EFFECT OF GRAVEL CONTENT ON SOIL SUCTION

Abstract

This paper seeks to a) investigate the effect of gravel on soil suction and b) establish whether
results of standard suction tests using filter paper can accurately represent the value of suction that would be
expected in the field. Eight natural soils with different soil gradation and plasticity were used to prepare two
types of specimens: a) the “original” specimens (no change compared to the field soil), and b) “sieved”
specimens – when the “original” soil was passed through a 2-mm sieve to meet the standard requirement.
Comparisons of soil-water characteristics curves (SWCC) obtained for both types of specimens were made to
better understand the effect of gravel content on total and matric suction. The obtained data indicated that the
results of standard tests can significantly overestimate the soil suction. In particularly, it was found that as the
gravel content increased from 4.8 to 19.6%, the difference in suction between the “original” and “sieved”
specimens increased to 14% (total suction) and almost 20% (matric suction). The experimental data showed
that the effect of gravel was more pronounced for low plasticity soils, compared to high and very high
plasticity soils, in which the influence of gravel on suction was found to be insignificant. Although the
“sieved” specimens tended to produce higher values of suction, this tendency might reverse for high and very
high plasticity soils when their liquidity index (LI) became positive.