University of Maiduguri Faculty of Engineering Seminar Series Volume 7, July 2016 An Investigation of Geotechnical Properties of Bama Ridge Soil as a Suitable A.M. Kundiri, A.S. Muhammed and I.S. Muhammad Department of Civil and Water Resources Engineering, University of Maiduguri, Borno State, Nigeria alikundiri@yahoo.com; +2348034633633 Abstract Roads construction over loose soil deposit could pose a serious problem for an effective motor ability due to low bearing capacity and non-plastic nature of the soil. It is therefore, pertinent to investigate the geotechnical parameters of the Bama Ridge soil with a view to ascertain its suitability as a sub grade material for road construction. Five different soil samples were collected from five different locations at an interval of 250m and at average depth of 0.5 1m using the method of disturbed sampling. The soil was then preserved in plastic bags to avoid loss of moisture and then transported to the laboratory for subsequent tests. The index properties of the soil revealed that they were dominantly non-plastic sand classified as A 3 (fine sand) and CL (in organic silty clay) based on the Association of American States Highway and Transportation Officials (AASHTO) and Unified Soil Classification System (USCS). Results from the compaction characteristics indicate an increase in Maximum Dry Density (MDD) and decrease in Optimum Moisture Content (OMC) with higher compaction effort. Key words: Bama Ridge soil, geotechnical, sub grade, index properties, Maximum Dry Density, Optimum Moisture Content 1.0 Introduction Paved and feeder roads construction over loose soil deposit could pose a serious problem for an effective motor ability due to low bearing capacity and non-plastic nature of the soil. Some parts of Borno and Yobe States are covered with such types of soil. Borno State is characterized by heterogeneous soil types that ranges from the expansive lacustrine deposit of black cotton soil and sandstone deposits sporadically found in the northern part, laterite and jiglin (a local name for some special hardened pebbles) in the southern part and some parts of Maiduguri and its environs (Kundiri et al., 2007). However, Around Maiduguri and Bama towns, there exist several deposits of light brown to yellowish brown ferruginous sand- stones essentially Arkosic Arenite with gradations to feldspathic grey wacke popularly known as Bama ridge soil (Carter et al., 1963; Zarma, 2000). Bama ridge soil probably a barrier beach is about 10 15m high and it is approximately 500m 1000m wide and about 350m long. The sand ridges trends NW SW for about 160km running from Limani, a village near Nigerian-Cameroun frontier and extending towards the tip of the Mandara mountain in Nigeria. This sand ridge passes through Bama, Maiduguri and Magumeri up to Nguru and Gashua then finally flattens out beneath the sand dune of Niger plains (Pias and Guichard, 1957; Thiemeyer, 1992; Zarma, 2000; Kundiri et al., 2011; Hassan et al., 2012). It is therefore, pertinent to investigate the geotechnical parameters of such soils with a view to suitability as a sub grade material for pavement construction. Seminar Series Volume 7, 2016 Page 31
2.0 Methodology Soil samples were obtained from five different locations designated as S1 S5 along the ridge soil in Maiduguri (latitude 11 0 51 N and longitude 13 0 05 E). The samples were collected at an interval of 250m and at average depth of 0.5 1m using the method of disturbed sampling. The soil was then preserved in plastic bags to avoid loss of moisture and then transported to the Soil Mechanics Laboratory of Department of Civil and Water Resources Engineering, University of Maiduguri for subsequent tests. The soil specimens were prepared using water contents from 3 to 18% at increment of 3%, with three compactive efforts, namely: British Standard Light (BSL), British Standard Heavy (BSH) and West African Standard (WAS) compactive efforts. The tests were conducted based on procedures in BS 1377 (1990). The BSL compaction test was carried out using 2.5 kg rammer falling 30.48cm onto three layers, each layer receiving 27 blows, while BSH and West African Standard compaction tests were also carried out using a BS compaction mould with a 4.5 kg rammer falling 45.74cm onto five layers, each layer receiving 27 and 10 blows respectively (Ola, 1980; Osinubi, 1998). 3.0 Results and Discussion Index properties: The preliminary tests carried out on the five soil samples entail, Atterberg limits, grading characteristics and some physico- chemical properties such as ph and specific gravity; vital for soil classification is presented in Table 1. Table 1: Index Properties of soils used in the present study. Sample No. Atterberg Limits Grading Characteristics Seminar Series, Volume 7, 2016 Page 32 Physico Classification chemical properties ph AASHTO USCS Liquid Limit Plastic Limit Plasticity Index Grave l Sand Fine Specific gravity S1 10.2 - - 0 99.82 0.18 2.52 6.41 A 3 CL S2 12.2 - - 0.04 99.76 0.2 2.54 6.23 A 3 CL S3 13.5 - - 0 99.3 0.7 2.54 6.11 A 3 CL S4 15 - - 0 99.88 0.12 2.58 5.77 A 3 CL S5 11.8 - - 0 99.72 0.28 2.55 6.35 A 3 CL The physico- chemical properties of the Bama ridge soil showed that the degree of acidity or alkalinity of the soil measure based on the ph value ranged from 5.77 to 6.41. This indicated that the entire soil samples are slightly acidic in nature. In the vein, low values of specific gravity ranging from 2.52 to 2.58, suggested the presence of organic matter in the soil. The plasticity characteristics show that the soil samples are non plastic with a liquid limit of 10.2 15%. The soil samples were classified as A 3 (fine sand) and CL (in organic silty clay) according to AASHTO and USCS methods of classification respectively (AASTHO, 1986; Das, 2006). 3.1 Particle Size Distribution The particle size distribution presented in Fig. 1 shows that the soil consists of 0 0.04% gravel, 99.3 99.88% sand and 0.18 0.7% fine. The dominance of sand over gravel and fine indicated its non uniform in distribution of the grain size.
