Biomasses are organic materials that are derived from any living or recently-living structure. Plenty of biomasses are produced nationwide. Biomasses are mostly combusted and usually discarded or disposed of without treatment as biomass ashes, which include wood and sugarcane bagasse ashes. Thus, recycling or treatment of biomass ashes leads to utilizing the natural materials as an economical and environmental alternative. This study is intended to provide an environmental solution for uncontrolled disposal of biomass ashes by way of recycling the biomass ash and replacing the soils in geotechnical engineering projects. Therefore, in this study, characteristic tests of wood and sugarcane bagasse ashes that are considered the most common biomass ashes are conducted. The test of chemical compositions of biomass ashes is conducted using energy dispersive X-ray spectroscopy (EDS), and Scanning Electron Microscope (SEM), and heavy metal analysis is also conducted. Engineering behaviors including hydraulic conductivity, constrained modulus and shear modulus are examined. Also, coal fly ash Class C is used in this study for comparison with biomass ashes, and Ottawa 20/30 sands containing biomass ashes are examined to identify the soil replacement effect of biomass ashes. The results show that the particle sizes of biomass ashes are halfway between coal fly ash Class C and Ottawa 20/30 sand, and biomass ashes consist of a heterogeneous mixture of different particle sizes and shapes. Also, all heavy metal concentrations were found to be below the US Environmental Protection Agency (EPA) maximum limit. Hydraulic conductivity values of Ottawa 20/30 sand decrease significantly when replacing them with only 1%–2% of biomass ashes. While both the constrained modulus and shear modulus of biomass ashes are lower than Ottawa 20/30 sand, those of mixtures containing up to 10% biomass ashes are little affected by replacing the soils with biomass ashes.

Water-repellent soils have a potential as alternative construction materials that will improve conventional geotechnical structures. In this study, the potential of chemically treated water-repellent kaolin clay as a landfill cover material is explored by examining its characteristics including hydraulic and mechanical properties. In order to provide water repellency to the kaolin clay, the surface of clay particle is modified with organosilanes in concentrations (C_O) ranging from 0.5% to 10% by weight. As the C_O increases, the specific gravity of treated clay tends to decrease, whereas the total organic carbon content of the treated clay tends to increase. The soil-water contact angle increases with an increase in C_O until C_O = 2.5%, and then maintains an almost constant value (≈134.0°). Resistance to water infiltration is improved by organosilane treatment under low hydrostatic pressure. However, water infiltration resistance under high hydrostatic pressure is reduced or exacerbated to the level of untreated clay. The maximum compacted dry weight density decreases with increasing C_O. As the C_O increases, the small strain shear modulus increases, whereas the effect of organosilane treatment on the constrained modulus is minimal. The results indicate that water-repellent kaolin clay possesses excellent engineering characteristics for a landfill cover material.

The presence of nano-sized particles on the surface of sand grains can significantly influence the mechanical, physical, and chemical behavior of the sand because of the effects of contacts between particles. This study quantified the change in small strain stiffness caused by the presence of iron oxide particles (hematite and goethite) that were chemically sorbed onto uncemented silica sand. Particularly, the change in contact mode between sand particles, caused by the presence of the nanoparticles, was studied. The iron oxide coating density of coated sands was controlled by changing the substrate sand particle size, ranging from 0.11 to 0.72 mm in diameter, with corresponding iron contents ranging from $0.13\hspace{0.17em}\text{mg iron oxide}/\text{g sand}\hspace{0.17em}\left(\text{goethite}\right)$ to $6.4\hspace{0.17em}\text{mg iron oxide}/\text{g sand}\hspace{0.17em}\left(\text{hematite}\right)$ . The presence of the iron oxide nanoparticles altered the contact mode between particles and, correspondingly, the small strain stiffness as a function of the initial relative density, applied stress, iron content, and substrate particle size. The macroscale experimental results were analyzed via contact mechanics (i.e., Hertz and Mindlin contacts) to gain a more fundamental understanding of changes that iron oxide coatings make on the behavior of sand.