Recruiting the Very Low Frequency Electromagnetic Geophysical Technique for the Characterisation of Two Eroded Soil Pipes in Awka, Anambra State, Nigeria

Abstract

Many soil subsidences are due to tunnel erosion, popularly called "soil pipe, which generally begins as a tiny flute hole in the ground but may cause significant environmental implications when left uncontrolled. Varieties of damages resulting from soil subsidence have been reported in several regions within Anambra State, Nigeria. Therefore, the study focuses on examining areas in some parts of the state where soil pipes, a subsurface form of erosion, are prevalent. The research aimed to investigate soil pipes located inside soil subsidence at two Awka sites: Awka site I, and Awka site II, which are geographically positioned at "6.22320oNand 7.08240oE" and "6.22200oN and 7.08190oE," respectively. The Very Low Frequency Electromagnetic (VLF-EM) geophysical technique was used to survey the areas, generating four profiles. Two profiles in each of the study areas, each with a traverse length of 100m and spacing of 5m. Results indicated that the study areas have developed a void-like vertical structure of approximately 5m in depth from the profile's top and has extended to about 4m in length. The Karous-Hjelt filtering has also indicated low conductivity (-10 to 0.5 Mhos), corroborating the maximum negative response of the Fraser filtering inside the soil subsidence structure of each site, while profiles distant from the piping structures did not indicate any cavity or low conductivity.