MULTI-CYCLIC INFLUENCE ON STANDARD LABORATORY COMPACTION OF RESIDUAL SOILS

Standard laboratory compaction tests (e.g., BS, AASHTO, WA) originally designed to simulate and control compaction in field earthworks have fallen short of achieving their stated objective. Several reasons have been advanced to explain this, but the most important, which is advan ced here, is the multiple recycling or multi-cyclic compaction of soil samples (at least five times per test) involved in almost all these s tandard tests. This recycling has been observed from a previous study to fall within the zone of influence of multi-cyclic compaction. This paper, therefore, investigates the influence of multi-cyclic compactio n on the maximum dry density (MDD) and optimum moisture content (OMC) of some deltaic lateritic soils (derived from deltaic sedimentary depo sits) that are currently being used for the construction of many road embankments in the Port Harcourt area of eastern Nigeria. Samples of t hese soils were subjected to standard Proctor and break-up Proctor (si milar procedure to standard Proctor but with a fresh batch of soil use d for each point on the density-moisture curves) compaction tests. The standard tests were observed to underestimate the MDD values, albeit with a decreasing influence as the depth of sampling/extraction increa sed. This effect was minimised at a depth of around 5.0 m. In addition , differences in dry densities obtained from both methods were observe d to maintain, fairly well, fourth-order polynomial relationships with the corresponding moisture contents through computer-aided statistica l analysis. Also, this relationship was employed to present a model - in the form of a family of curves - from which the more reliable break -up densities could be predicted from the less tedious, and hence more popular, standard tests.