Building Distress Evaluation Using Seismic Refraction and Multichannel Analysis of Surface Waves: A Case Study of Millennium Estate Araromi, Gbagada, Lagos, South- Western, Nigeria

Abstract

Integration of Seismic refraction and Multichannel Analysis of Surface
Waves (MASW) was used to assess the subsurface information in order to
establish the causes of sinking and tilting of buildings at Millennium Estate
Gbagada, Lagos. Four traverses of equal length of 69 m were picked oriented
in the north to south. Seismic data were collected using the ABEM Terraloc
Mk.6 with a 24channel recording system. Forward and reverse shooting as
well as Multichannel Analysis of Surface Waves (MASW) using split spread
shooting methods were carried out within the study area. Each collected shot
record of the surface wave was quality controlled and processed using the
Seisimager software. The results indicate the presence of three subsurface
layers with the first layer having velocity 300 m/s and thickness 1.0 – 6.0m,
representing topsoil (clayey materials). The second refractive layer is
composed of dry loose sandy soil with thickness 6.0 – 13.0 m and velocity 580
– 700 m/s. The third refractive layer consists of saturated clay materials (clay
and shale) with a velocity of 1000 m/s. The delineated refractive layers are
characterized by an increase in velocity with depth. The results of both
approaches reveal that the topsoil (Clay), loose sand, and saturated clay/shale
unit are incompetent materials, thus leading to the sinking and tilting of
buildings within the study area. This study has been able to use integrated
methods of geophysical investigation to provide an understanding of the
subsurface condition for evaluating building distress.