Seasonal Variations of a Subgrade Soil Resilient Modulus in Southern Brazil

Abstract

The influence of suction on the resilient modulus of a shale residual lateritic soil was analyzed. Laboratory tests were carried out to obtain the moisture content-suction relationship and determine the resilient moduli of specimens submitted to drying, wetting, or wetting-after-drying paths. A supplementary study on the effects of compaction method on soil resilient modulus was carried out. Soil suction was measured in situ, with jet-fill tensiometers installed along test sections built in a pavement testing facility. Test sections were loaded by a traffic simulator, and periodically deflections were measured for modulus backcalculation. Laboratory and in situ results confirmed the consensus that suction remarkably affects soil elastic deformability. Wetting-after-drying paths proved to be an extremely severe condition that may lower resilient modulus up to four times. Static compaction led to resilient moduli higher than those of specimens compacted dynamically or by kneading. In situ results matched reasonably well with laboratory moduli of specimens compacted by kneading and tested at optimum moisture content. In general, the importance of drainage design and maintenance was clearly confirmed. In well-drained pavements, subgrade soils will not be saturated for long periods. Suction will control stress state and soil deformability and guarantee that the pavement will carry the designed traffic before failure.