Nature has endowed the earth with glorious wonders and vast resources that man may use for his own ends. Regardless of our want or way of living, there are none that present more variations to our imaginations than the soil which has been of most importance to our ancestors than to our present modern-day world. The soil is the source and destination of mankind, according to great books and also is the bedrock of every building.
The success of any engineering structures depends on the large extent of the nature of the founding soil on which the structures are to be situated. If the bearing capacity of the soil is not good enough to sustain the imposed structure it is bound to fail. The Tropical monsoon climate found in the southern part of Nigeria, it’s influenced by monsoons originating from South Atlantic Ocean which is brought into the country, The tropical monsoon climate has a very high-temperature range and mostly the Southeast receives between 2000-3000mm of rain per year.
Rainfall intensities are usually high and often above 50mm/hr with short interval intensities in excess of 100mm/hr between March till October as this is one of out of much greatest threat to the environmental setting of south-eastern Nigeria is the gradual but constant dissection of the landscape by the soil erosion on water. Furthermore, classical gullies sites are located in false bedded sandstone, coastal plains in locations such as Nanka sands, Bende and Ameki formations in the eastern parts of Nigeria according to research by C.A Igwe on gully erosion in South-eastern Nigeria.
Presently the global climate has not helped issues in this regards, there are various basins and sub-basins in Nigeria’s continental margin indicating different stratigraphic evolution which are attributed due to differences in their standard and tectonic framework.
Soil mapping is only possible because men can examine a profile at one point and successfully predict its occurrence of another point where surface indications are similar. The coastal plains are found in the south-western mostly covered by swampy and mangrove forest merging into the highly degraded forest inland.
According to an extract from the Nigerian journal of technology, in the Ajali formation of Anambra basin specifically the Onyeama mine area Enugu state part of south-eastern Nigeria, it’s predominantly of massive continental deposit overlying marginal sandstones, shale, and coal. It was referred to as the False Bedded Sandstone in the report of Nigeria geological survey, the formation is conspicuous along the Udi plateau and extends continuously in a thin route to the South-East of Okigwe.
A lithological log created along a vertical section implies Sandy CLAY were dominant (Ranging in Silty sandstone, Sandy sandstone, sandy clay-sandy clay, clay, and silty sandstone). The sand encountered at the top is usually good only as subgrade while the clayey sand is poor. Preparations of subgrade for construction usually involves digging in order to remove surface vegetation topsoil and other unwanted materials and to create space for the upper layer of the pavement. Since the sand is a very good subgrade, it would, therefore, undergo lesser compaction processes by being used for construction compared to the clay which would undergo much compaction because it is not a good subgrade.
Rainfall, therefore, plays very significant roles in the erosion hazard of southeastern Nigeria; However, due to the nature of the soil, construction is better done during low intensities of rainfall and it is, therefore, necessary to do removal and replacement, replaced with high-quality fillings to enable a solid construction.
Written by :
Owodunni Abidat Adekemi (B.TECH GEO FUTMINNA)