Engineering Geological Research – Nigeria Geological Survey Agency

Geotechnical Mapping of Makurdi and its Environs

NG Mod — Wed, 24 Jun 2020 22:37:49 +0000

Executive Summary

The collapse of buildings is a re-occurring disaster in several Nigerian cities for many years, resulting in the loss of lives and properties. This explains the rationale for this project undertaken by the Nigerian Geological Survey Agency with the following major objectives and deliverables:

Produce engineering geological maps which can be used to select areas suitable for:

(i) Housing and industrial estate development etc.

(ii) Waste disposal, cemetery, pit latrines etc.

The methods of study involved field geological mapping, shallow borehole drilling/pitting and laboratory analysis. The field and laboratory geotechnical tests carried include SPT and particle size distribution, hydrometer analysis, Atterberg’s limits, compressibility, permeability, shearbox, PH and bulk density respectively.

The study area is within the latitudes 80 25’ – 80 39’E and longitudes 70 36’ – 70 50’N with a total area of about 625km2 and consists of Makurdi town at the center and parts of four (4Nos) Local Government Areas in Benue State (Makurdi South, Makurdi North, Gwer, and Gwer west Local Government Areas). The drainage system comprises of River Benue and many smaller rivers, and streams. The topography is slightly undulating and the elevation ranges from 70 to 163m above mean sea level. The climate is transitional savannah characterized by a long rainy season (April-October) and a short dry season (Nov. March). And rainfall ranges from 1120-1800mm

The entire project area is mainly underlain by the cretaceous Makurdi and Eze-Aku sand stone Formations.

The soils derived from these rocks were classified in to six (6) soil types according to the British Soil Classification System: sandy clay (CLS), lateritic gravelly clay (CIG), silty clay (CLM), sandy silt (MS) silty sand (SM) and Clay (CI).
The summary of the geotechnical properties is presented below in accordance to the various soil types:

Dark grey to grey, stiff to hard residual sandy clay (CLS).
Medium bearing capacity (150300 kN/m2) at shallow depth, very low compressibility (<0.05 m2/mN), low swelling potential (SP <0.5), intermediate plasticity and low permeability (10-5–10-7m/sec). Very good foundation material at shallow depth.

Dark grey to grey, soft to firm alluvial silty clay (CLM)
Low bearing capacity (qa<150kN/m2) at shallow depth, very low compressibility (<0.05 m2/mN), low swelling potential (SP<0.5), low plasticity and low permeability (10-5–10-7m/sec). Poor foundation material at shallow depth

Dark grey to grey, medium dense to dense residual sandy silt (MS) and silty sand (SM).
Medium bearing capacity (150

Dark grey to grey, stiff to hard residual clay (CI)
Medium bearing capacity (150

The maximum depth of investigation was 5.1m, bearing capacity was found to increase with depth from the depth of 2.5m in all the 16 drill holes, groundwater table was encountered in all the 80 pits and 16 drill holes and all the side walls of the pits and drill holes were not very stable.

The soil geotechnical properties (bearing capacities, permeability and soil types) together with the location co-ordinates were linked to Arc-view Geographic information system (GIS) soft wire to produce the following land-use maps:

i. Foundation soil map

ii. Soil bearing capacity map

iii. Soil permeability map The foundation soil map shows that the map is divided into six (6) portions according to the six (6) soil types: MS, SM, CI, CLS, CIG and CLM.

The bearing capacity map shows that the map is divided into 3 portions; low bearing capacity (qa>150kN/m2), medium bearing capacity (150300kN/m2) portions.

The permeability map shows that the map is divided in to two portions: low permeability (10-5–10-7 m/sec) and medium permeability (10-3 – 10-5 m/sec) portions.

The soil foundation, bearing capacity and permeability maps can be used at the preliminary stage to locate suitable sites for housing/industrial estate developments, other lightly loaded civil engineering structures, waste disposal sites, cemetery, pit latrines etc.

