Abstract—A clay soil classified as A-7-6 and CH soil according to AASHTO and unified soil classification system respectively, was stabilized using A-3 soil (AASHTO soil classification system). The clay soil was replaced with 0%, 10%, 20%, to 100% A-3 soil, compacted at both British Standard Light (BSL) and British Standard Heavy (BSH) compaction energy levels and using Unconfined Compressive Strength (UCS) as evaluation criteria. The Maximum Dry Density (MDD) of the treated soils at both the BSL and BSH compaction energy levels showed increase from 0% to 40% A-3 soil replacement after which the values reduced to 100% replacement. The trend of the Optimum Moisture Content (OMC) with varied A-3 soil replacement was similar to that of MDD but in a reversed order. The OMC reduced from 0% to 40% A-3 soil replacement after which the values increased to 100% replacement. This trend was attributed to the observed reduction in void ratio from 0% to 40% replacement after which the void ratio increased to 100% replacement. The maximum UCS for the soil at varied A-3 soil replacement increased from 272 and 770 kN/m 2 for BSL and BSH compaction energy level at 0% replacement to 295 and 795 kN/m 2 for BSL and BSH compaction energy level respectively at 10% replacement after which the values reduced to 22 and 60 kN/m 2 for BSL and BSH compaction energy level respectively at 70% replacement. Beyond 70% replacement, the mixtures could not be moulded for UCS test. Keywords—A-3 soil, clay soil, pozzolanic action, stabilization. I. INTRODUCTION LAY soils exist in different parts of the world and can cause serious damage to civil engineering infrastructures ranging from building structures to road structures [1]. The common clay minerals available are kaolinite, illite and montmorilonite. These clay soils in its in-situ form can exist as expansive clays or soft clays. These two processes are caused by the non availability or availability of water to the in-situ clay soil deposit. Expansive clay soils are common in semi- arid regions where availability of ground water is minimal and conditions are suitable for the formation of clay minerals such as montmorilonite [2]-[4]). Soft clay soil deposits are common in rain forest areas where ground water is always available to the clay soil deposit. Clay is a material with low strength and markedly affected by water but it can be relatively strong in dry condition [5]. If water is added to clay, it will behave as plastic or flow like liquid. Soft clay normally has very high percentage of clay fraction. Because of its low permeability, dissipation of excess pore pressure is slow. A-3 soils subgroup in American Association of State Highway and Transportation Officers (AASHTO) [6] soil classification system is placed in a lone column without M. M. Alhaji is with the Civil Engineering Department, Federal University of Technology, Minna, Niger State, Nigeria (08036133082; e-mail: a.mustapha@futminna.edu.ng). S. Sadiku is with the Civil Engineering Department, Federal University of Technology, Minna, Niger State, Nigeria (e.mail:sadikovurevu@yahoo.com). subdivisions like A-1 and A-2. A-3 soils are uniformly fine and non plastic sand which make its use in any component of road structure to be very minimal and almost completely neglected in AASHTO [6] soil classification scheme. It is therefore pertinent to put this class of soil into any possible engineering use. Soil stabilization is a technique introduced many years ago with the main purpose to render the soils capable of meeting the requirements of the specific engineering projects [7]. The commonly used stabilizers include ordinary Portland cement (OPC) and lime, with their stabilization mechanisms being relatively well understood [8]-[10]. Cong et al. [11] studied cement stabilization of clay soils with the mixture of sodium silicate and composite promoter. The authors realized that the supplementary cementing materials performed effective pozzolanic actions and improved the mechanical properties of cement stabilized clay soils. These soil stabilizing chemicals are either expensive or difficult to source in large quantity, hence the need to use sharp sand as alternative. Muazu [12] studied the stabilization of fine lateritic soils using river sand. The sand was mixed at 0%, 2%, to 8% by weight of the dried lateritic soil. The Maximum Dry Densities were found to increase continuously from 1.920 at 0% sand content to 1.980g/cm 3 at 8% sand content. The Optimum Moisture Content (OMC) decreased from 29% at 0% sand content to 25% at 8% sand content. The author did not consider the compaction characteristics beyond 8% sand content. Joel and Agbede [13] studied the effect of lime on sand stabilization of Igumale shale. The authors replaced the shale with 0%, 10%, 20% to 50% sand by weight of the Igumale shale. The mixture was further admixed with 0%, 2%, 4% to 14% lime by weight of the Igumale shale. The result showed that, at 0% lime, the MDD of Igumale shale increased from 1.51 g/cm 3 at 0% sand to 1.69 g/cm 3 at 50% sand content. Similarly, at 0% lime, the UCS increased from 360 kN/m 2 at 0% sand to maximum of 440 kN/m 2 at 20% sand content after which the value decreased to 178 kN/m 2 at 50% sand content. The author did not consider the geotechnical properties beyond 50% sand content. This work is therefore aimed at replacing A-3 soil (obtained from river sand) with clay soil from 0% to 100% in order to stabilize the clay soil. II. MATERIALS AND METHODOLOGY A. Material The materials used for this study include clay soil collected from Niger State Polytechnic, Zungeru, Niger State. The clay soil was collected at a depth of between 1.0 to 1.5m. The disturbed clay soil was prepared according to the method highlighted in part 1 of B. S. 1377 [14]. Stabilization of Clay Soil Using A-3 Soil Mohammed Mustapha Alhaji, Salawu Sadiku C World Academy of Science, Engineering and Technology International Journal of Geological and Environmental Engineering Vol:9, No:10, 2015 1272 International Scholarly and Scientific Research & Innovation 9(10) 2015 scholar.waset.org/1307-6892/10002813 International Science Index, Geological and Environmental Engineering Vol:9, No:10, 2015 waset.org/Publication/10002813