Compressibility and microstructure of compacted laterites

Tropical soils are abundant in several equatorial South American countries. The laterites located in the high plain of central Brazil are one example of these tropical soils. This zone, dominated by the Tocantins complex, has metasedimentary rocks which are affected by the extreme environmental conditions produced by the region's two marked dry and wet seasons. This paper presents a laboratory study about the behaviour of this compacted lateritic soil that is currently used in Brasilia as a subgrade for roads and embankments. In their natural state, 65% of the mass of these soils is in the form of aggregates of smaller particles which exhibit great collapsibility. A total of 102 samples were compacted with different water contents and energies using the Proctor procedure, afterwards their microstructural and compressibility characteristics were studied. Microstructural states were studied using a mercury intrusion porosimeter, and oedometric compression tests were carried out under different conditions of suction and saturation using the osmotic technique. From the microstructural point of view, all the samples show a bimodal pore size distribution and the shape of the pore distribution curve changes during compression. The results show that the microstructure is strongly related to mechanical behaviour.