Geotechnical and Engineering Geological Investigation of Owerri and Its Environs

NG Mod — Wed, 24 Jun 2020 22:24:12 +0000

Executive Summary

The geotechnical and engineering geological investigation of Owerri and its environs had been studied. The project covered an area of 625km2 encompasses Owerri and environs. The focus of the research was to investigate the subsoil in order to determine its engineering properties, its suitability as foundation for industrial and residential houses. It was also aims at sourcing suitable building materials for road embankments, earth dams and leeves and to select and design suitable shallow foundations of structures.

The study involved collection of seventy (70) bulk soil samples from test pit soil at a depth of 1.5m for determination of California Bearing Ratio (CBR), Atterberg Limits and grain size distribution test. Standard Penetration test (SPT) test was done on sixteen (16) boreholes to a depth of 10m and undisturbed samples collected at depths of 1.5m, 4.5m and 7.5m in each hole for Standard Penetration test (SPT) for the determination of the bearing capacity of the soil from triaxial test.

The result of the California Bearing Ratio (C.B.R) for the soaked samples showed that the values varies from 3% to 6%. These values fall below the Nigerian General Specification for Roads and Bridges (1997) that states that soil for sub-grade, sub-base and base material should not be less than 15%, 30% and 80% respectively. Therefore, the soils in the study area are not suitable for sub-grade, sub-base and base materials, unless the soil is improved through soil improvement measures.

The result of the Atterberg Limits and grain size distribution of the soil samples showed that ninety-three (93%) of the samples belong to the clayey sand of low plasticity (SC) class, while three (3%) and three (3%) respectively belongs to the sandy clay of low plasticity (CLS) and silty sand of low plasticity (SM) class based on Unified Soil classification scheme. The result also showed that the samples contain relatively high amount of fines, which can contribute to some level of instability of the soil. In terms of strength, these soils have medium strength that can support housing estate development. Improved stable foundations on these soils can 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 can be adopted.
T
he result of the permeability test from sieve analysis showed that the coefficient of permeability of the soils varies from 8.1 x 10-5 to 1 x 10-4 cm/s. These values indicate that all the soil in the study area falls within the medium coefficient of permeability class of Terzaghi and Peck, 1967, Kulhawy and Mayne, 1990 and Ele Engineering Geology classification. These values indicate that the soil have good drainage characteristics. These soils are not be suitable for construction of sanitary landfill, core of earth dam, recharge pit, location of underground mines or good site for burial ground, because of their permeability characteristics. However, they are generally suitable for the shell of an earth dam.

The bearing capacity values of the soils vary from 300.75 KN/m2 to 664.89 KN/m2. Ninety-one (91%) and ten (10%) of the soil samples respectively fall within the high and medium bearing capacity of the Nigerian General Specification for Roads and Bridges (1997). Therefore, majority of the soil in study area are suitable for housing estate development in terms of their bearing capacity.

However, majority of the soil are erodible, excavatable, very loose to loose, friable, dispersive and poorly consolidated. These characteristics made them to be susceptible to flooding and erosion.

Geotechnical Mapping of Benin City and Its Environs

NG Mod — Wed, 24 Jun 2020 21:59:01 +0000

Executive Summary

Building collapses have become a recurring incidence in many parts of Nigeria.In view of contributing to the forestalling of future occurrences, the Nigerian Geological Survey Agency (NGSA) as part of its statutory role had embarked on a systematic Geotechnical mapping of the major cities in Nigeria. This is aimed at providing relevant geotechnical information that would aid in mitigating these problems.The project area, Benin City and its environs, is the capital of Edo State located in the south-southern part of Nigeria. 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 298Benin 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 IkhueNiro, Ute, Obanyator, Etete, Utoka,Ahor, etc.

The study area is underlain by the coastal plains sands of the Niger Delta region of the country.The project primarily involved soil sampling at various depths within a total area coverage of 625km2. Soil samples were collected from pits dug to 1m and from boreholes drilled to 6m.

Samples collected were analysed in the labaoratry 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.

Percentage 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 10-7to 4.80 x 10-4 which is very low.Maximum Dry Density ranged from 1756kg/m3 to 2078kg/m3. Shear strength ranged from 91.3 kPa to 170 kPa. Areas suitable for location of waste disposal sites covers about 38% and about 25% is suitable for development of housing estates.

