Prediction of maximum dry unit weight and optimum moisture content for coarse-grained lateritic soils

The continual depletion of valuable earth resources due to structural developments have been of much concern in the quest for sustainability, thus, the importance of soil compaction cannot be overemphasized. The world population is increasing every day and there is constant need of more infrastructures such as roads, runways, dams, buildings, jetties, railways etc. All these structures are built on soils which sometimes do not have adequate bearing capacity to resist the loads coming on them. In Nigeria, the common soils used for construction work which are laterite are sometimes found unsuitable in its natural state for intended use. Thus, there is the need for soil improvement of which compaction is among the commonest and the cheapest. Laterites are described as highly weathered and altered residual soils formed by insitu weathering and decomposition of parent rocks under tropical and subtropical climatic conditions (Aginam et al., 2014). The increasing use of this soil is linked to its availability, cheapness and amenability to compaction. Compaction of lateritic soils like other soils, increases the bearing capacity of the soils. It also decreases the amount of undesirable settlement of structures constructed over such soils and increases the stability of slopes of embankments (Ratnam & Prasad, 2019). The strength of foundations largely depend on compaction control which is based on finding the maximum dry unit weight (MDUW) corresponding to an optimum moisture content (OMC) at a given compaction energy. Laboratory compaction is usually done in Nigeria with British Standard Light (BSL) (equivalent of standard Proctor method), West African Standard (WAS), and British Standard Heavy (BSH) (equivalent of modified Proctor method). These methods are laborious, time-consuming and material-consuming (Jayan & Sankar, 2015). The shortcomings outlined above together with proof by some earlier authors Ring et al. (1962), Ramiah et al. (1970), Benson et al. (1998) and most recently Anjita et al. (2017) that soil type, its grain size distribution, index properties, and specific gravity influence the MDUW and OMC of soils led researchers to develop empirical relationships between MDUW/OMC and index properties of soils. Such index properties as liquid limit (LL), plastic limit (PL), plasticity index (PI), fines content (FC), sand content (SdC) etc. have previously been used. Abstract Laboratory compaction of soils is an important aspect in the selection of materials for earthwork construction. Owing to time constraints and concern for depleting resources, it becomes imperative that empirical relationships would be developed to predict compaction parameters, maximum dry unit weight (MDUW) and optimum moisture content (OMC) from easily measured index properties. The aim of this note is to develop empirical relationships between MDUW /OMC and logarithm of compaction energy (E)/fines content: sand content ratio (FC/SdC) for some lateritic soils. Index property tests were carried out on twenty (20) lateritic soils to classify them and obtain the FC/SdC. The soils were compacted at three compaction energies; British Standard Light (BSL), West African Standard (WAS) and British Standard Heavy (BSH). Two models were developed from relationships based on slopes and intercepts derived from MDUW/OMC versus log E plots; one model employs ‘FC/SdC’ and one compactive effort (BSL) while the other model employs only ‘FC/SdC’. The models were validated for robustness with soils used in the development of the models and six (6) other soils not used to develop the models. For the prediction of BSH, the model employing FC/SdC and one compactive effort showed typical errors of ±0.63 kN/m3 and ±0.76% for MDUW and OMC respectively. The model employing only FC/SdC showed typical errors of ±0.4 kN/m3 and ±0.83% for MDUW and OMC respectively. The typical errors are within allowed variations for projects and standards for MDUW and OMC, thus the models are quite robust.