Application of Geophysical Methods in Foundation Failure Investigation in the Metro Hostel, Camp Area, Abeokuta, South Western Nigeria

Abstract

This study was carried out to assess the causes(s) of the foundation failure of the Metro Hostel Building opposite Mechanic Village, Camp Area, Abeokuta, Nigeria, using combined geophysical techniques which comprises of Vertical electrical sounding (VES) and Seismic Refraction methods. The major affected structure is a two storey building leaning and having severe foundation based cracks. The PASI – Earth (16 GLN) resistivity meter was used for resistivity data collection and ABEM Terraloc MK -6 Seismograph for velocity data collection. The result of the vertical electrical sounding gives a maximum of three sequences: topsoil, weathered layer (clayey sand/sandy clay) and fractured rock/fresh basement with a maximum value of 10.38 m depth to the basement. The result was complemented and corroborated by seismic refraction method which also gives three main velocity layers with the second layer velocity ranges from 680 and 950 m/s with thickness value ranging from 6.80 – 8.27 m and a total depth -to-bedrock of 10.27 m.  The presence of clayey materials identified in the study area posed a threat to three buildings erected. It is concluded from the study that the building structure failed due to incompetent clay layer and improper foundation design on some part of the building which is pronounced by the observed tilting and cracks. It is suggested that reinforcement, concrete packing and buttress pillars should be done around the buildings especially in areas with more pronounced subsidence to avoid total collapse.