Estimation Of Swelling Potential Of Enugu Shale Using Cost .

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Vol. 15(1), pp. 10-21, January-March, 2020DOI: 10.5897/IJPS2020.4865Article Number: 01F7D2C62950ISSN: 1992-1950Copyright 2020Author(s) retain the copyright of this tional Journal of PhysicalSciencesFull Length Research PaperEstimation of swelling potential of Enugu Shale usingcost effective methodsChidiebere Nnamani1* and Ogbonnaya Igwe21Department of Geology and Mining, Faculty of Applied Natural Science, Enugu State University of Science andTechnology, Enugu State, Nigeria.2Department of Geology Faculty of Physical Science, University of Nigeria, Nsukka, Enugu State, Nigeria.Received 4 January, 2020; Accepted 21 January, 2020The behavior of swelling soils is mainly governed by its mineralogical composition as well as itsenvironmental factors and stress history. Enugu Shale is one of these shales that assessment of its soilswelling potential cannot only be based on its mineralogical composition alone. The identification of itsclay mineral types is basic to understand the roles of other factors of swelling in the soils. The resultsof particle size distribution indicated that Enugu Shale is dominated by fine-grains with average meanof 69.65, 23.68 sands and 6.67% gravels. While the Atterberg’s limit values are moderate to high, withliquid limit ranging from 22-66%, plastic limit 0-39% and plasticity index 0-39%, abundance of majorelemental oxides show that SiO2 (50.4-88.1%), Al2O3 (6.29-28.23%) and Fe2O3 (0.98-12.25%) constituteover 90% of the bulk chemical compositions of the studied area. The studied area is dominated by A-7soils and low plasticity clay soils according to AASHTO and USCS classification system. The results offree swell ratio range from 1.02-1.45 which indicates that studied area is dominated by mixture ofswelling and non-swelling clay minerals. The Van der Merwe’s charts shows low to medium swellingpotential. These results show that the study area is dominated by low to medium swelling soils whichneed to be modified and upgraded before it can be used as subgrade material.Key words: Swelling potential, Enugu Shale, free swelling ratio, correlation and Van der Merwe’s chart.INTRODUCTIONThe studies of expansive soils have in recent timeattracted a great deal of attention from engineeringconstruction practitioners. For example, Enugu Shale insouthern Nigeria is mostly underlain by soft sedimentswhich are prone to expansion in the presence ofabundant precipitation in the wet season in addition toclay mineralogy of the soils and other environmentalfactors prevalent at a time in the history of the soils. Theswelling and shrinkage phenomenon associated with thesoils of this region can be detrimental to engineeringprojects such as pavement, foundation, slope stabilityetc. Shale exhibits a wide spectrum of geotechnicalcharacteristics especially as the moisture contentincreases and has often been a cause for concern onenvironmental geotechnical issues (Aghamelu et al,2011). Enugu Shale is one of these shales thatsignificantly show changes in volume on addition ofmoisture. Severally studies have identified thecharacteristics of the Shale (Okagbue and Aghamelu,2010; Ekeocha, 2015; Oyediran and Fadamoro, 2015;*Corresponding author. E-mail: agree that this article remain permanently open access under the terms of the Creative Commons AttributionLicense 4.0 International License

