Geoenvironmental Disasters (Feb 2020)
Characterization of structural failures founded on soils in Panyam and some parts of Mangu, Central Nigeria
Abstract
Abstract Structural failure of buildings, roads, and other infrastructures has led to the loss of lives and monumental damage to the economy. In developing countries such as Nigeria, the failures are always attributed to the nature/type of soils in the area without considering other factors. With the increase in civil engineering constructions and the scramble for a limited portion of competent soils for such constructions, land, therefore, is becoming man’s most priced commodity for agriculture, residential and industrial purposes. No works of such have been done in the area, it is, therefore, imperative to study the cause(s) to prevent further loss of lives and the negative effects of such on the economy. The study was carried out at Panyam and some surrounding localities on latitudes N9021′ and N9026′ and longitudes 9011′E and 9016′E an area of 72 km2. A total of forty samples were collected out of which twenty were selected for swelling potentials determination due to their cohesive nature within the 1.5 m depth. To characterize the swelling of the soils, inferential testing methods; direct method comprising Liquid Limit and Plasticity Index with values ranging from 30% – 70% and 10% – 27% respectively, and the indirect method (Free Swell Index, FSI) whose values range from 9.1% – 90% were used. Most of the soils analyzed based on the geotechnical standards were categorized relatively safe for civil infrastructure. Structural studies employed the direct measurements of surface structures to get the orientations of structures measured. Landsat image and Total Magnetic Intensity (TMI) map of the area was acquired from the Nigerian Geological Survey Agency (NGSA) for subsurface structural analysis. The RTP-TMI (reduce to pole) grid data of the area were processed to improve magnetic anomalies associated with edges of surface/near-surface geological structures using the MAGMAP two-dimensional fast fourier transform (2D-FFT) filters package in Oasis Montaj v7.2 software. Geophysical studies using aeromagnetic data at a near-surface depth of 40 m and fractures measured on the surface both revealed a major trend in the NNE – SSW. It was observed that structures constructed across the major trend suffered little to moderate damage while those constructed along the major fractures trend suffered severe damage. It was concluded that both soils and fractures played individual roles in the collapse of infrastructure in the area.
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