Engineering Properties of Lateritic Soils around Dall Quarry in Sango Area , Ilorin , Nigeria

The grain size analysis shows that soil sample ADET 1 is silt-clayey, very gravelly sand while sample ADET 2 is gravelly, silt-clayey sand. Atterberg consistency limit test shows that ADET 1 has 40% liquid limit, 18.2% plastic limit, 21.8% plasticity index, 7.4% shrinkage limit and an activity of 0.95 (normal clay). ADET 2 has 46% liquid limit, 23.5% plastic limit, 22.5% plasticity index, 8.2% shrinkage limit and an activity of 0.63. The soil samples are above the activity (A) line in the zone of intermediate plasticity (CL) which means that they are inorganic soils. The samples contain inactive clay suggesting little or no swelling tendency and therefore good for construction material and this would prohibit foundation failure during foundation settlement. The California Bearing Ratio (CBR) values are 1-4 % (average = 2.5%) and 3-5% (average = 4%) in ADET 1 and ADET 2 respectively which means that they are good as sub-grade construction materials. The cohesion ranges from 60-100Kpa (average = 75%) and the angle of internal friction ranges from 3135 with an average of 33.


Introduction
Engineering properties of soils play a significant role in civil engineering construction works particularly in road constructions, foundations, embankments and dams to mention a few.This made imperative, the testing of soil, on which a foundation or superstructure is to be laid.This would determine its geotechnical suitability as a construction material.In recent times, the alarming rate at which lives are being lost due to collapsed buildings and road failures calls for a solution.The solution could be brought by critical geotechnical testing of the engineering soil.The present area is situated within latitudes 8 o 34'N and 8 o 32'N and longitudes 4 o 38'15''E and 4 o 40'E (Figures 1 and 2).The rocks in the study area are mainly granite gneiss and banded gneiss with foliations.
Several authors have worked on the geotechnical properties of lateritic soils.Jackson (1980) reported that lateritic soils have been used successfully as base and sub-base materials in road construction.Vallerge et al. (1969) worked on laterite soil in connection with construction of road, highways and airfields.The engineering problems associated with lateritic soil were evaluated by Lyons et al. (1971).Balogun (1984) reported that the addition of lime to the soil increases its optimum moisture content, liquid limit, California Bearing Ratio (CBR) etc. Alao (1983) studied the engineering properties of some soil samples from Ilorin area and discovered that they could be stabilized by compaction and that the samples could yield maximum strength if they are compacted on the dry side of their optimum moisture content (omc).Ogunsanwo (1989) evaluated CBR and shear strength of some compacted lateritic soils from southwestern part of Nigeria.He reported CBR of 27% in un-soaked and 14% for soaked sample for laterite soils derived from Amphibolites.From mica schist, he   Ogunsanwo (1988) also studied laterite soil from Ojota area in Lagos state and obtained liquid limit of 49.5%, plastic limit of 21.8%, plastic index of 28.4% and linear shrinkage of 6.9%.On the basis of the geotechnical properties, he concluded that the soil is a good engineering construction material.Furthermore, Ogunsanwo (1989) performed CBR and shear strength tests on compacted lateritic soil from Benin sands.He then concluded that the compacted soil samples are suitable for use as sub-base materials in road construction as their CBR falls within the limits specified for this purpose (7-20%).
This paper examines the geotechnical properties around DALL Quarry (a laterite soil quarry) soil in Ilorin, Southwestern Nigeria around where road construction is on-going.

Materials and Methods
Two lateritic soils were sampled (ADET 1 AND ADET 2) and selected for the various testing techniques.Grain-size analyses were performed using the convectional coarse sieve and fine sieve methods.The compaction test was carried out by standard and modified proctor methods.For the standard and modified proctor compaction test, the following materials were used: mould dimension of 10cm by 5cm, weight of rammer=2.5kg,no of layers=5, no of blows=25 but 55 for modified proctor and height of rammer=11.5cm.The CBR tests (soaked CBR test and un-soaked CBR test) are determined using: The analyses were carried out at the Civil Engineering Laboratory, University of Ilorin, Nigeria.

