The study of the strength of reconstituted and stabilised soft soils is very important in geotechnical engineering. The soil particles, such as clay, sand, and silt play important roles in determining the behaviour of soils. The behaviour of clay and sand particles are unique; however, the behaviour of silt particles lie in a transitional form between sand and clay. Therefore, this paper seeks to investigate (a) the effect of silt contents on the strength of soft soils; (b) the effect of silt content on the strength of cement-stabilised soft soils; and (c) the microstructure of the soft soil specimens stabilised by cement with varying particle size distribution. A series of tests consisting in consolidated, isotropic undrained (CIU) triaxial tests, unconfined compressive strength (UCS) tests, and scanning electron microscope (SEM) images were conducted in this study to achieve these objectives. In conclusion, the relationship between the silt content and critical state behaviour of soft soils (both clay and silt particles) are proposed. For the cement-stabilised specimens, the unconfined compressive strength increases with the increase in silt content when the cement content is 10%. However, the UCS decreases with the increase in silt content when cement content is 30%. With cement content ranging from 15–25%, the UCS increases at first with the increase of silt content but decreases once the silt content reaches a ‘saturation’ point.

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.