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Geotechnical structures made of granular material tend to be unsaturated during their service life. However, there is presently a lack of sufficient research and studies on their volumetric behavior under unsaturated conditions. In this study, loading and wetting induced volumetric behavior of granular materials in the unsaturated state was studied within a moisture content-based framework. Recycled crushed brick (CB) and excavation waste rock (WR) were the granular materials used in this research to promote sustainable construction. Several loading, unloading, and wetting state paths were investigated with respect to virgin compaction surfaces (VCS) developed using groups of compaction curves. The obtained experimental data was utilized to develop a constitutive model capable of predicting wetting-induced volume changes of granular materials in a net stress range of 100–4000 kPa and gravimetric moisture content range of 3.6% for WR, and 7.5% for CB to saturation. The model was verified by undertaking several independent state paths on independent materials and comparing the experimental responses with those predicted using the model. The proposed model is featured with simplicity in acquiring the model input parameters with the aim of filling the existing gap between the theoretical and real-life application of unsaturated soil mechanics. An application of the model can be the basis for the prediction of the settlement of a granular geotechnical structure that is being externally loaded and is subject to changes in moisture content due to climatic effects.

It is believed that the relative density (Dr) can affect the internal stability of the gap-graded soils and hence the erosion of their fine particles (i.e. susceptibility to suffusion). This paper investigates the influence of Dr on the contribution of fine particles to soil fabric. A new procedure is proposed to produce samples with target Dr using the discrete element method (DEM). DEM simulations were carried out using spherical particles. Particulate scale analysis of variation of stress reduction factor (αDEM), the evolution of contact type and fine particle coordination number (Zfine) with Dr reveals how Dr affects packing stability. The results show that packings with a fine content of 35% and the gap ratio in a range of 4–7 are in the transitional zone in which they are unstable initially and become internally stable as Dr increases. The behaviour of gap-graded soil in the transitional zone is governed by fine-coarse contacts, but fine-fine contacts dominate the behaviour when soil becomes internally stable. Both αDEM and Zfine are reliable parameters in determining internal stability of gap-graded soils. Finally, the correlation between the results and macro-scale matrix phase diagrams confirms the validity of micro-scale information to describe the underlying phenomenon.

Loose granular soils placed during a land reclamation process require densification to enhance their engineering properties. In a mega-land reclamation project in the Republic of Singapore, techniques such as Muller resonance compaction (MRC), vibroflotation, and dynamic compaction were employed to densify the land reclamation sand fills. The efficacy of densification was subsequently verified by cone penetration tests (CPT). The MRC technique results in the sand mass being rearranged due to the application of high vibrating energies. The vibroflotation technique results in a densified column of soil forming at and surrounding the probe point. The dynamic compaction technique results in the centroid point being the most compacted point, provided the selected spacing is efficient. The aging effect in the vibroflotation technique was found to be significant, in contrast to the MRC and dynamic compaction techniques. The usage of these three deep compaction techniques was found to be effective for the densification of deep deposits of loose sand fills in this mega-land reclamation project.