The falling weight deflectometer (FWD) is used worldwide as an established, valuable, nondestructive road testing device for pavement structural analyses. The FWD is used mostly for rehabilitation project level design investigations and for pavement management system (PMS) monitoring on a network basis. In project level investigations, design charts based on both empirical relations and mechanistic or theoretically based approaches are often used to provide structural evaluations and rehabilitation options. The full mechanistic approach normally uses multi-layer linear elastic theory and back-calculation procedures that have come under scrutiny owing to the inaccuracy of results. A semi-mechanistic, semi-empirical analysis technique has been developed in South Africa in terms of which deflection bowl parameters, measured with the FWD, are used in a relative benchmarking methodology in conjunction with standardised visual survey methodology to give guidance on individual layer strengths and pinpoint rehabilitation needs. This benchmark methodology enables the determination of the relative structural condition of the pavement over length and in depth without the requirement for detailed as-built data. A further correlation study with calculated surface moduli and deflection bowl parameters is presented here for granular base pavements, which can enhance benchmarking methodology.
Deltaic laterite is the most suitable and most widely used soil material for road embankment in the Niger Delta. Usually, its natural characteristics fall short of the minimum requirements for such applications hence it has to be stabilised to improve its properties. In this study, samples of deltaic lateritic soils were subjected to mechanical (with or without controlled sand addition), cement and cement-sand (composite) stabilisation methods to improve strength for improved engineering applications. Mechanical stabilisation was found to satisfy subgrade requirements while the addition of sand produced sub-base material quality at best depending on compacted maximum dry density (MDD), which itself is dependent on the optimum sand content (OSC). The OSC was also shown to affect the optimum moisture content (OMC) and the soaked California bearing ratio (CBR) of stabilised specimens. Combination of the test results produced a graphical model to predict the influence of mechanical stabilisation on the soil materials using the percentage fines (that is, passing through a 75 mm sieve) obtainable from wet sieving. Cement stabilisation of the soil (by indigenous highway standard) produced base-course quality materials with cement content in excess of 12 %, which is economically unviable. However, the addition of controlled proportions of sharp sand (also abundant in the Niger Delta) to the soilcement mixtures produced base-course quality materials with 6 % cement (less than half of that obtained through only cement stabilisation) and about 40 % sand content. A model was also presented to predict the other constituents of sand-cement stabilisation using the percentage fines obtainable from wet sieving.