Nnamani and Igwe11(b)(a)Figure 1. Evidence of failure of engineering projects in the studied area.Figure 2. Geologic map of Anambra Basin showing Enugu Shale.Source: Nwajide and Reijers (1999).Tijani, 2012).The geology, climatic conditions, environmental factorsand drainage conditions provide a natural setting for theoccurrence of swelling/shrinkage phenomena. Structuraldamage caused by swelling phenomena is evident in thesoils of Enugu Shale in the Enugu metropolis (Figure 1).Evaluation of swelling characteristics of the soils usingempirical estimation will be of much help to thegeotechnical engineers for ease, quick and affordableunderstanding of the problematic soils of the metropolis.The method adopted in the work of Sridharan andPrakash (2000) was employed to characterize themineralogy characteristics of the soil using free swellingratio in comparison with the existing knowledge.GeologyEnugu Shale overlays the Agbani Sandstone/AwguShale. It is a lateral equivalent of Nkporo/Owelli formationand one of the oldest deposit of Anambra Basin (Nwajide,1990). Enugu Shale consists of fissile, grey shale withextra formational clast capped on top by Ironstone withpresence of pyrite.The shale is associated with extensive synsedimetarydeformation structures (Nwajide and Reigers, 1999) andlies in the eastern part of Anambra Basin (Figure 2).Enugu Shale is well exposed along Enugu-OnitshaExpress Way by New-Market flyover and along EnuguPort Harcourt Express Way by Ugwuaji flyover.

12Int. J. Phys. Sci.The highly weathered Enugu Shale consists of dirtybrown lateritic regolith that is porous and variessignificantly up to a maximum depth of 20 m, dependingon the topography and drainage conditions (Ekeocha,2015).mineralogy. The free swell ratio is calculated as follow:Climate, physiography and drainageRESULTS AND DISCUSSIONThe Enugu metropolis is bounded by latitudes 6 22’ Nand 6 30’ N; and longitudes 7 27’ E and 7 47 ’E; and lieswithin the rainforest belt of Nigeria. The two mainseasons that exist in Nigeria are the dry season that runsthrough the months of October to March, and the rainyseason that begins in the late March and ends in October(Nwankwor et al., 1988). The wet period is mostlycharacterized by moderate temperatures, and highrelative humidity, while the dry seasons have hightemperatures and lower relative humidity.The strike of the geomorphic feature in the Enugumetropolis runs through north-south trending escarpment.The scarp slope of the Enugu escarpment rises sharplyto the western side, and attains a maximum meanelevation of about 400 m above mean sea level. Thiselevation is continuous into the Udi Plateau.Enugu metropolis is drained by Ekulu, Iva, Ogbete andNyaba rivers which rises from near the base of theescarpment and flow towards the east into the CrossRiver Basin. The study area is well drained on thewestern side due to geomorphological feature of the areawhile it is poorly drained in the eastern side due togeomorphologic characteristics of the area.Particle size distribution analysisMATERIALS AND METHODSA total of thirty samples were collected from different places acrossEnugu metropolis (Table 1). The samples showed various degreeof weathering ranging from slightly weathered to moderatelyweathered. The samples were collected with the aid of 6 incheshand auger, with sampling depths ranging from 0.5 m to 3.5 m. Thesampling strictly followed standard procedure for soil sampling asspecified in British Standard Institution (BSI) 1377 (1990). Thesampling and laboratory testing were conducted between June andJuly 2017. The samples were taken to the laboratory for varioustests such as Atterberg’s limits (plastic and liquid limit), free swelltest and particle size analysis.Particle size analysis was conducted on the samples by ovendried at 105 C of 300 g of samples each. The oven-dried sampleswere sieved through the various set of BSI sieves, the sampleretained on each sieve was weighed and cumulative weight passingthrough each sieve was calculated as a percentage of the totalsample weight. Atterberg’s limits were done adopting the BSI 1377(1990) test 1A.Free Swelling Ratio (FSR)Sridharan and Prakash (2000) proposed the classification of claymineral type based on Free Swell Ratio (FSR) (Table 2). The freeswell ratio gives realistic information about soil expansivity and clayFSR Vd/Vk(1)Where Vd volume of soil in distilled water and Vk volume of soilin kerosene.Particle size distribution analysis showed the crushedsamples consist of 21.67-93.97% fines and 6-72.52%sands with average mean values of 69.65, 23.68 and6.67% for fines, sands and gravels respectively (Table 1).The particle size distribution curves are shown in Figure3. The dominance of fines over sands and gravels is anindication of a non-uniform distribution of grain sizeswhich imply poor grading.Atterberg’s limitsConsistency tests showed liquid limits, plastic limits andplasticity indices range from 22-66, 0-39 and 0-39%respectively. The soils plasticity range from low plasticityto high plasticity according to Bell (2007) with descriptiveclassification of lean to fat. Plasticity chart (Figure 4)shows the plasticity characteristics of the tested samplesin the studied area.Clay content and activityBased on the results of index properties using Skempton(1953) and as modified by Savage (2007), clay contentand activity were determined. Activity (A) values rangefrom 0-2.02 and clay content ranges from 0-52.63% wereobtained. With average means of 0.46 and 30.49% foractivity and clay content respectively. The activity of thesoils showed inactive to active with inactive dominatingthe soils of the studied area (Table 1).Free Swell Index (FSI) and Free Swell Ratio (FSR)Free Swell Index and Free Swell Ratio values asobtained by laboratory analysis and empirical evaluationshowed range of values from 8-45% and 1.08-1.45 forFSI and FSR respectively (Table 1). All the testedsamples have FSR above 1.0 ( 1.0 is regarded asnonswelling clay otherwise known as kaolinitic clay) butare within the range of 1.0-1.5 which are regarded asmixture of swelling and nonswelling clay and dominatedmostly by kaolinitic and montmorillonitic clay mineralsaccording to Prakash and Sridharan (2000) (Table 2).The results agree with reports of Ekeocha (2015),Oyediran and Fadamoro, (2015) and Tijani (2012) in thestudied area.

