Forensic geotechnical investigation of cracks in buildings around Gubi and environs, Bauchi, Northeast Nigeria

Abstract

The study aims to undertake a geoforensic investigation of the major causes of cracks in 
buildings in Gubi and its environs. To achieve this, geophysical and geotechnical approaches 
were adopted to characterize the soil properties and subsurface rocks. Five vertical elec
trical soundings (VES) were purposively carried out using Schlumberger’s configuration 
to characterize the geoelectrical properties of the soil. In addition, 10 disturbed soil sam
ples were collected for geotechnical laboratory analyses. The indices analyzed are natural 
moisture content (NMC), particle size distribution, Atterberg limits, free swell index, linear 
shrinkage, and specific gravity. Three geoelectrical layers comprising topsoil, weathered 
layer, and bedrock basement were delineated within the study area. The resistivity values 
(10.8–42.8 Ωm) suggest that the top and weathered layers of VES 1 and VES 2 are incom
petent clay material. The results of the geotechnical tests, however, revealed that the 
site is underlain by poorly graded clay sand to sand clays with low to medium plasticity, 
specific gravity (2.2–2.7), liquid limit (25.8%–39.0%), plastic limit (18.8%–35.1%), NMC 
(7.10%–25.0%), and linear shrinkage limit (2.8%–11.3%). The result generally shows that 
the soils in the northeastern parts have NMC, linear shrinkage, and free swell value above 
the permissible limit for a foundation. It was concluded that the differential settlement of 
the incompetent subsoil material is responsible for the failure of the foundation material 
and building walls.