Estimating Compaction Characteristics from Fines in A-2 Type Lateritic Soils

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1 Research Journal of Environmental and Earth Sciences 3(4): , 2011 ISSN: Maxwell Scientific Organization, 2011 Received: March 22, 2011 Accepted: April 20, 2011 Published: June 05, 2011 Estimating Compaction Characteristics from Fines in A-2 Type Lateritic Soils F.C. Ugbe Department of Geology, Delta State University, Abraka, Nigeria Abstract: This study is aimed at quantitatively relating percent fines to compaction characteristics in lateritic soils. Lateritic soils of western Niger Delta are the major construction material and consequently requires compaction test before utilization. Fines have profound influence on the compaction characteristics of these soils. Both compaction and particle size distribution tests were carried out on sixty eight (68) samples. Compaction characteristics values were plotted against fines percent and different predictive models obtained. Thirty (30) new samples were obtained within the region and compaction and particle size distribution tests carried out. Validation of the models using field data yielded correct prediction of 92 and 93% for maximum dry density and optimum moisture content respectively. Key words: Compaction, correlation coefficient, fines, Niger Delta INTRODUCTION The study area is part of the western Niger Delta with longitude 06º13!00" to 06º30!00" E and latitude 05º49!00" to 06º30!00" N (Fig. 1). The geology of Niger Delta has been described by various researchers (Short and Stauble, 1967; Allen, 1965; Reijers et al., 1996; Weber and Daukoru, 1975). Lateritic soils are quite extensive in the Niger Delta occurring in the dry flat plains of the region. Figure 2 indicates the geomorphological units of the Niger Delta with the dry flat plains occurring both in the western and eastern Niger Delta (Allen, 1965). Various researchers have established A-2 type (AASHTO classification) lateritic soils as the dominant soil group in the dry flat plains of Niger Delta (Arumala and Akpokodje, 1987; Alabo et al., 1983; Ugbe, 2009). Akpokodje, (1987) postulated that fines percent influences compaction characteristics in lateritic soils within Niger Delta. These soils are the major road construction material within the region and consequently requires compaction test. Compaction test is the most common soil improvement method. Compaction of a soil is defined as the process whereby soil particles are constrained to pack more closely together through mechanical compression leading to a reduction in air voids (Road Research Laboratory, 1952; Rahn, 1996). Compaction test requires appreciably large quantity of bulk sample. Such samples are sometimes difficult to obtain in western Niger Delta especially during the wet season because of the inaccessibility of such terrains. One way to overcome this problem is to predict compaction characteristics from simpler geotechnical test that require relatively smaller quantity of samples. Johnson and Shallberg (1960) have estimated compaction characteristics through approximate methods without recourse to the conventional compaction test. Winterkorn (1967) employed granulometric principles to predict compaction characteristics for granular soils. Kofiatis and Manifopoulous (1982) developed a parametric relationship for predicting the maximum dry density of granular soils. Omar et al. (2003) developed models for the prediction of compaction characteristics from simpler geotechnical tests on granular soils from United Arabs Emirates. No study has so far been carried out to predict compaction characteristics from a simple particle size distribution test of lateritic soils within the Niger Delta region. The study is therefore aimed at attempting a quantitative relationship between percent fines and compaction characteristics of the lateritic soils. Attempts are also made to develop predictive models that may estimate compaction characteristics of lateritic soils without going through the laboratory conventional compaction test procedures. MATERIALS AND METHODS The soil samples were collected between 1 st September and 1 st October The area covers parts of Edo and Delta States of Nigeria. The area is accessible from Benin, Warri and Asaba (Fig. 1). Sixty-eight (68) soil samples were initially obtained from the region. The soil samples were first air dried for fifty days before subjecting them to particle size 433

Compaction characteristics (Maximum Dry Density (MDD) and Optimum Moisture Content (OMC)) values and fines percent are presented in Table 1. Figure 3 indicates the particle size distribution curve.

2 Fig. 1: Study location map Fig. 2: The major geomorphic units of the Niger Delta (Adapted from Allen, 1965) distribution and compaction tests in accordance with British Standard procedures BS1377 (1990). Compaction characteristics (Maximum Dry Density (MDD) and Optimum Moisture Content (OMC)) values and fines percent are presented in Table 1. Figure 3 indicates the particle size distribution curve. The results in Table 1 were then plotted as compaction characteristics (MDD and OMC) against fines percent with model equations developed (Fig. 4 and 5). Thereafter, thirty other different samples within the region were collected (Table 2) and subjected to the same tests as the earlier sixty-eight samples to validate the models developed. The values of the fines percent for these new thirty samples were plugged into the estimation models to determine the compaction characteristics. The measured compaction characteristics were then plotted against the estimated compaction characteristics and the correlation coefficient determined (Fig. 6 and 7). 434

3 Fig.3: particle Size Distribution Curve of Soils of Study Area (A-2type) Table 1: Field data of MDD, L.L., OMC and Fines (A-2 type soils) A - 2 Type MDD (kg/m 3 ) OMC (%) L.L. (%) Fines (%)

