Effect of gradation and testing procedures on the load carrying capacity of calcareous sediments

Abstract

Calcareous sediments are commonly used, in the eastern region of Saudi Arabia as base and subase material for roads and runways. The construction materials are produced from crushers in which materials with different qualities and particle sizes are mixed together and the final product is intended to have a certain gradation. The produced materials have acute water sensitivity. In addition to the upnormal behavior of the calcareous base course materials under the prevailing environmental and loading conditions. The adequacy of use of conventional testing procedures for strength determination of these materials is questionable. This is caused by the poor correlation between the laboratory and the field results as result of discarding the oversize particles for the laboratory samples.

In this search program, the effect of gradation and testing procedures on the load carrying capacity of calcareous sediments (marls) was studied. This was achieved by performing a testing program using the CBR. Unconfined Compressive Strength and Clegg Hammer tests. Three different gradations for two different marls were used in the study. In addition, a large size compaction and CBR testing setup was used to study the effect of oversize particles on the CBR and CIV values. Furthermore, the applicability of the common oversize correction methods was investigated.

The results clearly showed that soil gradation has a remarkable effect on the UCS values while its effect on the CBR and CIV results was not that significant. In addition, the maximum particle size, which was included in the specimens was found to have great significance on the CBR values. Furthermore, the maximum dry density and the optimum moisture content values were found to be independent of soil gradation. The mold confinement was found to have a significant effect on the CBR values. About 100% increase occurred on the CBR values as a result of mold confinement. In addition, CBR values greater than 200% were found to have questionable practicality.

After implementing the oversize correction methods for the selected marls, it was observed that all equations approximated the dry density of the entire material and produced density values close to those obtained using the large mold, with less than 2% tolerances. However, the ASSHTO-1 and ASTM correction equations gave underestimated and overestimated values, respectively. While AASHTO-2 equation and scalp and replace methods gave accurate results.