Nnamani and IgweTable 1. Physical properties of samples from the studied 11B12131415161718192021222324252627MeanStd. 11231120.511114110.5Particle size 1.20621.6754.9772.5293.97Atterberg’s Limits 939Clay content (%)FSI (19)13

14Int. J. Phys. Sci.Table 2. Classification of soils based on FSR.FSR 1.01.0 – 1.51.5 – 2.02.0 – 4.04.0Clay typeNon-SwellingMixture of Swelling and Non SwellingSwellingSwellingSwellingSoil expansivityNegligibleLowModerateHighVery HighDominant clay mineral typeKaoliniticMixture of Kaolinitic and ntmorilloniticSource: Sridharan and Prakash (2000).Correlations of physical parametersThe correlation is significant at P 0.05 (Table 3).Correlation between activity of the soils and otherphysical parameters is significant only forplasticity index and liquid limit. Activity of soils ispositively correlated with plasticity index and liquidlimit; also, strongest correlation was obtainedbetween activity and plasticity index (r 0.827)while between activity of soils and liquid limit is amoderate correlation (r 0.463).Correlation between plasticity index and otherparameters is significant for soil activity, liquid limitand fines. The correlation between plasticity indexand fines is a moderate positive correlation at r 0.43.Correlation between FSI and other parametersis significant only for FSR and liquid limit. BothFSR and liquid limit are positively correlated withFSI. The correlation between FSI and FSR is verystrong at r 0.998 while that of FSI and liquid limitis moderate at r 0.429. Again, the correlationbetween FSR and liquid limit is moderatelypositive at r 0.415.Correlation between the liquid limit and otherparameters is significant for activity of the soils,plasticity index, FSI, FSR, plastic limit and clayfraction. All the significant parameters havepositive correlation with liquid limit. The correlationbetween liquid limit and; plasticity index is verystrong at r 0.858, plastic limit is strong at r 0.705 and clay fraction is very strong at r 0.755.The correlation between plastic limit and otherparameters is significant only for liquid limit andclay fraction. Correlation between plastic limit andclay fraction is very strong at r 0.960.Lastly, the correlation between percentage finesand other parameters can only be significant forpercentage sands. This correlation is negativelyvery strong at r -0.892.Activity, plasticity index, FSI, FSR, plastic limitand clay fraction were correlated with liquid limit atsignificant level of 0.05 excellently. The correlationcoefficients have considerable impact onpredicting the swelling characteristics of the soilswhen related with report of Bell (2007).Soil classificationTable 1 shows the classification of soils of thestudied area using USCS and AASHTOclassification systems. Figure 5a and b showdistribution by percentage of soils by AASHTOand USCS classification system. Figure 5a showsthe dominance of A-7-6 soils in the studied areawith 36.67% of the entire samples population. Theresults also show that the studied area is mostlydominated by A-7 soils in the eastern part and thishas contributed immensely to the state of roads inthe area (Figure 1). Figure 5b shows that thestudied samples are dominated by low plasticityclay, high plasticity silt and high plasticity clay withpercentage distribution of 40, 26.67 and 16.67%respectively. The results also indicate that thestudied area is characterized by swelling soils andcaution should be applied before embarking onengineering construction in the studied area.Swelling potentialEvaluation of swelling potential of studied soilsamples were carried out based on the results ofAtterberg’s limit, free swell test and empiricalestimation. The work of Van der Merwe (1964)was applied to investigate the swelling potential ofthe studied soils. Figure 6 shows the k linessuperimposed on the Van der Merwe swellingchart to determine the swelling potential of thestudied soil samples in the studied area. The charthas a defined range of low – medium – high –very high zones for swelling potential. The Vander chart is a plot of gross clay fraction (P002)versus gross plasticity index (Pg). There is amathematical derivation of line representingswelling potential by a factor k, which defined the

