ABSTRACT

This work entailed investigating the effect of mechanical and chemical improvement of deltaic lateritic soils and testing an approach that could improve the bearing capacity of the lateritic soils found in Southern Delta area, precisely the eastern Warri Zone.

Mechanical stabilization was carried out by adding river sand to the laterite in various proportions, while chemical stabilization was carried out using cement, sand and a mixture of cement and a plasticizer. Various tests were conducted on the laterite before and after stabilization, to study the effect the various stabilization techniques on the properties of the laterite. The tests carried out include: specific gravity test, sieve analysis, Atterberg limits test, compaction test and California Bearing Ratio (CBR). All tests were carried out in accordance with the procedures outlined in BS 1377:1990.

From the results obtained, it was observed that the natural deltaic laterite, when properly compacted, only met the requirements for use as a sub grade material, according to the specifications for road pavement materials by the Federal Ministry of Works (FMW). An optimum river sand content of 30% was seen to improve the CBR of the lateritic soil to above 30% making it suitable for use as sub base layer. Stabilization by addition of plain cement significantly improved the strength of the deltaic lateritic soils with CBR above the 30% minimum required for suitability as a sub base material, and this was achieved at cement contents of about 6% which is in line with the economic ceiling of about 7% specified in the first volume of FMW Specifications on roadworks. However, it fell quite short of the requirement for use as base course material as recommended by the same standard. Stabilization by a mixture of cement and plasticizer - Master Rheobuild 561M , was found to give a considerable improvement over plain cement stabilization and that even at very low    content less than or equal to 2%, depending on the percentage fines and for the mix of laterite/sand/cement as base course layer an optimum mix of 6% cement and 30% sand with laterite was found to yield a CBR value of above 180%. Based on the results obtained from the study, graphical models were presented, which can be used to predict the compaction and strength properties of sand stabilized soils by plotting the percentage fines (F) obtainable from simple gradation tests, particularly wet-sieving against the Optimum Sand Content (OSC). This graphical model however will require further testing to ascertain its viability.