Laboratory Studies Using Electrical Resistivity Tomography and Fiber Optic Techniques to Detect Seepage Zones in River Embankments

Azadeh Hojat,Monica Papini,Laura Longoni,Greta Tresoldi,Luigi Zanzi,Vladislav Ivov Ivanov,Diego Arosio,Andrea Madaschi,Maddalena Ferrario,Marco Brunero

doi:10.3390/geosciences11020069

Abstract

We present the results of laboratory experiments on a down-scaled river levee constructed with clayey material collected from a river embankment where a permanent resistivity instrument has operated since 2015. To create potential seepages through the levee, two zones (5 × 4 cm and 10 × 2 cm) were filled with sand during the levee construction. Electrical resistivity tomography (ERT) technique and Fiber Bragg Grating (FBG) technology were used to study time-lapse variations due to seepage. The ERT profile was spread on the levee crest and the Wenner array with unit electrode spacing a = 3 cm was used. Six organic modified ceramics (ORMOCER) coated 250 μm-diameter fibers were deployed in different parts of the levee. Time-lapse measurements were performed for both techniques from the beginning of each experiment when water was added to the river side until the water was continuously exiting from the seepage zones. The results showed that ERT images could detect seepages from the early stages. Although with a short delay compared to ERT, fiber optic sensors also showed their ability to detect water infiltrations by measuring temperature changes. Both technologies being successful, a discussion about respective peculiarities and pros and cons is proposed to suggest some criteria in choosing the proper technique according to the specific needs.

Highlights

In the recent decade, hydrogeological risks have increasingly demanded development of proper solutions to be implemented in early warning alarming strategies
We presented the results of laboratory tests using Electrical resistivity tomography (ERT) and fiber optic techniques to monitor seepage zones through a down-scaled river levee
This is due to different measurement principles, which in the ERT method is based on the injection of current from near-surface electrodes into large volumes of the levee body to produce a tomographic map of its resistivity, while the latter method requires the water seepage to approach the close vicinity of the fiber sensors

Summary

Introduction

Hydrogeological risks have increasingly demanded development of proper solutions to be implemented in early warning alarming strategies. One of the most important and widely spread hydrogeological risks is the failure of earthen embankments that can happen on the slopes of roadways and railways, earthen dams, and river levees. Having the capability of determining anomalous water saturation areas, as well as detecting seepage zones, the ERT method has been increasingly used to monitor the internal conditions of earthen embankments [21,22,23,24,25,26,27,28]. The first pilot site was the levee of an irrigation canal in San Giacomo delle Segnate, northern Italy, where the unit electrode spacing a = 1 m was used [24]. The second pilot site was a critical section of the levee of Parma river in Colorno where the unit electrode spacing a = 2 m was used [21]

Results

Discussion

Conclusion