Temperature is a key factor influencing the mechanical behavior of the static interface between marine silica sand (SS) and geogrid, which directly impacts the stability and bearing capacity of reinforced soil structures. Despite its importance, there is limited research on the temperature-dependent mechanical properties of the silica sand-geogrid (SG) interface. To address this, a self-designed temperature-controlled large-scale static shear apparatus was used to perform a series of static shear tests on the SG interface, utilizing marine SS particles ranging from 0.075 mm to 2 mm and testing temperatures ranging from -5 degrees C to 80 degrees C. The results revealed a non-linear relationship between shear strength and temperature: as temperature increased from -5 degrees C to 40 degrees C, shear strength decreased, then rose between 40 degrees C and 50 degrees C, before declining again beyond 50 degrees C. The sensitivity of interface shear strength to variations in normal stress remained low at both low and high temperatures. Moreover, the interface friction angle and cohesion showed temperature-dependent fluctuations, initially decreasing, then increasing, and finally declining again. These findings underscore the complex effects of temperature on SG interface mechanics and suggest that temperature must be carefully considered in evaluating the stability and performance of reinforced soil structures under varying environmental conditions.

Granular soils creep and age. Previous findings on the time-dependent phenomena under deviatoric stress are summarized and extended with the results of an experimental investigation. Multi-stage triaxial compression tests with creep phases at different deviatoric loading on medium-dense and dense samples of a uniformly graded silica sand confirm an increase in stiffness after creep phases. Contact maturing, contact homogenization, and stabilization of the soil structure are known causes for ageing reported in the literature. As other results found in the literature, the volumetric creep behavior can be dilatant, contractant or of negligible strain close to zero and depends on the trend of the volumetric strain resulting from deviatoric loading at the beginning of creep. By the triaxial tests it is shown that dilatant creep results in an increase of the radial strain due to grain rearrangements. The axial strain rates during creep and changes of the small-strain shear modulus (ageing) follow a power law with time. According to the experiments, the exponent of the proposed power law describing the development of strain and shear modulus at small strain during creep is independent of the density and stress state. The small-strain shear stiffness and the associated soil structure at the onset of creep determine the subsequent ageing behavior. A linear dependency was found between the related ageing rates and axial strain rates during creep, which can be used to predict ageing of granular materials in combination with rate-dependent constitutive models.

Microbial-induced calcite precipitation (MICP) is an environmentally friendly treatment method for soil improvement. When combined with carbon fiber (CF), MICP can enhance the liquefaction resistance of sand. In this study, the effects of CF content (relative to the sand weight of 0%, 0.2%, 0.3%, and 0.4%) on the liquefaction resistance of MICP-treated silica and calcareous sand were investigated. The analysis was conducted using bacterial retention test, cyclic triaxial (CTX) test, LCD optical microscope, and scanning electron microscopy (SEM). The results showed that with the increase in CF content, the bacterial retention rate increased. Additionally, the cumulative cycles of axial strain to 5%, excess pore water pressure to initial liquefaction, as well as strength and stiffness, all increased with higher CF content. This trend continued up to the CF content of 0.2% for silica sand and 0.3% for calcareous sand, beyond which the cumulative cycles began to decrease. The great mechanical system of CF, calcite, and sand particles was significantly strengthened after MICP-treated. However, the reinforced calcite did not completely cover the CF, and excess CF hindered the connection between sand grains. The optimal amount of CF in silica and calcareous sands were 0.2% and 0.3%. This study provides valuable guidance for selecting the optimal CF content in the future MICP soil engineering.

Changes in particle granulometry could lead to significant changes in a soil's behavior, making an understanding of micro-scale granulometry essential for practical applications. Changes in particle size, shape, and particle size distribution could result from a combination of applied normal and shearing stresses, which can in turn influence further response of the material. This study explored particle breakage during both compressive and shear loading under typical stresses. A deeper understanding of the phenomenon requires distinguishing broken and unbroken grains at the particle scale. Dynamic Image Analysis (DIA) was therefore employed to quantify changes in particle granulometry in two sands, a siliceous Ottawa sand and a calcareous sand known as Fiji Pink. Pre-sorted specimens having similar size, granulometry, and particle size distributions were tested using both oedometric and direct shear tests having the same aspect ratio, facilitating a direct comparison of the effects of shearing and compression on similar materials having different mineralogy. A breakage index was used for prognosis of particle breakage at key reference diameters. During oedometric tests, grain breakage was limited in both sands at stresses up to 1.2 MPa, but it increased significantly during direct shear tests. A conceptual model was proposed to explain the particle breakage mechanism during shear, at four key phase points representing (1) maximum compaction, (2) transition from compaction to dilative behavior, (3) maximum shear stress, and (4) peak test strain. In addition, a loading intensity framework was adopted to explain the relative roles of normal and shearing stresses on particle breakage. An increase of fines in soil during shearing was also observed and related to two sources: coarser grain abrasion and finer particle crushing. The vulnerability of grains with more anisotropic shapes was also observed. The loading intensity framework suggested that attrition of particle diameter could be divided into two phases, with a transitional critical loading intensity that appeared constant for each sand. For Ottawa sand, abrasion was the primary mechanism observed, causing a significant increase in Aspect Ratio (AR) and Sphericity (S) for finer grains. For Fiji sand, a transition from abrasion to attrition was noted, leading to limited sphericity decrease for the largest particles. Finer particles cushioning larger Fiji sand particles are more prone to breakage, resulting in increased AR and S. Finally, test results were used to propose a simple hyperbolic model to predict evolution of the particle size distribution during shear, for sands. The model was also verified using published data on grain evolution during shear of a different sand, not employed in its development.

Electrolysis desaturation is an emerging ground improvement technique with significant potential for widespread application in liquefaction mitigation. This method reduces the saturation of foundation soils, thereby decreasing soil liquefaction potential during earthquake. To date, there is still a lack of systematic research on the microstructure evolution of silica sands during the electrolysis desaturation treatment. In this study, non-destructive low-field nuclear magnetic resonance (NMR) technology was employed to investigate the effects of electrolysis desaturation on the silica sands at the microscale. The results showed that the electrolysis desaturation treatment had negligible effects on the structures of micropores and mesopores. The macropores in fine sand expanded during electrolysis, and the increasing current amplified the extent of this expansion. Conversely, in coarse sand, the macropores contracted during electrolysis. Bubbles generated by high-current electrolysis tend to aggregate, causing cracks and surface uplift in the fine silica sand. For the coarse silica sand, the generated gas accumulates within the existing voids, resulting in an insignificant impact on the soil structure. The electrolysis desaturation treatment primarily facilitated the expulsion of free water in both fine and coarse silica sands. In fine silica sand, employing a high current can reduce saturation more effectively within the same duration, but it also allows for more gas bubbles to escape after resting. Coarse silica sand maintained a high desaturation efficiency due to its greater porosity. This study provides a rational explanation in microscale of the structural impacts of electrolysis desaturation treatment on foundation soils.