PREDICTION OF ENGINEERING PROPERTIES OF TROPICAL SOILS USING INTRINSIC PEDOLOGICAL PARAMETERS

Quick and reliable information about the engineering properties of soi ls is needed for evaluating soils for nonagricultural uses,The objecti ves of this preliminary study were, (i) to relate some engineering pro perties of typical tropical soils from Nigeria to their mineralogy, (i i) to develop simple models for predicting and characterizing these en gineering properties from easily determinable soil properties, and (ii i) to compare values of the swell potential of these soils estimated b y various equations used in soil mechanics with values measured direct ly in the laboratory, Data from 30 soil samples collected across Niger ia were used for this study,The extent of the volumetric shrinkage (VS ) hazard posed by the soils is influenced more by the dominant clay mi nerals than by the texture or soil order, Generally, soils containing only kaolinite (1:1 mineral) had low VS values (<10%),whereas those co ntaining either low or trace concentrations of smectite or vermiculite (2:1 minerals) acted like expansive soils (VS 10-30%) in spite of the dominance of the 1:1 mineral, Soils with substantial amounts of eithe r smectite or vermiculite had very high VS values (>30%). There were s trong linear relationships between VS, liquid limit (LL), and plastic limit (PL) on one hand and cation exchange capacity (CEC), organic mat ter (OM), and clay content on the other. Regression equations develope d with CEC could not predict accurately the VS and LL of two of the 10 validation soils with <5 cmol(c)/kg CEC and dominated by kaolinite. T he OM-based model could not provide good estimates of the PL of the tw o vertisols with >80% VS values. The relationships between the soil pr operties and plasticity index were weak, Some nonlinear equations used to predict the swell potential of soils grossly underestimated the me asured shrink-swell hazard posed by these soils. These predictive empi rical equations need to be tested on a wider range of tropical soils t han were used in this study before any valid conclusions on their appl icability can be made.