Specific Gravity
The results of the specific gravity analysis of both soil samples, ADET 1 and ADET 2 are 2.68 and 2.63 respectively.Comparing these results with some standard results or values, ADET 1 could be required as sand and ADET 2 could be required as inorganic clay (Bowles 1979).Table 1 presents the typical values of specific gravity of soil particles.

Grain Size Distribution
The test is performed to determine the percentage of different grain sizes contained within the soil.The distribution of different grain sizes affects the engineering properties of soil which in turn influences their usability in construction works.The grain size distribution shows that ADET 1 is silty-clayey very gravelly sand, having 23% silt, 23% clay, 47% sand and 30% gravel compositions.Similarly, ADET 2 could be described as gravelly silt-clayey sand with 36% silt, 36% clay, 52% sand and 12% gravel compositions.

Atterberg Limits
The Atterberg consistency limit tests carried out on the soil samples show that ADET 1 has liquid limit of 40.0%, plastic limit of 18.2%, plasticity index of 21.8%, shrinkage limit of 7.4%, toughness index of 1.16 and activity of 0.95 while ADET 2 it has liquid limit of 46.0%, plastic limit of 23.5%, plasticity index of 22.5%, shrinkage limit of 8.2%, activity of 0.63 and toughness index of 0.82.The plots of plastic index against liquid limit on the plasticity chart show the Atterberg limits plots above "A" and it is in the zone of inorganic clayey silts, clays of low plasticity (CL) for both samples (Figure 3).This indicates Inorganic clays of low to medium plasticity, gravelly clays, sandy clay and silty clay.According to engineering use chart, the soil samples are impervious and inorganic clays useful for erosion resistance in canal constructions.They can also be useful in homogenous embankment in rolled earth dams because of their good to fair workability as construction materials and their fair shearing strength when compacted and saturated (Wagner, 1957).The values of activity (0.95 and 0.63 www.ccsen respectivel in the sam Ogunsanw compacted

Compa
The standa tests result with incre for sample maximum within the There is sl sample AD content is guide to kn and internal friction of 35 o .When compacted at modified proctor, the cohesion is 70Kpa and angle of internal friction is 31 o .The graphical representation is shown in Figures 5-8.The shear box test revealed that the soils are of high strength having cohesion values ranging from 60Kpa to 100Kpa with an average of 75Kpa.Similarly, the angle of internal friction ranges from 31 o to 35 o with an average of 33 o .Alao and Opaleye (2011) obtained an average value of cohesion, 65Kpa and an average value of angle of internal resistance, 26 o .These values show that the soils have high bearing capacity as a result of their respective high cohesion and angle of internal friction values.It can therefore be deduced from the results of the test that the soil samples have a medium angle of internal friction which implies that the soils are hard according to the above references.Hence, the soils could support slope stability and shallow foundation.

Conclusions
Based on the grain size analysis, the soil sample ADET 1 is silt-clayey very gravelly sand (reddish brown colour) with 30% gravel, 47% sand, 23% silt and clay respectively.ADET 2 exhibits reddish brown colour and is characterized by 12% gravel, 52% sand, 36% silt and clay respectively.
Atterberge consistency limit test indicate that the soil samples are above the activity (A) line in the zone of intermediate plasticity clays (CL and there is negligible or no swelling of soils.Therefore they can be chosen as construction materials in buildings and foundations.The CBR values range from 1-5%.This may make it useful as sub-grade materials in road construction and could also be useful for slope stability.
The direct shear test results give an average value of 33 o for the angle of internal friction and average of 75Kpa for cohesion.These values are attributed to the high bearing capacity of the soils making them to be useful in slope stability.The foundation design of the area would be shallow foundation and could also support moderately steep slopes to a great height.
Based on the values obtained from the various tests carried out on the soil samples, it could be concluded that they are good road construction materials and can also be used for slope stability and dam constructions.