The mitigation of seismic soil liquefaction in sand with fine content presents a challenge, demanding efficient strategies. This research explores the efficacy of Microbial-Induced Partial Saturation (MIPS) as a biogeotechnical technique to improve the liquefaction resistance of sandy soils with plastic fines. By leveraging the natural metabolic processes of indigenous microorganisms, this method introduces biogenic gas production within the soil matrix, effectively reducing its degree of saturation. This partial desaturation alters the soil's response to cyclic loading, aiming to mitigate the risk of liquefaction under dynamic loading conditions. Experimental results from a series of undrained strain-controlled cyclic shear tests reveal that even a modest reduction in saturation significantly enhances the soil's stability against seismic-induced liquefaction. The investigation extends to analyzing the effectiveness of the MIPS treatment in sands with low-plasticity clay content, offering insights into the interaction between microbial activity, soil texture, and liquefaction potential. Results show that while plasticity plays a key role in improving the cyclic response of soils, the influence of MIPS treatment remains noteworthy, even in sand with plastic fines. Additionally, a modified predictive formulation is introduced, incorporating a calibrated parameter to account for the influence of fines' plasticity on excess pore pressure generation.

If building loads cannot be transferred into the soil, ground improvements are often used, which require the addition of cement with considerable emissions of CO2. Thermo-mechanically processed crushed concrete fines can partially replace the required cement. This article deals with comprehensive laboratory tests to improve the soil mechanical properties of a typical sand as a building ground and demonstrates the applicability of thermo-mechanically processed concrete fines for the substitution of 25 wt.-% to 50 wt.-% of cement for practical construction purposes. Processing temperatures of 400 degrees C and 600 degrees C proved to be particularly effective, with greater reductions in strength and stiffness occurring outside this temperature range.

Given the insufficiency in research on the mechanism of fine particle impact on gravelly soil subgrade deterioration, a series of saturated gravelly soil consolidated drained triaxial shear tests was conducted using the GDS triaxial testing system under varying fines contents and effective confining pressures to investigate the effect of fine particle contamination on the static shear characteristics of gravelly soil. The results indicate that: (1) As the fines content increases, the stress-strain curve development pattern transitions from strain softening to strain hardening, with a critical threshold at a fines content of Fc=15%. (2) The addition of fine particles leads to a decrease in the principal stress ratio, brittleness index, peak strength, cohesion, and internal friction angle of the gravelly soil, while the degradation indices increase. The relationship between the degradation indices of peak strength and cohesion and fines content can be described by quadratic functions, and the degradation index of the internal friction angle by a cubic function. (3) With increasing fines content, critical state parameters decrease. The effective stress path shows retracing behavior, becomes shorter, and shifts to the left. (4) The addition of fine particles results in a decrease in the secant modulus, and the volumetric strain-axial strain curve changes from contractive-dilative to purely contractive.

Evaluating cyclic liquefaction of soil from the perspective of energy dissipation provides a more comprehensive insight into its liquefaction mechanism. This study conducted a series of undrained cyclic triaxial tests using discrete element method to investigate the influence of plastic fines content (FC) on the dynamic characteristics of sand-clay mixtures. A new evaluation index, the Viscous Energy Dissipation Ratio (VEDR), is introduced to assess the energy dissipation performance of sand-clay mixtures. Macroscopically, it is shown that when FC 30 %, the trend reverses. In terms of energy dissipation, as the fines content increases, VEDR gradually transitions from the sand-like to the clay-like mode, exhibiting a unique transitional mode when FC = 50 %. Microscopically, the development of bond breakage is highly similar to that of VEDR. The bond breakage facilitates particle sliding and rolling, which is the fundamental factor causing the differences of energy dissipation between pure sand and sand-clay mixtures. This paper contributes to the mechanistic study of liquefaction criteria based on energy theory by establishing the connection between microscopic particle behavior and macroscopic energy dissipation during the cyclic liquefaction process.

When loose, saturated sands and non-plastic silts are subjected to undrained cyclic loading, they will generate positive pore pressures. This increase in pore pressures leads to a decrease in effective stress with a corresponding decrease in shear strength and increase in liquefaction susceptibility. For combinations of sand and non-plastic silt, the threshold fines content can be defined as the non-plastic silt fines content at which the soil changes from sand-like behavior to silt-like behavior. Soils below the threshold fines content behave like sands and soils above the threshold fines content behave like silts. During cyclic triaxial and cyclic direct simple shear tests performed on specimens of sand and silt prepared to the same relative density but different fines contents, two rates of pore pressure generation were observed. When compared at five cycles of loading, soils with silt contents above the threshold fines content were found to produce pore pressure ratios as much as 50% higher than those observed for soils with silt contents below the threshold fines content. When evaluated in terms of cycles, cycle ratio, and dissipated energy ratio, the rate of pore pressure generation was found to be more rapid for soils above the threshold fines content than for soils below the threshold fines content.

