Equivalent Blows Approach to the Calibration of a Minicompactor for Laboratory Use

Abstract

Researchers and laboratory personnel often encounter some difficulties when using standard compaction methods to compact a soil sample before they are tested with the triaxial machine. The difficulties include; difficulties in extrusion, bulkiness of rammers, and non-uniformity in the distribution of blows, and associated sample disturbance when preparing specimens for triaxial testing. These problems have been curbed by the use of minicompactors which are newer technologies. A minicompactor (Nanjing Soil Minicompactor) manufactured to enable production of 39.1mm diameter that can fit into triaxial machine (Model TS2-1) was used for the compaction studies. The minicompactor is made of a split mold of 96.06cm³ by volume. The rammer weight 600g fits well to the internal circumference of the mould. The drop height is 30cm, which is relatively short. These features are very desirable to contemporary researchers, but it will be very important to ensure uniformity with the standard compactors on which the experimental methodologies were originally based. Ignoring this will lead to an erroneous assumption that the minicompactors would achieve the same compaction as the standard ones using the same specifications, but this would result a level of inconsistency that would affect the results of the experiments. To bridge this gap, this study, attempts to determine the number of blows with the Nanjing minicompactor that will achieve the same MDD and OMC with those conventional standards: - British Standard Light (BSL), Reduced British Standard Light (RBSL), West African Standard (WAS), and British Standard Heavy (BSH), using the same lateritic soil material and same number of layers. The research shows that there is a consistent increase in Maximum Dry Density and decrease in Optimum Moisture Content as compactive efforts increased. A total of 11 compactions were made using the minicompactor; seven were made at 3 layers using 4,8,12,16,20,24, and 28 blows while four were made at 5 layers using 34, 38, 42, and 46 blows.  Plots of the Maximum Dry Densities against Number of Blows were made for the 3 layers as well as the 5 layers. Using statistical models, the number of blows that are equivalent to the known standards were established. It was recommended that for the Reduced British Standard (Light), 22 blows at 3 layers; for the British Standard (Light), 27 blows at 3 layers; for the West African Standard, 42 blows at 5 layers; and for the British Standard (Heavy), 46 blows at 5 layers would be used to achieve a corresponding MDD and OMC.

Keywords; compactors, calibration, lateritic, blows, dry density, moisture content.