Geotechnical / Engineering Geological Mapping of Sokoto and Its Environs

NG Mod — Wed, 24 Jun 2020 21:25:04 +0000

Executive Summary

The geotechnical/ engineering geological mapping of Sokoto and Its environs is a positive step of the Nigerian Geological Survey Agency to attempt to address the present problems of foundation and other structural failures rampant in the burgeoning Nigerian cities. It will also generate data bank of the geotechnical properties of soils in all the big towns in Nigeria for future land use planning and expansion. The project area is enclosed by Latitudes 12̊ 57′ and 13º 11’N and Longitudes 5º 08′ and 5º 22’E. It measures approximately about 25km by25km i.e. about 625km2 in area.

Geologically, Sokoto and its environs fall within the sedimentary formations of the South Eastern extension of the Illumeden Basin which has its centre in the Niger Republic.The project area is underlain by the Eocene Gwandu Formatiion, the Palaeocene Kalambaina and Dange Formations, the Maastichtian Wurno, and Maastrchtian/Lower Cretaceous Wurno/Taloka Formations.

The geotechnical mapping focused primarily on the geotechnical properties of the soils derived from these geological formations down to the depth of 10m. Out of the 100 cells to which the area was grided, 82 test pits were dug each to a depth of 1.5m and the soil profiles studied and documented. Sixteen (16) Bore Holes were drilled and Standard Penetration Tests recorded at predetermined depths. Dutch Cone Penetrometer Tests were also carried out close to each of the 16 bore holes.

Two Engineering Services Companies – Kabia Laboratories Ltd based in Abuja and ADIBEKS Engineering Services based in Kaduna drilled the bore holes and also analysed the soil samples from the project area.

The results of the field soil profile study and the laboratory tests have indicated that:

(I) The excavability of soils in some parts of the project area can be quite difficult because of the lateritic boulders and cobbles within the soil.

(II) Lateritic overburden can be as thick as 3 to 5m in some localities in the project area.

(III) Stiff platy grey shale or marly and crystalline limestone may underlie the lateritic overburden in most places.

(IV) From the ground level (0m) to 0.5m, the soil can be moist, grayish brown with rootlets and worm burrows. Down to 1.5m, the soil becomes greyish, compact, with firm plastic clay and a lot of phosphatic nodules (characteristic of soils derived from the Kalambaina and Dange Formations).

(V) For soils derived from the Wurno/Taloka Formation, the soil varies from yellowish brown at the top to moist, reddish brown, intact,cohesive homogenous sandy clay down to 1.5m in the trial pits.

Two types of soil samples were collected for laboratory analyses:
Bulk Test pit samples (collected at 1.5m) and standard penetration test samples (SPT) (collected at specified depths) down the bore hole.

The acidic/alkaline tests performed on the 48 test pit samples in the field, indicate that near surface soils are slightly acidic but more alkaline down into the ground.
The results of Grain size distribution and Atterberg Limits tests used in soil classification showed that under the American Association of State Highway and Transportation Officials (AASHTO) the soils in the area classify as A-2-4, A-4, A-7-5, and A-7-6.
On the Unified Soil Classification System (USCS) all the soil samples classified as CL.
On the Modified Plasticity Chart for use with USCS,all the soil samples plotted above the ‘A’-Line and left of the 50% Liquid Limit line.

The bulk density of the sub-soil ranges from 1.30g/cm3 (BH 26) to 2.23g/cm3 (BHs 95,97) whereas their natural moisture content varies from 2.0% (BHs 22,95,97) to 23% (BH 26 @ 1.5m).

The maximum dry density of the compacted soil varies from 1.41g/cm3 to 2.0g/cm3 while the optimum moisture content(omc) varies from 11.0% to 28.0%
The consolidation test results showed a material of LOW compressibility. From the tests carried out, 50% consolidation occurred within 4minutes indicating immediate settlement upon application of load which is due to the fine nature of the dominantly silty sandy material.

