Non‐destructive assessment of retaining wall of former coal mine plant

Abstract

A large retaining wall (appr. 9 m high and 286 m long) of a former coal mine has been investigated using Ground Penetrating Radar (GPR), with two low frequency antennas (200 and 400 MHz), and Large Aperture UltraSound (LAUS) to gather information about the condition and inner structure of the wall. Three vertical lines were selected in representative areas of the wall to evaluate the usefulness of Non-Destructive Testing (NDT) with these two methods. The LAUS results showed the layer structure at one line where the wall was enforced by a concrete shell and were unspecific regarding the inner structure beyond the first layer. GPR results were able to be collected much faster and showed some internal features. Penetration was limited to 2-3 m due to the high absorption in the material.

A Review of GPR Application on Transport Infrastructures: Troubleshooting and Best Practices

“…This is the case in the analysis of changes in the soil salt content [121] or sulphate and chloride content [309]. Changes in the aggregate size also produces changes in the GPR images, showing a large scattering [310]. This effect has been detected in the ground studies [311,312].…”

“…Santos-Asunçao et al [121] use an 800 MHz center frequency antenna to detect a buried structure, and the 1 GHz and 2.3 GHz center frequency antennas in the assessment of the state of the buried walls, obtaining 3D images and GPR slices. Wiggenhauser et al [310] check the inner structure of walls using two antennas with lower central frequencies of 200 MHz and 400 MHz. In addition, several tests in laboratory [313] or in field surveys [115] recommend the use of a high-frequency microwave synthetic aperture radar between 1 GHz and 6 GHz in order to obtain B-scans or to generate 2D slice images.…”

“…Wiggenhauser et al [310] highlight the difficulty of the GPR and other NDT in the inspection of masonry retaining walls as a consequence of the limited access to the surfaces and their different stages of deterioration, whereas Santos-Assunçao et al [121] remark the problem in accurate data acquisition due to irregular stone surfaces and also the importance of the precise position of the antenna, proposing a laser guide marking for the profile lines.…”

Multimodal Nondestructive Evaluation of Industrial Heritage Structures

“…The result is a thermography like image which is composed of the phase determined for each pixel in the time lapse period. Technical reasons permitted measurements to be carried out at the Itzenplitz location; however, the principle was proven at a retaining wall which has been investigated previously [18]. An old, partially collapsed retaining wall of 8 m height and unknown backfilling was investigated to identify NDE methods capable of providing solutions necessary to assess its structural integrity.…”