Nnamani and 0STN8STN9STN10A60Percentage STN26STN27STN2500.0010.010.1Particle size in mmFigure 3. Particle size distribution curves of the soil samples.110

Int. J. Phys. Sci.PI16454035302520151050CHCLCL-ML010MH or OHML or OL2030405060LLFigure 4. Plasticity chart of the studied soil samples.(a)(b)Figure 5. Pie chart showing soil classification of the samples by AASHTO and USCS classification system.Figure 6. Swelling potential based on Van der Merwe’s chart on the tested samples.70

Nnamani and IgweTable 3. Correlation between some physical parametersParameterActivity of soilPlasticity indexFree SwellingFSRLLPL% FineClay fraction% 80.71225Activity of soil29Plasticity IndexFree SwellingFree Swelling RatioLiquid limitPlastic limit%FineClay 8920.00025-0.0780.71225*Correlation is significant at the 0.05 level (2-tailed).12617

18Int. J. Phys. Sci.Table 4. Elemental oxides of the tested lling zones approximately.(P002 – 0.73k) (Pg – 0.16 P002 k0.4) – k 0(3)The swelling potential is defined by k as follows;K 16 Low swelling potential16 k 27 Medium swelling potential27 k 37 High swelling potential37 k Very high swelling potentialPg (Gross plasticity index) 18.99R – 19.47 (Abbas,2016)(4)P002: Gross Clay Fraction.The studied samples were dominated by low tomedium swelling soils.Free swelling test results were used to calculate freeswelling ratio. Subsequently, the free swelling ratio (FSR)results were also used to identify the clay mineralspresent in the study area (Table 1) in comparison to theclassification by Sridharan and Prakash (2000) (Table 2).The results of XRD showed that the studied samplesconsist of kaolinite, Hametite and quartz (Figures 7 and8). The results obtained agree with work of Oyediran andFadamoro, (2015) and Ekeocha (2015) on claymineralogy of the studied area.Soils elemental oxidesThe chemical characteristics of shale are mainly of chemistry of the main minerals, cementingmaterials as well as cation exchange capacity of the clayminerals. Table 4 shows the elemental oxides of thesamples in the studied area. Figure 9 shows therelations

Free Swell Index (FSI) and Free Swell Ratio (FSR) Free Swell Index and Free Swell Ratio values as obtained by laboratory analysis and empirical evaluation showed range of values from 8-45% and 1.08-1.45 for FSI and FSR respectively (Table 1). All the tested samples have FSR above 1.0 ( 1.0 is regarded as

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