Soil piping: networks characterization using ground-penetrating radar

Abstract

Soil plpmg remains a relatively unexplored phenomenon despite its substantial impacts on watershed scale water and sediments transfer in numerous locations around the world. One of the main limits regarding the study of this singular process is characterization of the pipe networks (defining number, position, dimension and connectivity of pipes). In this context, non-invasive sub surface imaging using ground-penetrating radar (GPR) seems a promising technique. An exploratory methodology was developed to assess the ability of GPR to characterize pipe networks in Loess-derived soil. This methodology relies on (1) high spatial resolution scanning and (2) detection of electromagnetic sub-surface indicators of soil pipe (reflection hyperbolas and strongest reflections). For a 50 m x 50 m scanned zone, results show that combining these indicators can provide interesting clues about a potential pipe network.Three probably interconnected pipes were revealed. However, results show that the proposed methodology needs specific improvements in signal processing, object detection and system configuration in order to enhance and facilitate sub surface networks characterization.

Detection of Soil Pipes Using Ground Penetrating Radar

“…This study in a complex way has confirmed that GPR can be used to detect soil pipes: this is in accordance with previous reports [7,[18][19][20][21]. The reflections on radargrams that indicate soil pipes are well visible because there are significant differences in radar-wave response given by pipes filled with air and with water at the bottom (Figures 4e, 7d and 10c), and with the surrounding soil.…”

“…The soil pipes were filled with air, and in the bottom the increased soil moisture and water were present. These subsurface tunnels are reflected on radargrams as reflection hyperbolas when they are crossed transversely, as singular strong reflections [18], or as an anomaly in the reflections [8]. All reflections that might potentially suggest pipe occurrence were interpreted in their relation to others within a profile, or between two consecutive profiles and they were related to the surface indicators of piping (i.e., sagging of the ground or pipe roof collapses).…”

“…Among these methods, GPR has received the most attention, even though it seems that the potential of this method has not yet been fully exploited. Most reports have presented the preliminary results of GPR application in the detection of soil pipes [7,8,20], including only short conference abstracts [18,19]. On one occasion GPR was used to establish hydrological connectivity between pipes through the use of a tracer solution [21] and to estimate the pipe length [8].…”

“…On one occasion GPR was used to establish hydrological connectivity between pipes through the use of a tracer solution [21] and to estimate the pipe length [8]. Antennas of different frequencies were used, e.g., in the northern Pennine Hills (UK)-100 and 200 MHz [7,21], in the Bieszczady Mountains (Poland)-500 MHz, and in the loess belt in Belgium (Sippenaeken and Kluisbergen)-200 and 400 MHz [18,19].…”

“…Moreover, this study has emphasized the critical key in GPR surveys of soil piping, i.e., the selection of antennas with appropriate frequency which allowing the identification of pipes of different sizes and depths of Geophysical methods seem to be a promising tool to provide new, more detailed information on subsurface pipes. In natural environments, the following methods have already been tested in soil piping research: electrical resistivity tomography (ERT) [8,[13][14][15], seismic refraction tomography (SRT) [16], self-potential (SP) [17], and ground penetrating radar (GPR) [7,8,[18][19][20][21][22]. Under laboratory conditions, active and passive acoustic techniques have been tested to study pipe flow and internal erosion [23].…”