Internal erosion involves the transport of soil particles from within or beneath a geotechnical structure due to seepage flow, influencing the subsequent mechanical and hydraulic behaviour of the soil. However, predicting changes in small-strain modulus ( G max ) with eroded fines and varying principal stress directions can be challenging due to various factors related to soil fabric. The present study investigates the impact of seepage flow on G max , as well as the effect of principal stress rotation (PSR), of gap-graded soil with a fines content of 20%, using a novel erosion hollow cylindrical torsion shear apparatus. The erosion test results indicate that, regardless of density, the G max generally increases with seepage time. The trend of G max measured in the vertical and torsional directions varies significantly, as seepage is applied always downward, resulting in a different impact on the vertical and horizontal bedding planes. After a cycle of PSR, the induced torsional shear strain is found larger for the eroded specimens, while vertical strain decreases due to fine removal accompanied by seepage flow. In the PSR tests, the specimens subjected to erosion exhibit a greater reduction in G max compared to non- eroded specimens, with increasing the angles of principal stress direction. This reduction may be due to the inefficacy of the reinforced soil skeleton established by erosion against shearing. The distribution of fine particles and anisotropy induced by seepage flow contribute to non-trivial mechanical behaviour during principal stress rotation, particularly regarding small-strain shear modulus. (c) 2024 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Evaluating the cyclic strength development using energy-based methods is a novel concept in studying the dynamic properties of sand-clay mixtures under cyclic loading. In this study, a series of undrained cyclic triaxial tests were conducted on sand-clay mixtures, and the performance of different fine-grain contents on the dynamic properties and the energy dissipation of sand-clay mixtures was investigated based on the energy-based methods. The results demonstrated a gradual increase in the cyclic strain amplitude and the residual axial strain with increasing fines content (FC) under cyclic loading with a controlled cyclic stress ratio; in contrast, the accumulation of pore-water pressure slowed down. An initial decrease in the cyclic strength of the mixtures was observed with an increase in their fines contents; however, further increasing the FC enlarged the cyclic strength of the sand-clay mixtures. This transition was observed when the threshold fines content reached about 30%. The viscous energy dissipation ratio (VEDR), which is a nondimensional energy ratio based on the relationship between cyclic stress and strain and reflects the characteristics of dynamic properties, was utilized to compare three critical phase transition points, namely, VEDRvalley, VEDRpeak, and VEDR5%strain, in the energy dissipation of the sand-clay mixtures. Based on the VEDR results, the cyclic strength development indexes were established. Furthermore, low-vacuum environmental scanning electron microscopy revealed that as the FC increased, the particle composition of the sand-clay mixtures transitioned from predominantly coarse-grained to fine-grained, resulting in a change in the cyclic behavior of the mixtures from sandlike to claylike. The cyclic strength development indices provided further insights into and quantified the effect of fines contents of the sand-clay mixtures on their cyclic strength development process.

Microbially induced calcium carbonate precipitation (MICP) technology is an emerging and environmentally sustainable method for improving the strength and stiffness of soil. Specifically, this innovative approach has gained favor in marine engineering due to the advantaged compatibility between precipitated calcium carbonate induced by MICP and coral sand. Sand containing fines is susceptible to liquefy. Whereas, the impact of fines contents on cyclic behavior of MICP-treated calcareous sand remains uncertain. Consequently, this technical note aims to investigate the liquefaction behavior of biocemented calcareous silty sand by conducting undrained cyclic triaxial shear tests and microscopic analysis. The results revealed the patterns of the excess pore water pressure curves and cyclic deformation characteristics as the fines contents increased. The liquefaction resistance of biocemented sand initially decreases with the addition of fines but subsequently exhibits an increasing trend. Microscopic analysis showed that at the cementation level with the cementation solution concentration of 1 mol/L, the calcium carbonate crystals are mainly attached to the surface of sand grains and this pattern does not directly affect the force chain.

This paper presents a specifically designed experimental study aimed at exploring the role of fines in altering the behaviour of sand under the constant shear drained (CSD) stress path. The novelty of this study includes that the interplay of several key factors (fines shape, fines content, void ratio) was investigated systematically and the true constant shear stress condition was fulfilled by means of an advanced servo system which allowed the entire loading response to be captured. One of the marked findings is that the presence of fines not only alters the onset of instability of loose sand but also affects the deformation development thereafter. Drained instability can be triggered more easily in loose sand mixed with silica fines compared with the sand on its own. At the same quantity of fines, instability can be triggered more easily for sand mixed with rounded fines. However, the effect of fines appears to be marginal for sand at dense state. For all tested specimens, values of the axial strain rate at instability fall in a narrow range (0.008%/min-0.016%/min), meaning that the axial strain rate can be potentially a useful guide for quantitatively determining the inception of instability under the CSD conditions. The stress ratio q/p ' at onset of instability under the CSD conditions is also state dependent as under the undrained conditions.

This study investigates the geotechnical performance of municipal solid waste fines (MSWF) stabilized with xanthan gum and agar gum. As urbanization escalates, the challenge of managing MSW becomes more critical, especially in India, projected to produce up to 436 million tonnes annually by 2050. Landfill mining yields material with poor engineering properties, necessitating effective stabilization techniques. This research evaluates the efficacy of xanthan and agar gums in enhancing the geotechnical properties of MSW fines. Various tests, including compaction, triaxial, and unconfined compressive strength, were conducted on samples subjected to different curing periods. The results indicate a substantial improvement in the mechanical properties of MSW fines treated with agar gum, including a maximum increase of 58% in unconfined compressive strength (UCS). Microstructural examinations confirm enhanced interparticle bonding, while leachate analysis shows a notable reduction in heavy metal release. Statistical assessments underscore the significance of curing time in determining the final properties of the treated MSW fines. Overall, agar gum emerges as a more effective biopolymer for MSW fines stabilization, with curing duration playing a vital role in achieving optimal geotechnical characteristics. These findings offer valuable insights for selecting appropriate bio-treatment methods for heterogeneous materials like MSW fines.