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.

Free swell of compacted plastic soils

“…Soil samples were collected from a depth of 1 to 1.5 m from different construction sites in the Brisbane and Gold Coast area (Queensland, Australia) as part of a study on expansive soils conducted at Griffith University (Liu et al 2017;Gratchev et al, 2018). Physical properties of these soils such as liquid limit (LL) and plastic limit (PL) (ASTM D4318-05, 2005), linear shrinkage (LS) (AS 1289(AS , 2008, maximum dry density (MDD) and optimum water content (OMC) (ASTM D698-00a, 2003) were measured as per guidelines provided in their respective standards.…”