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.
Abstract. This paper discusses the influence of structure in the soil-water characteristic curves (SWCC) of two residual soils of granite formed in a subtropical environment. One soil has a saprolitic nature (named GrSp) and the other shows lateritic behavior (named GrLt). Both materials occur on a slope which presents a extensive history of landslides in the municipality of São José, Southern Brazil. SWCC of undisturbed and remolded specimens were determined using the filter-paper technique. Undisturbed specimens were collected and remolded specimens were produced by static compression of disintegrated soil to the same void ratio and moisture content of undisturbed specimens. SWCC of saprolitic soil showed curves which were modelled as unimodal but the lateritic soil required the use of bimodal curves because of the structure developed in micro and macro levels. Suction levels measured in GrLt soil were higher than in saprolitic soil. Remolding process changed the levels of suction achieved, which is due to the structure and more specifically to the size of pores in the remolded soils. Hysteresis were verified in both materials, but were far more pronounced in the lateritic soil. Analysis of mercury intrusion porosimetry were carried out in GrSp soil. They showed that remolding generates a different pore distribution from the existing in the undisturbed soil.
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