Desiccation cracking detection using 2-D and 3-D electrical resistivity tomography: validation on a flood embankment

Desiccation cracks forming in earthen structures are a known source of engineering concern. In particular such fissures forming in flood embankments can affect their stability leading to failure when overtopped. These and other problems related to safety have raised the importance of using efficient and reliable tools, especially when relatively fast, non-invasive and extensive investigations are required. Geophysical techniques, such as Electrical Resistivity Tomography (ERT), allow for accurate assessment and monitoring of shallow depths within engineering structures.
The presented study examines the use of miniature and field scale ERT on a fissured flood embankment near Hull, UK. Two separate sections were surveyed in summer and winter using both 2-D and 3-D configurations, allowing seasonal evaluation of embankment condition.
The field results were validated through forward modelling, with different fissure configurations and the effect of topography. The results show that the resolution of the cracks increased with smaller electrode spacing. It was found that ERT can be used on a larger scale to detect zones of fissuring with fissured networks being displayed. The ability to detect cracks was diminished when surveying in winter with cracks reducing in size due to seasonal swelling of the soil. The resistivity models obtained showed anomalies with far lower resistivity than those obtained in summer.
The study showed that miniature surveys could be used to examine small sections in detail allowing imaging for horizontal subsurface fissures. The larger scale surveys provided important spatial information allowing the distribution of fissures on the embankment to be made.
The study recommends that geophysical surveying of flood defences should be used as a routine assessment tool to detect desiccation cracks within the embankment, and that these surveys should be completed in the summer, where cracks are most prominent.