Investigation on Compressibility and Microstructure Evolution of Intact Loess During Wetting Process

Loess is widely deposited in arid and semi-arid areas and is characterized by low dry density, developed pore space, and loose structure, which is not commensurate with that high structural strength and shear strength in the dry state. Many natural phenomena and experimental studies show that intact loess is very sensitive to the change of water content, with slight increases in water content causing a rapid reduction in strength. Abundant information is available in the literature for collapsibility of loess; however, the research on the evolution of loess compressibility during wetting is still minimal, which is very helpful to understand the loess collapsible deformation caused by long-term irrigation. In this paper, the evolution of compressibility of intact loess during wetting are studied by oedometer test, and the microstructure and pore size distribution (PSD) is characterized on intact loess specimens with different water content before and after oedometer tests by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) methods. The results show that the compression index (Cc) and secondary compression index (Cα) of intact loess depend on water content and vertical stress and change abruptly after the vertical stress exceeds the yield stress. The Cα/Cc values of the intact loess are not constant, which increased with the vertical stress to peak and then gradually decreased and tend to 0.025. Both wetting and loading can cause microstructural damage to the intact loess, in which loading leads to the collapse of the overhead structure and transformation from a bimodal PSD into a single PSD, and wetting intensifies the collapse of microstructure to form a compacted interlocking structure and promotes the transformation of medium pores into small pores.

Evaluation of Compression Behaviors of Marine Clay Reinforced with Waste Shredded Tires

This study evaluates the compression behaviors of a soft marine clay reinforced with waste shredded tire (WST) at different sizes (<0.5 mm, 0.5–2.0 mm, and 2.0–4.0 mm) and contents (15%, 35%, and 50%). Results from compression tests indicate that the compression index (Cc) of WST-reinforced soft clay decreases with increasing WST shred size and content. The swelling index (Cs) increases as the WST shred size and content increase. The difference in compression curves becomes more significant for composite reinforced at large shred size. The void indexes of WST-reinforced Lianyungang clay can be well normalized regardless of WST shred size and content by a regression line. The WST dominates the compression behavior of the WST-clay composite, as the WST would be compressed prior to the clay particles. The results in this study provide an optimum WST content at 50% with shred size of 2.0–4.0 mm for reinforcing the Lianyungang marine clay for achieving higher compressibility, contributing to the input database of machine learning for WST-reinforced soil.

Analysis of Geotechnical Characteristics of Coastal Clay Soil Found in Incheon and Gwangyang

Recently, there has been an increase in the number of projects involving the planning and construction of business complex facilities and land development in coastal regions. However, coastal regions are characterized by very soft clay soil. Consequently, such clay soil needs to be augmented for facilitating land procurement. Furthermore, to realize land improvement, the associated geotechnical characteristics need to be analyzed through laboratory tests by acquiring pristine samples of cohesive soil. According to the results obtained from previous studies, the characteristics of the cohesive soil found in Korea can vary depending on the region and depositional environment. The objective of this study is to examine the representative physical and mechanical characteristics of marine clay found in Namhae coast (Gwangyang) and Seohae coast (Incheon) by comparing and analyzing these characteristics. To this end, land examinations were conducted during planning and construction, and data were gathered from 445 sites in Incheon and 844 sites in Gwangyang for comparing the associated physical and mechanical characteristics. Subsequently, by conducting regression analysis, equations of correlation between liquid limit and natural water content, effective surface load and pre-consolidation load, compression index and liquid limit, and compression index and natural water content were deduced. The obtained results indicate that compared to the soil found in Incheon, the clay fraction, natural water content, liquid limit, plasticity index, liquidity index, initial void ratio, and compression index of the soil found in Gwangyang are higher.

Effect of Expanded Polystyrene Particle Size on Engineering Properties of Clayey Soil

The particle size of expanded polystyrene (EPS) has an effect on engineering properties of EPS-clay blends. However, the effect of differences between EPS particle size groups subdivided within 1–3 mm on engineering properties is usually ignored. In this study, different particle sizes of EPS pellets have been considered to separately investigate the effect on the optimum water content (OWC), maximum dry density (MDD), unconfined compressive strength (UCS), ductility, coefficient of permeability, and compression index of EPS-clay blends. Results show that the MDD, ductility, hydraulic conductivity, and compression index of EPS-clay blends do not increase with the increase in the EPS particle size in the range of 0.3–3 mm, while the OWC and UCS do not decrease. For a given EPS content, among samples with the EPS particle size of 0.3–1 mm, 1-2 mm, and 2-3 mm, the MDD and UCS of EPS-clay blends with 1-2 mm in EPS particle size are the largest, while the OWC, ductility, coefficient of permeability, and compression index are the smallest. Microstructure analyses reveal that, for samples with the EPS particle size of 1-2 mm, the pore volume is lower and the microstructure is denser, which are the main reasons why the EPS particle size can influence engineering properties of EPS-clay blends.

Beneficial Use of Water Treatment Sludge in Geotechnical Applications as a Sustainable Alternative to Preserve Natural Soils

This paper explores the feasibility of employing drinking water treatment sludge (WTS) mixed with soils, lime, or rock powder in geotechnical applications, as well as discusses the sustainability of the approach based on experimental results, aiming at the beneficial reuse of waste and the preservation of natural geomaterials. The selected materials were two soils largely used in earthworks, two WTSs, a high purity calcium hydrated lime, and rock powder from a granitic–gneissic quarry, all occurring in São Paulo State, Brazil. The mixtures were chemically, mineralogically, and geotechnically characterized, and the geotechnical properties permeability, shear strength, and deformability were investigated. Soil-WTS mixtures showed hydraulic conductivity (10−10–10−6 m/s, depending on soil and WTS), effective cohesion (10–30 kPa), friction angle (34°–40°), undrained strength (>50 kPa), and compression index (0.1–0.4) compatible with those of soils usually employed in earthworks. Lime:WTS and rock powder:WTS mixtures achieved 50 kPa undrained strength for WTS contents lower than 24% and 8%, respectively, and could be used as daily and intermediate covers of waste landfills, as well as in other applications with low soliciting stresses. The possibility of WTS being pumped instead of transported by trucks was analyzed in the light of results from rheological tests.

Mechanical and permeation response characteristics of basalt fibre reinforced tailings to different reinforcement technologies: an experimental study

Tailings dam is a man-made hazard with high potential energy; dam failure would cause great losses to human lives and properties. However, the limitations of conventional reinforcement methods like geosynthetic make it easy to slide along the weak structural plane. In this paper, we innovatively added basalt fibre (BF) with different lengths ( l ) and contents ( ω ) into tailings to study its mechanical and permeation characteristics. The results indicate that BF can improve the shear strength ( τ ), cohesion ( c ) and compression index ( C c ) of tailings, but it has little effect on internal friction angle ( φ ). When l is constant, τ , c and C c are positively correlated with ω . One notable phenomenon is that τ and c do not constantly increase with l when ω is constant, but obtain the maximum under the optimal length of 6 mm. Moreover, when ω > 0.6%, permeability coefficient ( k ) is greater than that of the original tailings and the sensitivity of c , φ , τ , C c , k to fibre content is greater than that of length. The research results facilitate the understanding of BF reinforced tailings, and could serve as references for improving the safety of tailings dam and other artificial soil slopes or soil structures.