Linear shrinkage test results showed a zero shrinkage for the dominantly silty sand and a shrinkage of 1.35% to 12.6% for the silty clay materials.
Bearing capacity values were computed based on the Standard Penetration Test (SPT), Cone Penetration Test (CPT) and laboratory Triaxial Compression test.
Results from SPT tests at Bore Hole locations IFS 9, 22, 50, 63 and 97 gave N-values of between 1-5, 3-48, 8-78, and 9-100 with corresponding calculated corrected N-values (N1) of between 1-15, 3-32, 8-47 and 16-58 for 0.5m, 1.5m, 3.0m and 4.5m depths respectively. All Boreholes mentioned above terminated at 4.5m depth, except Boreholes IFS 26 which terminated at 6.0m and IFS 97 that ended at 7.5m depths. Bearing capacity values for all the Boreholes ranged between 56KN/m2 and above 500KN/m2 at between 0.5m – 7.5m depth.

Bearing capacity computation based on the laboratory. Triaxial Compression Test gave values of between 180KN/m2 to 705KN/m2 at 1.5m depths and between 356KN/m2 to 1114 KN/m2 at 3.0m depths.

In the Cone Penentrometer Test, the allowable Bearing Capacity ranged from 29KN/m2 (BH 2) to 400KN/m2 with average value of 83.9KN/m2

The results of the California Bearing Ratio indicate that soils classified as A-2-4 gave CBR of as much as 24%, but A-7-5 and A-7-6 soils have CBR values of between 3 and 5%.

In designing for a building, the bearing capacity of 29KN/m2 the CPT will be employed for shallow foundations. i.e Strip Footing.

Both the field in-situ and laboratory tests have shown that the soils of the project area conform to standards for good sub-base and sub-grade materials for highway construction.

For the construction of buildings, the foundation depths (Df) should not be less than 1.5m below finished ground level. But for high rise or multistory building requiring pressures in excess of those recommended for strip/square footing, raft footing may be employed. To check the possible adverse effect of swelling and shrinkage by the soil / underlying shale, iron wire guaze should be laid in the foundation before blinding with a rich dense mix of Portland cement concrete.

Geotechnical and Engineering Geological Investigation of Aba, Abia State and Its Environs

NG Mod — Wed, 24 Jun 2020 21:21:11 +0000

Executive Summary

The phenomenal rise in the number of reported cases of collapsed buildings in the country with its attendant loss in revenue and human lives has been a cause for concern to well-meaning Nigerians. As part of its constituted mandate, the Nigerian Geological Survey Agency in 2006 commenced a systematic engineering geological mapping of selected state capitals and major urban centres. In 2007, this exercise was extended to Aba and its environs.
The objective of this project is to determine the following:
(i) type, physical, and engineering characteristics of the subsoil,
(ii) suitability or otherwise of the subsoil for foundation of civil structures,
(iii) Depth to bedrock, if any, and groundwater conditions.

Fifty four bulk samples were taken from test pits dug to a minimum depth of 1.5 metres for Atterberg Limits Test, Grain Size Distribution analysis, Compaction, and California Bearing Ratio determination.

Twelve shell and auger boreholes were drilled using the Pilcon Wayfarer 1500 percussion rig. The boreholes were advanced to 10 metres depth. Undisturbed samples were collected in Shelby tubes at selected intervals of 1.5metre from each other for Triaxial Compression Test, Consolidation test and Grain Size Distribution analysis.

Twelve Dutch Cone Penetrometer Sounding Tests were carried out at 10 metres depth or to refusal. The resistance of the soil was measured by means of a dial guage attachment to the penetrometer machine. Readings obtained and the graphical plots of the soil resistance were used to determine the allowable bearing pressure of the soil.

Results of the grain size distribution analysis show a consistent increase in grain size with increasing depth. The soils classify as very fine sands, silty to clayey fine sands, or clayey silts with slight plasticity (ML), and gravelly clays, sandy and silty clays (CL) according to the Unified Soils classification scheme (USC).They have good to poor, and good to fair compaction characteristics respectively. They show high compressibility, moderate permeability and are excavatable and stable as fill material, but would be unsuitable as base course.