Percentage passing (%) Kundiri et al: An Investigation of Geotechnical Properties of Bama Ridge Soil as a Suitable S1 S2 S3 S4 S5 Particle Size (mm) Fig. 1: Particle Size Distribution of the soil samples 3.2 Compaction Characteristics The compaction characteristics which portrayed the moisture-density relationship of the soils are presented in Table 2. Table 2: Compaction Characteristics of soil used in the present study SAMPLE BSL BSH WAS MDD OMC MDD OMC MDD OMC S1 1.82 10.8 1.93 10.4 1.77 11.4 S2 1.78 10.4 1.88 10.6 1.72 12.8 S3 1.78 11.2 1.86 10.8 1.72 11.6 S4 1.79 11.8 1.84 10.8 1.73 12.2 S5 1.79 10.4 1.86 9.8 1.70 11.7 The Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) of the soils were observed to be within the range of 1.7 1.93Mg/m 3 and 9.8 12.8% respectively for all compactive efforts. The compactive behaviour of the Bama ridge soil is depicted in figures 2 to 4 for the five different samples. Sample S1 Sample S2 Fig. 2: Compaction curves for Samples S1 and S2 using varying compactive efforts Seminar Series, Volume 7, 2016 Page 33
Sample S3 Sample S4 Fig. 3: Compaction curves for Samples S3 and S4 using varying compactive efforts Sample S5 Fig. 4: Compaction curves for Sample S5 using varying compactive efforts The trends of the MDD and OMC for all the three compactive efforts showed that higher compaction energy resulted in higher dry densities, while the OMC decreases as the compactive effort varies from BSL, WAS and BSH. It could be inferred that higher MDD values could be due to increased penetration of the compaction rammer on soil surface, resulting in closer alignment of particles along the surface, yielding greater density. This is in agreement with findings presented in other studies (Daniel and Wu, 1993). The zero air void line (ZAVL) was drawn based on their respective specific gravity values using eq.1. Gs zav 1 1 wgs Where Gs = specific gravity and W = Moisture content 4.0 Conclusion Bama ridge soil which composed of deposits of light brown to yellowish brown ferruginous sand- stones, with the dominance of sand (99.3 to 99.88%) over gravel (0 to 0.04%) and fine (0.18 to 0.7%). This indicated that the soil is not uniformly graded and classified as A 3 (fine sand) and CL (in organic silty clay). The trends and values of the MDD and OMC for all the three compactive efforts revealed that higher compaction Seminar Series, Volume 7, 2016 Page 34
energy resulted in higher dry densities, with corresponding decreases in the OMC as the compactive effort varies from BSL, WAS and BSH. It could be inferred that higher MDD values could be due to increased penetration of the compaction rammer on soil surface, resulting in closer alignment of particles along the surface, thus yielding greater density. In view of the fore mentioned characteristics of this soil, it cannot effectively serve as a suitable earth fill material in pavement construction without improving the quality of the soil owing to its low bearing capacity and non-plastic nature. References AASHTO (1986). Standard Specification for Transportation Materials and Methods of Sampling and Testing 14 th ed. American Assoc. of States Highway and Transportation officials. BS1377 (1990). British Standard Methods of Test for Soils for Civil Engineering Purposes, British Standards Institution, London. Carter, J. D.; Barber, W. and Tait, E. A. (1963). The geology of parts of Adamawa, Bauchi and Bornu provinces in north east Nigeria. Geol. Surv. Nigeria, Bulletin No. 30. Das, B. M. (2006). Principles of Geotechnical Engineering, 6 th ed., Thompson, Canada, 686pp. Daniel, D. E., and Wu, Y. K. (1993). Compacted clay liners and covers for arid sites. Journal of Geotechnical Engineering, 119(2), 223 237. Hassan, M.; Uba, M. M. and Zarma, A. A. (2012). Hydro geophysical Investigation of River Aquifer interaction: A case study of Bama ridge shallow aquifer and river Ngadda, Dalori, North eastern Nigeria. Arid zone Journal of Engineering, Technology and Environment, 9, 115 123. Kundiri, A. M. and Mustapha A. (2007). Cement Stabilization of Bama ridge Soil, Nigerian Journal of Soil and Environmental Research, Department of Soil Science, Ahmadu Bello University, Zaria, Vol. 7: 102-108. Kundiri, A. M., S. Y. Umar and G. N. Bah (2011). Suitability of Bama ridge soil as road material, Nigerian Journal of Tropical Engineering, School of Engineering and Engineering Technology, Abubakar Tafawa Balewa University, Bauchi, Vol. 7 No.1: 14-20. Ola, S. A. (1983). Geotechnical behaviour of some Nigerian lateritic soils. In: Tropical soils of Nigeria in Engineering practice, A. A. Balkema, Rotterdam, pp.61-84. Osinubi, K. J. (1998). Influence of compactive efforts and compaction delay on lime - treated soil. Journal of Transportation Engineering. ASCE, 124(2), 149 155. Pias, J. and Guichard, E. (1957). Origines et consequences de l existence d un cordon sableux dans la partie sud-ouest de la cuvette tchadienne, C. R. Acad. Sci. 224: 791-793. Thiemeyer, H. (1992). A new c Record from the Bama ridge near Konduga, Borno State. Annals of Borno, University of Maiduguri press (8 & 9), 239 242. Zarma, A. A. (2000). Petrographic study of the sandstones exposed on the Bama ridge, Maiduguri. Borno Journal of Geology. 2(2), 65 77. Seminar Series, Volume 7, 2016 Page 35