Evaluation of plasticity and consolidation characteristics of migmatite–gneiss-derived laterite soils

Abstract

Information on plasticity and consolidation characteristics of soil materials have been found to be profoundly important for preliminary structural planning and designs since these properties influence soils’ compressibility and settlement characteristics and, by extension, the performance of any engineering structure on the soils. The dependency or relationship of consolidation characteristics with plasticity characteristics of remolded migmatite–gneiss-derived laterite soils from southwestern Nigeria was statistically evaluated. A total of eight (8) bulk disturbed soil samples were subjected to Atterberg limits tests and one-dimensional consolidation tests following British Standard BS 1377 methods. Further, the results obtained were subjected to regression analysis. The plasticity index (PI), linear shrinkage, and shrinkage index values ranged from 8.0 to 33.65, 4.3 to 10.7, and 19.0 to 50.2, respectively. The average coefficient of consolidation (Cv) and compression index (Cc) values ranged from 0.02184 to 0.03290 mm2/min and 0.0203 to 0.0812, respectively. The correlation coefficient of compression index values with plasticity index and shrinkage index values is 0.90 and 0.72, respectively. The coefficient of correlation (r) of the relationship between consolidation coefficient values and consolidation pressure (AP) values of 20–160 kPa (loading session only) is 0.97. The coefficients of correlation (r) of average consolidation coefficient values with linear shrinkage, shrinkage index, and plasticity index values are 0.60, 0.73, and 0.88, respectively. Hence, coefficient of consolidation and compression index have better correlations with plasticity index over shrinkage index and linear shrinkage. Further, the correlation coefficient of plasticity Index (PI) with all the consolidation coefficient values, derived at each stage of effective vertical consolidation pressures (AP) of 20–160 kPa (loading and unloading), is 0.79. Based on these results, correlation equations for predicting consolidation coefficient and compression index were proposed. This evaluation has aided better understanding of the relationship between consolidation and plasticity characteristics of migmatite–gneiss-derived laterite soils and can be applied to several other basement terrains.