The project area is defined by longitudes 005º 30' and 005º 45'E and latitudes 6º 15' and 6º 30'N with a total area of approximately 625km2. The area lies within 1:50,000 Sheet 298 Benin City N.W. The area cuts across four Local Government Areas namely Oredo, Egor, Ikpoba Oka and part of Uhunmwonde. The main town in the area is Benin City. Other settlements include Ikhue Niro, Ute, Obanyator, Etete ,Utoka, Ahor, etc.\r\n\r\nThis was aimed at providing relevant geotechnical information that would aid in mitigating the problem of building collapse. \r\n\r\nThe study area is underlain by the coastal plains sands of the Niger Delta region of the country. \r\n\r\nSoil samples were collected from pits dug to 1m and from boreholes drilled to 6m. Samples collected were analyzed in the laboratory for soil acidity, particle size distribution, Atterberg limits, Triaxial Compression. In-situ Standard Penetration testing was carried out in boreholes drilled at sixteen locations. Samples were collected from the boreholes at 1.5m intervals for Consolidation test. \r\n\r\nPercentage fines ranged from 12.10% to 57.50%. Soils were classified as clayey, silty sand. Liquid limit ranged from 21.50% to 47.50%, Plasticity Index ranged from 3.40 to 24.20 while Shrinkage Limit ranged from 7.70 to 15.30. The soils showed no swelling potential and are highly erodible. The soil pH ranged from 4.36 to 5.42, Specific gravity ranged from 2.61 to 2.76 and dry unit weight ranged between 417.40g to 473.50g. Permeability ranged from 6.82 x 10-7 to 4.80 x 10-4 which is very low. Maximum Dry Density ranged from 1756kg/m3 to 2078kg/m3. Shear strength ranged from 91.3kPa to 170 kPa. Areas suitable for location of waste disposal sites covers about 38% and about 25% is suitable for development of housing estates.Determination of in-situ soil conditions

Determination of in-situ soil conditions

Thirty-seven (37) bulk samples taken from a depth of 1.5 meters were analyzed for the determination of Atterberg Limits, Linear Shrinkage, Grain Size Distribution, compaction, and California Bearing Ratio (CBR).\r\n\r\nSixteen (16) borings were made to a depth of 10 meters or to refusal. Standard Penetration Test (SPT) was carried out at every 1.5 meter depth interval and undisturbed samples were collected at the same depth or change of material for Triaxial Compression Test, Grain Size Distribution analysis, and Consolidation. All boreholes stopped at between 1.1m and 5.3 m except borehole 16, cell 056 at NYSC Zonal Office, which went to a maximum depth of 10 meters. \r\n\r\nTen (10) Dynamic Cone Penetrometer (DCP) tests were carried out using a 25mm thin walled pipe with 600 cone. Due to the fine grained nature of the dominantly clayey material, particle size distribution analysis by hydrometer method was employed.\r\n\r\nResults of field and laboratory tests reveal that the entire area on the average is overlain by a 2.5m thick sand, silt, and clay, with spot clay deposits notably at cells 056 (NYSC Zonal office) and 047 (Railway quarters). Soils of Gombe can be classified into nine groups, A-3, A-4, A-5, A-6, A-7, A-1-b, A-2-4, A-2-6, and A-2-7. Of the 37 samples analyzed, 18 are sands and hence non-plastic, 2 are silts and plotted below the A-line on the plasticity chart, while17 others are clays and plotted above the A-line.\r\nResults of SPT tests at cell 001 to 060 gave blow count (N) values of between 2 and 100 with calculated corrected N-values (N?) of between 2 and 58, at 0.5m, 1.5m, 3.0m, with maximum depth of 10m at NYSC Zonal Office. Apart from the boring at NYSC Zonal office, all borings terminated at between 1.1m to 5.3m.\r\nFrom the bulk samples recovered at 1.5m depth, bearing capacity computations based on Triaxial Compression test gave values between 277kN/m2 and 2545 kN/m2. \r\nConsolidation test results show that the materials are of medium to high compressibility. About 90% consolidation occurred within 40-120 metres, indicating secondary settlement upon application of load. The 24-hour soaked California Bearing Ratio (CBR) values between 5.1% and 11.2% shows the materials are good to be used for road subgrade. Values of maximum Dry Density (MDD) ranging between 1.09Mg/m3 and 2.17Mg/m3 with optimum moisture content (OMC) ranging from 9.5% to 19.8% were recorded. Linear shrinkage test shows low shrinkage for the sandy material, and shrinkage of up to 14% for the dominantly clayey materials. \r\n\r\nCivil constructions in Gombe require strict adherence to building standards and the findings of this work in the light of the thick clay that underlies most part of the state capital. This can go a long way in reducing incidence of multiple cracked buildings that are scattered all over the area. \r\n

Determination of in-situ soil conditions

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

Determination of in-situ soil conditions

Determination of in-situ soil conditions

Reported cases of collapsed buildings have become a common feature of our daily news. The failure of these infrastructures has resulted to huge losses in revenue and human lives. \r\n\r\nThis project which covers an area of 625km2 encompasses Owerri and environs. \r\n\r\nThe objective of this project was to investigate the subsoil in order to determine its engineering properties, its suitability as foundation for industrial and residential houses. Additionally, it aimed at sourcing suitable building materials for road embankments, earth dams and leeves, and to select and design suitable shallow foundations of structures. The causes of development of cracks and collapse of buildings will also be determined and possible preventive measures proferred.\r\n\r\nSeventy-one (71) test-pit bulk samples were taken for the determination of California Bearing Ratio (CBR), Atterberg Limits, and grain size distribution. Sixteen (16) boreholes were drilled for Standard Penetration test (SPT) and Ten (10) Cone Penetrometer Tests (CPT) were carried out. \r\n\r\nGeophysical method was also employed to assess the presence of any incompetent layer like clay, which could expand or shrink due to application or removal of moisture. Unacceptable degree of expansion or shrinkage affects the foundation, thereby causing the development of cracks. \r\n\r\nResults of laboratory analyses show that the soils can be classified as clayey gravel (GC), clayey sand (SC) and silty sand(SM). They are found to be highly permeable.\r\nTriaxial test results show that the soils have cohesion values ranging from 20KN/m2 in borehole 6, to 75 KN/m2 in borehole 9.\r\nCompaction test recorded maximum dry density (MDD) values ranging from 1.64 Mg/m3 to 1.75 Mg/m3 in boreholes 2 and (1,3,7,8) respectively.\r\nSoil strengths of 301KN/m2 to 621KN/m2 were recorded in boreholes 6 and 12 respectively. The presence of gravels imparted high strengths, low compressibility, poor consolidation, though the dominance of clayey sands and fines lowers the bearing capacity. The predominance of the fines is also responsible for the degree of instability witnessed. Their California Bearing Ratio (CBR) values are low, from 3 to 6, requiring that soil-improvement measures would be necessary for stable structures.\r\n\r\nThe soils are erodible, excavatable, very loose to loose, dispersive, and moderately plastic, thereby leading to significant deformation under load. Inundation caused critical changes in soil strength, consolidation characteristics, and bearing capacity. The influence of these changes manifested in somewhat excessive settlement and foundation failure. No serious slope instability problem existed.\r\nDynamic rollers used by road construction companies generated vibrations through the foundation, thus increasing the stresses in the ground. As the stresses exceed the soil strength, failure in form of cracks occurs.\r\n\r\nStable foundations could be achieved through compaction of the material prior to construction, and by increasing foundation width and depth. Reinforcing steel can also be added to foundation, while soil improvement measures are adopted.\r\n