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Nigeria, Kaduna State, Kaduna

Geotechnical Mapping of Kaduna and environs

The study area is approximately 625 km2 , which includes Kaduna town at the centre with large settlements like Tudun Nupawa, Kurmin Mashi, Mondo and Rigasa to the west; Kabala and Barnawa to the south; Malali and Unguwan Rimi to the east; and Unguwar Kanawa, Badarawa and Rigachukun to the east. The major river channel is the River Kaduna which cuts the area from west to east. Other rivers are River Gora to the south and River Kura to the north. There are many streams in the area. The topography is virtually flat lying and the relief of the area ranges from 590m and 653m.\r\n The entire project area is underlain by Precambrian migmatite-gneiss complex which constitutes a greater part of the project area; the Pan Africa granitoids which constitute the second largest suit of rocks in the area; and lastly Metasediments/metavolcanics; mostly schists. The soils derived from these rocks are gravelly clays, sandy clays, clays and clayey gravels. Gravelly clays cover about 33% (208km2 ) of the area, sandy clays cover about 6% (37km 2 ) of the area, clays cover about 41% ( 256km2 ) of the area, clayey gravels cover about 6% (37km2 ) and alluvial silty clays cover about 12% (80 km2 ) of the area. \r\n Eight geotechnical factors were evaluated for the project area: soil bearing capacity, soil compressibility, soil expansivity, soil permeability, slope instability, soil erodibility, flooding and soil acidity.\r\nReddish-brown to red, stiff to hard, residual lateritic gravelly clays cover about 33% (208km2) of the study area. They have high bearing capacities at shallow depth, low compressibility, and they are virtually free from highly expansive clays. They are therefore good founding materials at shallow depth. They have medium permeability and they are of low to medium plasticity.\r\nReddish-brown to red, stiff to hard residual lateritic sandy clays cover about 6% (37km2) of the study area. They have high bearing capacities at shallow depth, low compressibility and they are virtually free from highly expansive clays. They are therefore good founding materials at shallow depth. They have medium permeability and they are of low to medium plasticity.\r\nReddish-brown to red, stiff to hard residual lateritic clays cover about 41% (256km2) of the study area. They have high bearing capacities at shallow depth, low compressibility and they are free from highly expansive clays. They are therefore good founding materials at shallow depth. They have low permeability and they are of low to medium plasticity.\r\nReddish brown to red, medium dense to dense residual lateritic clayey gravels cover about 6% (37 km2) of the area. They have high bearing capacities at shallow depth, low compressibility and they are free from highly expansive clays. They are therefore good founding materials at shallow depth. They have high permeability and they are of low to medium plasticity.\r\nGrey to brown, soft to firm, alluvial silty clays cover about 12% (80km2) of the area. They have low bearing capacities at shallow depth. They are therefore not good founding materials at shallow depth, especially for heavy loaded structures. They have low compressibility and they are free from highly expansive clays. They also have low permeability and they are of low to medium plasticity.\r\nThe area is flat lying; there are no slopes or erosion sites which will pose a problem in the study area.\r\nThe streams constitute the main flood paths during the rainy season when they overflow their channels and the flood zones are the flood plains and the fadama areas along Rivers Kaduna, Gora, Kura and their tributaries. Flooding is expected for about 10% (65 km2 ) of the study area.\r\nThe entire soils are slightly acidic (pH = 5 or 6 ). The acidity is not strong enough to course any environmental, agricultural or engineering problem.\r\nA total of six geotechnical maps have been produced: (i) suitable and unsuitable sites for housing estate development map (ii) suitable areas for waste disposal map (iii) potential flood zone map (iv) Land form map (v) structural map and (vi) documentation map.\r\nThe geotechnical map showing suitable and unsuitable sites for housing estate development shows that 79% (495 Km2 ) of the area is suitable for light loaded housing estate development (like simple houses with wall load of up to 100 KN /m and 1 or 2 storey houses with column load of up to 250 KN) because the soils have high bearing capacities at shallow depth, low compressibility and they are virtually free from highly expansive clays. The areas are not susceptible to erosion or flooding. The map also shows that about 21% (130 Km2)of the area is not suitable for housing estate development because the soils have low bearing capacities at shallow depth and the areas are susceptible to flooding. \r\nThe geotechnical map showing suitable areas for waste disposal shows that about 5% (32km2 ) of the area is suitable for waste disposal because the soils have low permeability, the areas are flat lying or slightly elevated and far away from settlements. Water tables are also very low.\r\nThe geotechnical map showing potential flood zones area shows that about 10% (65km2) of the study area is susceptible to flooding because the areas are the flood plains and fadama areas of Rivers Kaduna, Gora, Kura and their tributaries. \r\nThe land form map shows elevated flat lying lands, low lying flood plains, fadama areas and water courses.\r\nThe structural map shows fractures, joints and faults in the study area. \r\nThe documentation map shows the positions of 93 trial pits (TP) dug and 16 drill holes ( BH) drilled on a geological map. \r\n

Inserted in the reports are the following maps (1:50,000): Potential Flood Prone Zones map, Landform map, and Structural map.