EFFECT OF GRAVEL CONTENT ON SOIL SUCTION

: This paper seeks to a) investigate the effect of gravel on soil suction and b) establish whetherresults of standard suction tests using filter paper can accurately represent the value of suction that would beexpected in the field. Eight natural soils with different soil gradation and plasticity were used to prepare twotypes 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 tobetter understand the effect of gravel content on total and matric suction. The obtained data indicated that theresults of standard tests can significantly overestimate the soil suction. In particularly, it was found that as thegravel 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 showedthat the effect of gravel was more pronounced for low plasticity soils, compared to high and very highplasticity 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 veryhigh plasticity soils when their liquidity index (LI) became positive.