPR has been enormously wide in civil engineering applications. GPR instrumentation is commonly consists of three main modules: 1. Control Unit 2. Antenna Unit Transmitter Receiver 3. Power supply and Survey Wheels

4 4 2. GPR Concept GPR sends electromagnetic energy into the ground through a Transmitter Antenna, and the transmitted energy gets reflected wherever there is a Dielectric Contrast between the subsurface layers. The reflected energy is collected by Receiver antenna and is displayed in real time on the screen of the Data-Logger. Monostatic and Bistatic antennae : If the Transmitter and Receiver are housed in a single transducer, it is Monostatic. Otherwise, it is Bistatic. Silty sand Limestone Limestone Pipe Sand stone Marine ss Clay Shale

5 5 3. GPR Applications Field Applications Architecture and Architecture Cultural Heritage Civil Engineering Foundation soil identification. Checking for cracks and fissures in walls and roofs. Localization of oxidation and water content in Reinforced Concrete (RC). Soil identification under rigid frames. Identification of cavities in calcareous soils. Localization of concrete buried structures. Checking the bridge decks and rebar s Checking the road pavement projects. Checking the airports projects. Checking the railways projects. Seismic zonation and assessment. Tube detection in roads. Mining Industry Localization of mineral deposits. Determination of water levels in gas or oil reservoirs. Localization of conduits, manholes and gas chambers. Hydrology Localization of phreatic level. Identification of aquifers. Copyrights 218 by Mezgeen Rasol Cultural Heritage Archaeology Agronomy Forensic Medicine Glaciology Armed Forces Marine scientific research Determination of structural damage. Quality control of maintenance and repairs. Localization of electrical cabling or Assessment of Cultural Heritage. water pipeline. Detecting of hidden structures Determine and detecting damages. Localization of architectural and ancient civilizations remains. Identification of fossils and mass graves. Mapping buried structures. Control of soil maps. Localization of bedrock. Localization of phreatic level. Identification of contaminated areas. Determination of surface moisture content. Localization of buried bodies. Localization of hideouts and illegal tunnels. Localization of the Cemeteries Determination of ice sheets in glaciers. Geomorphological study of glaciers. Identification of landmines and hideouts. Determination of marine geomorphology. Identification of sedimentary structures.

6 6 Typical table stated the recommended GPR frequency and appropriate applications. Choosing antenna depend on the depth of penetrating and the type of the medium. Center Frequency (MHz) Depth of Penetration(m) Typical Applications 16.5 Concrete Evaluation Concrete Evaluation, Void Detection Utility, Engineering, Environmental, Void Detection Utility, Engineering, Geotechnical Geotechnical, Engineering, Environmental Geotechnical, Environmental, Mining Geotechnical

7 7 4. Cervantes Park Underground Streams GPR Survey Step 1. Positioning of the noisy location depending on the previous studied. Step 2. GPR Data acquisition using 1 MHz GPR Shielded GSSI antenna, consisted of five Profiles. Step 3. GPR Data Processing by ReflexW. and interpretation. Step 4. Geo-referencing anomalies. Step 5. Comparing to H/V Method.

8 Distance ( m) 8 Sample Profile Filtered Data 1 st Set of Filters by ReflexW TWT (ns)1 2 5 Dep th (m ) ( v=.1 m/ns) Possible Interpretation TWT (ns)1 2 A6 Anomalies A7 5 1 D epth (m) ( v=. 1 m/ns) 3 15 Distance ( m) Filtered Data 2 nd Set of Filters by ReflexW TWT (ns)1 5 Depth (m) ( v=. 1 m/ns)

9 9 Anomalies Map 14 noisy areas (Anomalies) are interpreted on radargrams and these anomalies could corresponding to underground streams.

10 1 5. Analysis and Calibration of The GPR Antenna GPR/MALA RAMAC shielded antennas: 5 MHz, 8 MHz and 1.6 GHz. 5.1 Stability Test Used two media for comparing ; Case 1. Using GPR in the air because of its simplicity for interpretations. Case 2. Using GPR on the ground surface, to compare with air results. 5 MHz 8 MHz 1.6 GHz

11 11 For 5 MHz, Three Measurements taken For 8 MHz, Four Measurements taken For 1.6 GHz, Three Measurements taken

12 12 Stability and changes in amplitude of the various shielded antennas. GPR Antenna GPR Measurements 1 st Case 2 nd Case AIR Δ A GROUND 5 MHz Δ A AVERAGE MHz AVERAGE GHz Conclusions: Δ Amplitudes on the ground and in the Air AVERAGE Time Zero Test Antennas Distance (cm) TwT (ns) Reflection Wave Time (ns) Zero Position Time (ns) 5 MHz MHz GHz Zero Position Reflection wave Zero Position Zero Position Reflection wave Reflection wave All the antennas working properly and stable but 5 MHz is more stable.

13 5.3 Stacking Test MHz 1.6 GHz Conclusions: Stack values: 1, 2, 4, 8, 16, 64, 128, 256 and MHz In high-resolution frequency antenna GPR effect of increasing the stacking values are more clearly. Suitable stacking value depend on the type of applications. Stacking value 1 is considerable noisy level, its an appropriate stack value.

14 14 References [1] Joachim Ender. 98 Years of the RADAR Principle: The Inventor Christian Hülsmeyer. EUSAR 22 [2] Kozlovsky, E.A. (ed), Encyclopaedia of Mining (in Russian). Ed. Sovietic Encyclopaedia. 4, [3] Finkelshtein, M.I., Kutev, V.A., Zolotared, V.P., Applications of ground penetrating radar in geological engineering (in Russian). Ed. Nedra. Moscow. [4] [5] (access: 214/5/26). [6] HULSENBECK et al.: German Pat. No , 1926 [7] STEENSON, B..: 'Radar methods for the exploration of glaciers'. PhD Thesis, Calif. Inst. Tech., Pasadena, CA, USA, 1951

15 Many Thanks for your attention 15