Investigation into the types of fracture and viable depth to substratum of a housing estate using geophysical techniques

Abstract

Mapping of the configuration of bedrock is paramount in civil engineering and hydrogeological settings. In civil engineering, areas that are extensively fractured (either shallow or deep) are adjudged as weak zones whereby these provinces are regarded as copious zones for groundwater exploration. Very Low Frequency Electromagnetic (VLF-EM) and ground magnetic survey were carried out in Olupona Housing Estate along seven traverses with interstation spacing of 20 m. For the two methods, traverses 1 to 3 were taken in North-South azimuth which covered distance 300 m while traverses 4 to 7 were acquired along East-West azimuth which covered distance 400 m. VLF-EM results revealed Type-1 fracture along traverse 1, traverses 2 to 4 showed no fracture but a fairly competent bedrock. Type-2 fractures were revealed on traverses 5 to 7 while Type-3 fracture was shown on traverse 5 alone. Ground magnetic results depicted that the depths to biotite or biotite muscovite granite are relatively deep. The mineral rocks with very thin, intermediate, and very thick bodies have their depths range as 14.7 m, 11.0 m and 8.8 m respectively. On the average, the depths to these mineral rocks from the surface varied from 6.5 to 19.6 m. The trends of the identified fractured zones are NE-SW and NW-SE directions. It is concluded that in order to avoid building collapse in future, construction of high-rise buildings is unadvisable in the study area. If the identified fractured zones are properly maximized for groundwater exploration, the fractured zones can be optimized such that reservoir(s) can be constructed so as to supply water to the houses for domestic usage.