4 Table 2: Percent fines, measured and estimated compaction characteristics values S.No. Percent fines (%) Estimated MDD (kg/m 3 ) Actual MDD (kg/m 3 ) Estimated OMC (%) Actual OMC (%) MDD (kg/m ) OMC (%) 3 2 MDD= F F -70,606F A-2 Type Fines (%) Fig. 4: Plot of MDD Versus Fines (A-2 Types) OMC=0.0005F F F Fines (%) Fig. 5: Plot of OMC Versus Fines (A-2 Types) RESULTS AND DISCUSSION The particle distribution envelope indicates that these A-2 type soils are major sands with pockets of gravels not exceeding 6%. The clay percent ranges between 10 and 20%, silts are below 10%. The soils therefore can be Actual MDD (kg/m 3 ) Actual OMC (%) y = x R 2 = Estimated MDD (kg/m 3) Fig. 6: Plot of Actual MDD Against Estimated MDD Estimated OMC (%) Fig. 7: Plot of Actual OMC Against Extimated OMC classified as clayey sands. Since they are lacking in gravels but with appreciable percent of clays, they will require some form of stabilization for optimum utilization in road construction. 436

5 Figure 4 indicates a plot of MDD against fines percent. Increase in fines percent implies greater porosity and requires more water for the compaction of the soil. This therefore reduces density and consequently lowers the MDD values. A sharp drop in MDD values is noticed for fines percent between 14-25%, but remains almost constant between 26 and 36%. Between 14 and 25% the soil continues to require more water as a result of increasing porosity. However, after 25%, the soil probably achieves its maximum porosity and remains unaffected by increase in fines percent thereby maintaining almost constant MDD values. In Fig. 5, increase in fines percent results in increased water requirements due to greater specific surface of the soils. As fines percent increase there seems to be a significant increase in the optimum moisture content. Unlike Fig. 4, increase in fines percent progressively influences optimum moisture content more than maximum dry density. Figure 6 and 7 explain the correlation between fines, MDD and OMC. The high correlation coefficient of 92 and 93% for MDD and OMC respectively indicate that the estimated values are quite close to the actual laboratory values. This shows that for A-2 type lateritic soils, a simple particle size distribution test to obtain fines percent may be used to predict the compaction characteristics of these soils within the region. Compaction characteristics can then be predicted by the following equations. MDD = F F 2-70, 606F OMC = F F F where, MDD = Maximum dry density OMC = Optimum moisture content F = Fines percent CONCLUSION The compaction characteristics of lateritic soils from Western Niger Delta have been found to be dependent on the fines percent in the soil. Fines percent have been used to predict compaction characteristics with appreciable success. Different equations have been developed to relate fines percent to Maximum Dry Density (MDD) and Optimum Moisture Content (OMC). The validation of the models using the field data from the region yielded correct prediction of 92 and 93% for MDD and OMC, respectively. The models will aid road construction engineers to quickly estimate compaction characteristics without the laborious procedures of compaction test. ACKNOWLEDGMENT The Project Manager, Julius Berger Nigeria PLC and the entire geotechnical laboratory staff of the Railway project, Delta State Nigeria are highly acknowledged for their assistance during the laboratory analyses of the soil samples. REFERENCES Akpokodje, E.G., The engineering geological characteristic and classification of the major superficial soils of the Niger Delta. Eng. Geol., 32: Alabo, E.H., W.H. Fitzjohn and F.A. Ogare, Geotechnical properties of tropical red soil from part of eastern Niger Delta. J. Min. Geol., 21(1-2): Allen, J.R., Late quaternary Niger Delta and adjacent areas. sedimentary environment and lithofacies. Am. Assoc. Petrol. Geol. Bull., 49: Arumala, J.O. and E.G. Akpokodje, Soil properties and pavement performance in the Niger Delta. Q. J. Eng. Geol., 20: Johnson, A.W. and J.R. Shallberg, Factors that Influence Compaction of Soils. Bulletin No. 272, Highway Research Board, National Academy of Sciences, Washington, D.C. Kofiatis, G.P. and C.N. Manifopoulous, Correlation of maximum dry density and grain size. J. Geotech. Eng. Div-ASCE, 108(GT9): Omar, M., A. Shanableh, A. Basma and S. Barakat, Compaction characteristics of granular soils in United Arab Emirates. Geotech. Geol. Eng., 21: Rahn, P.H., Engineering Geology: An Environmental Approach. Prentice Hall. New Jersey US, pp: 275. Reijers, T.J.A., S.W. Petters and C.S. Nwajide, The Niger Delta. In: Reijers, T.J.A. (Ed.), Selected Chapters on Geology. Shell Petroleum Development Company, Warri, pp: Road Research Laboratory, Soil Mechanics for Road Engineers HMSO, London, pp: Short, K.C. and A.J. Stauble, Outline of the geology of Niger Delta. Am. Assoc. Petrol. Geol. Bull., 51: Ugbe, F.C., Engineering Geological Properties and Pavement Construction Qualities of Lateritic Soils from the Western Niger Delta. Unpublished Ph.D. Thesis, University of Port Harcourt, Nigeria. Weber, K.J. and E.M. Daukoru, Petroleum Geological Aspects of Niger Delta. Tokyo, 9th world Petroleum Congress Proceedings, 5(2): Winterkorn, H.F., Application of granulometric principles for optimisation of strength and permeability of granular drainage structures. Highway Res. Rec., 55(203):

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