Their bulk density showed a range from 1.95Mg/m3 to 2.19 Mg/m3, their natural moisture, a variation from 12% to 21%, while their optimum moisture content ranges between 9.5% and 19.8%. Cohesion values range from 28 kN/m2 to 60 kN/m2, and maximum dry density ranging between 1.09 Mg/m3 and 2.17 Mg/m3 were recorded. The soaked and unsoaked California Bearing Ratio (CBR) values of 5.1% to 11.2% and 7.6%to18.9% were registered respectively. No ground water was encountered during the operation.

For design of strip/square footing 1.5metres wide founded at 1.5metres depth, the average allowable bearing capacity of soil would be 25 kN/m2 from cone, while the sleeve gives 50 kN/m2, allowing maximum differential settlement of 25mm (1 inch), using a factor of safety of 3.

For the same footing, under same conditions, the average allowable bearing capacity would be 125 kN/m2 for Standard Penetration Test, while the average allowable bearing capacity of 279 kN/m2 was computed for same footing under same conditions from the Undrained Triaxial compression Test. Therefore, it is recommended that the Dutch Cone Penetration Test average bearing capacity of 25 kN/m2 be used for design. However, it must be ensured that no ingress of water be allowed into the foundation. Alternatively, a raft foundation may be necessary for design. If a pile foundation is adopted, it must be imperative to carry out a pile loading test.

Geotechnical Mapping Of Enugu Metropolis And Environs

NG Mod — Wed, 24 Jun 2020 17:38:53 +0000

Executive Summary

The geotechnical survey of Enugu metropolis and its environs was carried out. The area covers approximately 625km2 and includes parts of Udi, Enugu metropolis, Oliemba, Emene and Ukana. The topography of the area is rugged with the Enugu Escarpment as a prominent feature. East of the Escarpment are Rivers Ekulu, Asata, Iyaka, Nyaba and Nvenen dissecting the area and flowing into the Cross River system.
The area is underlain by the following Cretaceous rocks: the Agbani Sandstone, the Enugu Shale, the Mamu Formation and the Nsukka Formation. There is also alluvium deposit of Quaternary to Tertiary age.

The soils derived from the Enugu Shale and the Mamu Formation are stiff and have swelling characteristics while those derived from the Agbani Sandstone and the Ajali Formation are loose and more permeable.

The predominant geotechnical factors observed in the area are: Problem soils, inundation, slope instability and acidity problems.

Problem soils are mainly those derived from the Enugu Shale, the Mamu Formation and the Alluvium deposits along the flood plains of Rivers Iyaka, Ekulu, Asata, Nyaba and Nvenen. Approximately 42% of the study area is covered by problem soils.

Slope stability problems occur along the scarp of the Enugu escarpment, especially the area underlain by the Ajali Formation. About 17.4% of the total study area is affected by slope instability. Inundation occurs along the banks of down streams of Rivers Iyaka, Ekulu, Asata, Nyaba and Nvenen. Approximately 0.07% of the total area is affected by inundation. Soils with acidity problems cover about 92.5% of the study area. These are areas underlain by the Enugu Shale, The Mamu and the Ajali Formations.

Remedial measures that are suggested when developing on the problem soils include: Provision of foundations as deep as 1.5m or more to avoid the zone of volume change, isolating the foundation below ground level from the surrounding soil by various means such as two coats of bitumen or polythene liners to minimize friction between the foundation and the soil, sand-filling the foundation to a height of 30cm before laying the sand Crete blocks on top to avoid friction between the foundation soils and the block work, using ordinary Portland cement not less than 400kg /m³, water/cement ratio of 0.5 for soils with pH less than 5 and carrying proper study of slope instability before construction or avoiding all areas of active slope failures during development on those areas.

