Building Collapse Study Using Near Surface Geophysical Method in Parts of Akwa Ibom State, Nigeria

Abstract

Adequate knowledge of the geology and the structures of the subsurface would assist engineers in the best way to carry out constructions to avoid building collapse. In this study, near surface seismic refraction method was used to determine the geotechnical parameters of the subsurface. The refracted travel times of all recorded traces were picked and analyzed using seisImager packages of pickwin and IXrefract software. The seismic tomography section revealed two geologic layers in the study area. That is, layers 1 and 2.  The P-wave velocity of the first layer ranged from 500.4 to 901.2 m/s while in the second layer, the velocity was between 720 and 1010.3 m/s. The S-wave velocity of the first layer ranged from 400.0 and 720.5 m/s, 510.0 and 901.2 m/s in the second layer respectively. In layer 1:  Poisson ratio ranged from 1.49 to 1.99, Young’s modulus ranged from between -425.1 to -2021.1 KN/m², Lames constant ranged from 245.8 to 313.8 KN/m², Shear modulus ranged from -613.1  to -2518.7KN/m², Ultimate capacity ranged from 680.0 to 1282.7 N/m², Allowable capacity ranged from 170.0  to 320.7 N/m², Material index ranged from 0.97 to 2.97, Concentration index -1.03 to 132.8, Density gradient ranged from -3.98 to -4.99 and Stress ratio ranged from 0.007 to -0.16. In layer 2: Poisson ratio ranged from 1.36 to 2.94, Young’s modulus ranged from between 240.5 to 1597.7 KN/m², Lames constant ranged from -108.5 to 965.8 KN/m², Shear modulus ranged from 432.9 to 3153.1 KN/m², Ultimate capacity ranged from 102 to 180.24 N/m², Allowable capacity ranged from 255.0  to 450.6 N/m², Material index ranged from 0.43 to 6.97, Concentration index 0.09 to 7.99, Density gradient ranged from -3.71 to -6.89 and Stress ratio ranged from -1.51 to -3.80. The geologic formation in the second layer was found to be more competent than the first layer with high allowable capacity and low ultimate failure potential.

Keywords- Building collapse, Near surface, Geophysical, Young Modulus, Shear Modulus

DOI: 10.7176/JNSR/10-4-03

Publication date: February 29^th 2020