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Activity Name:

GPR-Scan

Activity Numbre:

44

Activity type

Other

Involved Workpackage

Flood defences
Emergency response
Knowledge infrastructure

Objective

The GPR is a promising non destructive non intrusive tool to achieve multiple goals. In Polder2Cs the objective was to discover the opportunity of this tool by scanning specific areas in the dike with Ground-penetrating radar in order to explore the soil to different depths especially the upper layer, to make some analysis to detcect the structure of the dike and to compare later the results with other techniques applied in the same areas for detecting animal burrows, remote sensing, etc .

Activity Brief descriptor

Ground-penetrating radar is used to scan specific areas of the levee, then the results are compared with outputs of other surveying activities in the same areas (erosion experimentations, grout excavation, smoke injection, etc.)

Linked to theme(s):

Breaching
Animal- & vegetation-induced anomalies
Erosion processes
Temporary levee repairs
Levee survey & monitoring technique
Prolonged collaboration

Activity Time

Start Date:

Sept. 7, 2021, 10:01 a.m.

End Date:

Nov. 25, 2022, 2:33 p.m.

Active time length:

Days:

4

Hours:

None

Other:

4 GPR scans were realized in field on September 8th 2021, October 7th 2021 , 24 November 2021 and on the Baie de Somme in France on November 25th 2022.

Location

Levee stretch:

Other

Coordinates/ Latitude (WGS):

None

Coordinates/ Longitude (WGS):

None

Coordinates/ Altitude (mTAW):

None

Descriptor:

The sub-activities contain the exact location of each scan. 3 of them were realized in the Hedwige-Prosperpolder between belgium and Netherland and one in the Baie de Somme in France

Other references:

Data

Data: 1

Data type: pdf report
Description: The Ground Penetrating Radar for inspecting levee upper layer in Polder2Cs
Date availability: May 3, 2022
Find at: https://stowanl-my.sharepoint.com/:b:/g/personal/llhpp_stowa_nl/ET2rYdSsAAVIpeEuy1Yb8s4BHr-8paxA9zC5CorA_PUy0A?e=tkDJjz
Media avaliable:
Find media:

Relationships with other activities

Detaled information about the activity

Pre-conditions

To scan on the polder we should pay attention to the steepness of the dike , the texture of the scanned surface, the reference system of the scanned lines or grides. It is important to mesure the soil water contents. Regarding the used devices, K2Fastwave software should be already installed, configurated and prepared for for data acquisition Depending of scanning depth the suitable GPR frequency may be chosen.

Activity Descriptor

See "During Activity Field"

Equipments

Equipment: 1

GPR- 2G Hz (Ground-penetrating radar). (IDS) You find some photos in the link: https://drive.google.com/drive/folders/1mFjKytG5M_yOyXRia9dahQ1txw3mjD9o?usp=sharing
This GPR may give an accurate image for the upper layer of the soil (almost 50 Cm)

Equipment: 2

GPR- 200-600 M Hz (Ground-penetrating radar). (IDS) You find some photos in the link: https://drive.google.com/drive/folders/1cSYRQVq3BG5QiE-N0GzIGh-EQ6lTK7IZ?usp=sharing
This GPR may give an accurate image for a depth of many meters

Monitoring & Sensors

Beside the scanner we used a humidity sensor. The sensor is connected to a mobile application using bluetooth, We insert the sensor in the soil, wait the measured value to be stable, record it, repeat the measurement in many points (minimum 3) in the scanned area.
The Humidity is a parameter that affect the propagation of the GPR waves. So we use a humidity sensor for monitoring.

Sensor: 1

Humidity sensor. We use one of the following types: FDR: Frequency Domain Reflectometry TDR: Time Domain Reflectometry https://drive.google.com/drive/folders/1mFjKytG5M_yOyXRia9dahQ1txw3mjD9o?usp=sharing

Limits

1) Soil Humidity: High soil humidity affects the propagation velocity of the electromagnetic waves. 2) Grass thickness and type: The thickness of the grass layer can reduce the precision of the distance measuring device that is included in the RIS ONE 2GHz radar. In addition, grass make the GPR device difficult to handle by hand. 3) Site topography: The site topography, especially steep slope, makes the movement of the GPR cart more difficult, even with the Opera Duo cart that is equipped with adapted wheels. The operator have to be careful during the scan. 4) The autonomy of the batteries of the GPR

During Activity

1- At first we identify the area 2- Regarding the wanted accuracy and the surface of the area, we can specify the spacing between the logitudinal lines (and transversal lines if necessary), then mark the lines of the grid on the soil. 3- Scan the area : - longitudinally and transversely when you use RIS ONE 2GHz. In order to adapt the RIS ONE to our experimentations, we used a wooden plate with predefined scan paths that facilitates the movement of the GPR. We can see the images of those plates in the linked data. - Parallele lines with a fixed step between the lines when you use the Opera Duo 200 MHz and 600 MHz 4- Verify that the recorded length of each scaned line in the software corresponds to the real scanned distance. 5- Save the data

Post-activity conditions

The row data obtained from the GPR scan needs to be deeply analysed to get useful information. Usually the GPR row data is analysed following 3 step process : - A SCAN : the images represent a number matrix ( on interpolating 2 dimension levels.) - B SCAN : the images are obtained from A Scan interpolation by applying filters - C SCAN : The third analysis consists on a 3D interpolation To process the data, GPR data processing softwares (GRED HD and Reflex) have to be installed and configured. The 2GHz GPR is not commonly used to scan the upper layer of the soil. The team of the university of Lille is developing a processing method to get interesting and useful results basing on this scan. This analysis procedure is partially applied on the polder2Cs row data.

Immediate Results

We can get the row data and the A-scan immediately on the field (see post activity conditions)

Results /Conclusion

B and C scan (see post activity conditions)

Infrastructure Knowledge

Other key information