Geotechnical Mapping of Maiduguri and its Environs

NG Mod — Wed, 24 Jun 2020 17:25:12 +0000

Executive Summary

The project area is bounded by latitudes 110 41’ 30” to 120 00’ 00”N and longitudes 130 00’ 00” to 130 44”E and covers an area of 1,118 Km2. The area covers three local governments; Maiduguri, Jere and Konduga local government areas. Maiduguri town, the capital of Borno State is at the centre. The topography of the area is virtually flatlying, with visibility possible to several kilometers. It has an average elevation of 315m above sea level.

The area is within the semi-arid climate region and temperature varies from 25 to 360c seasonally. The area is characterized by a long dry season (October-May) and short rainy season (November-April) and the rainfall varies from 330 to 1020mm. The area is Generally drained by River Ngadda which has its sources from southern Borno.

The project area falls within the south-western part of the Chad Basin and is wholly underlain by Chad formation, a sequence of lacustrine and fluviatile clays and sands of pleistocene age. The top soils covering the study area within the depth range of 0-1m consist of very loose to loose slightly clayey silts covering 49% (548 Km2) of the area, very loose to loose slightly sandy silts covering 31% (346 Km2 ) of the area, soft silty clays covering 12% (134 Km2) of the area and firm to stiff slightly silty clays covering 8% (89 Km2) of the area.

Four different soil types between the depths of 1 and 2 m covering Maiduguri and its environs, which were derived from the Chad formation, have been identified and mapped because of their importance as foundation soils for light-loaded structures and as a link between the top soils and the soils at depth. The four soils mapped consist of medium dense clayey silts covering about 76% (850 Km2) of the area, firm silty clays covering about 12% (134 Km2) of the area, stiff slightly silty clays covering about 8% (89 Km2) of the area and medium dense silty sand covering 4% (45 Km2) of the area.

Five geotechnical factors were evaluated for the project area; soil bearing capacity, soil expansivity, soil compressibility, soil permeability, and soil acidity.

The clayey silts, the silty sands and the silty clays are of low bearing capacities at shallow depth (<1m) and high bearing capacities at depth (>1m); while the slightly silty clays have high bearing capacities even at shallow depth. This makes the silty sands, clayey silts, and silty clays bad founding materials at shallow depth (<1m) but good founding materials at depth (>1m). The slightly silty clays are good founding materials even at shallow depth because of their high bearing capacities, low compressibility and low swelling potential.

The silty and slightly silty clays of this area are of low swelling potential and inactive. The silty clays are of high compressiblities at shallow depth (<1m) and low to very low compressibilities at depth (>1m); while the slightly silty clays have low to very low compressiblity even at shallow depth.

The high compressibility of the silty clays at shallow depth is responsible for the structural and architectural distress of many residential buildings at Bulunkutu Abuja area of Maiduguri town. These occurred due to excessive differential settlements of the buidings in the silty clays.

The low to very low permeability of the clayey silts, silty clays and slightly silty clays make the soils very much suitable for sitting waste disposal, cemetery and pit latrine sites, while the medium permeability of the silty sands makes the soil not suitable.

The soils in the study area are slightly acidic with a pH range of 5-7. The acidity is not strong enough to cause any environmental, agricultural and engineering problems. Therefore, ordinary Portland cement could be used for foundations in the soils.

The percentage area of coverage, which is 8×10-6 %, is too small to give realistic values of the engineering properties of the soils in the area considering the heterogeneous nature of soils. However, the properties being presented can be used as first approximation of the likely values of the engineering properties of the soils tested. This will give a general over-view of the engineering properties of the soils in the area investigated. For specific sites, comprehensive site investigations must be carried out.

Geotechnical Mapping of Kaduna and its Environs

NG Mod — Tue, 23 Jun 2020 06:32:17 +0000

Executive Summary

The collapse of buildings and flooding are re-occurring disasters in several Nigerian cities, including Kaduna, for many years, resulting in the loss of lives and properties. This explains the rationale for this project undertaken by the Nigerian Geological Survey Agency with the following major deliverables and objectives:
Production of Geotechnical maps showing:
Areas suitable and unsuitable for housing projects,
Areas suitable for waste disposal and
Areas susceptible to flooding.

The method of study involved field geological mapping, shallow borehole drilling/testing and laboratory analysis. The laboratory geotechnical tests carried out on the soils included: particle size distribution, Atterberg limits, unconsolidated undrained triaxial, compressibility, permeability, shear box and pH.

The study area is approximately 625km2, which includes Kaduna town and large settlements comprising Tudun Nupawa, Kurmi Mashi, Mando and Rigasa to the west; Kabala and Barnawa to the south; Malali and Unguwan Rimi to the east; and Unguwar Kanawa, Badarawa and Rigachikum to the north. The major river channel is River Kaduna which flows from west to east. Other rivers include River Gora to the south and River Kura to the north. There are also many smaller streams in the area. The topography is generally flat and the elevation ranges from 590 to 653m above mean sea level. As a result of the flat topography, there are no gully erosion and slope instability problems.

The entire project area is underlain by Precambrian migmatite-gneiss complex which constitutes the largest portion of the area followed by the Pan African granitoids (the second largest) and lastly, the metasediments/metavolcanics which are 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, about 6% (37 km2) clays about 41% (256 km2), clayey gravels about 6% (37/cm) and alluvial silty clays, about 12% (80 km2).
The geotechnical and physico-chemical properties of the various soil types are presented below:

Reddish-brown to red, stiff to hard, residual lateritic gravelly clays and Reddish-brown to red, stiff to hard residual lateritic sandy clays.
Low to medium plasticity, low compressibility, (<0.1 m2/MN), medium permeability (10-3 – 10-5m/s), very low to low swelling potentials, and high bearing capacities (>150 kN/m2) at shallow depth. Good foundation materials.

Reddish-brown to red, stiff to hard residual lateritic clays.
Low to medium plasticity, low compressibility (<0.1 m2/MN), low permeability (10-5 – 10-7m/s), very low to low swelling potentials, and high bearing capacities (>150 kN/m2) at shallow depth. Good foundation materials.

Reddish brown to red, medium dense to dense residual lateritic clayey gravels.
Low to medium plasticity, low compressibility (<0.1 m2/MN), high permeability(>10-3m/s), very low to low swelling potentials, and high bearing capacities (>150 KN/m2) at shallow depth. Good foundation materials.

Grey to brown, soft to firm, alluvial silty clays.
Low to medium plasticity, low compressibility (<0.1 m2/MN), low permeability (10-5 – 10-7m/s), very low to low swelling potentials, and low bearing capacities (<150 KN/m2) at shallow depth. Poor foundation materials.
The soils in the study area can generally be classified as CIG, GCL and CLS according to the British system of soil classification and as GC and SC according to Unified Soil Classification system.
The 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 affects about 10% (65 km2) of the study area. The entire soils are slightly acidic (pH = 5 or 6) and therefore do not pose any serious engineering, environmental or agricultural problems.
The soil geotechnical properties and the topography were jointly used to produce the following land use maps showing areas:
i. Suitable for housing estate development (about 79% of study area).
ii. Suitable for waste disposal (about 5% of study area).
iii. Susceptible to flooding (flood risk areas) (about 10% of study area).
iv. Indicating different landform types.

Engineering Geological Mapping of Gombe and its Environs

NG Mod — Tue, 23 Jun 2020 06:11:14 +0000

Executive Summary

The result of the permeability test from sieve analysis showed that the coefficient of permeability of the soils varies from 8.1 x 10-5 to 1 x 10-4 cm/s. These values indicate that all the soil in the study area falls within the medium coefficient of permeability class of Terzaghi and Peck, 1967, Kulhawy and Mayne, 1990 and Ele Engineering Geology classification. These values indicate that the soil have good drainage characteristics. These soils are not be suitable for construction of sanitary landfill, core of earth dam, recharge pit, location of underground mines or good site for burial ground, because of their permeability characteristics. However, they are generally suitable for the shell of an earth dam.

However, majority of the soil are erodible, excavatable, very loose to loose, friable, dispersive and poorly consolidated. These characteristics made them to be susceptible to flooding and erosion.