Sand aging, defined by time-dependent increases in stiffness and strength over periods ranging from days to months, poses significant challenges in geotechnical engineering and soil science. Despite its relevant implications, the mechanisms driving sand aging remain understood. This review systematically examines sand aging, emphasizing the classification of chemical and mechanical processes involved. Key advancements in chemical aging understanding, particularly the influence of surface chemistry and electrokinetic forces, are discussed. Additionally, the review underscores the critical role of micromechanical modeling, especially discrete element methods, in elucidating particle interactions and aging phenomena. The review also identifies essential directions for future research, notably incorporating particle shape and surface texture into aging models. Hence, this comprehensive resource aims to enhance the understanding of sand aging.

Creep is recognised to be an important physical property of soils, exerting a profound influence on the stability of structures. In order to gain a comprehensive understanding of the advancements and focal points in soil creep research, the relevant literature was accessed from the Web of Science Core Collection database, totalling 3907 papers (as of 25 March 2024). Statistical analyses on publication volume, keyword co-occurrence, and clustering were conducted using the visualization software VOSviewer (1.6.20). The current hotspots in soil creep research were identified, and a systematic review was undertaken on the influencing factors of soil creep and the corrective methods of creep models. The research findings indicate that the number of papers on creep research exhibits a trend of increase followed by a decrease over time. Developed countries, such as those in Europe and America, initiated research in this field earlier than developing countries like China. Currently, the research focus is primarily centred on creep models. Significant differences exist in the creep deformation of soils under different influencing factors, with soil microstructure, moisture content, and stress path being important factors affecting soil creep deformation. Creep deformation in unsaturated soils primarily considers the influence of matric suction, while indoor creep tests are mainly conducted based on vertical loading, which differs significantly from the stress conditions experienced by soils in engineering construction sites. Currently, adjustments to soil parameters are mainly made through single-factor adjustments involving stress, time, damage, and matric suction to determine creep models under specific influencing factors, and then to modify the models accordingly. However, research on the creep deformation mechanism and creep models under multiple factors is relatively limited. Future research directions are expected to focus on the microscopic scale of creep mechanisms and multi-factor creep models.

Creep of granular soils is frequently accompanied by grain breakage. Stress corrosion driven grain breakage offers a micromechanically based explanation for granular creep. This study incorporates that concept into a new model based on the discrete element method (DEM) to simulate creep in sands. The model aims for conceptual simplicity, computational efficiency and ease of calibration. To this end a new form of normalized Charles power law is incorporated into a DEM model for rough-crushable sands based on the particle splitting technique. The model is implemented using a controlled on-off computational strategy. The model is validated by simulating creep in quartz sands in oedometric and triaxial conditions. Model predictions are shown to compare favourably with experimental results in terms of creep strain, creep strain rates and particle breakage. The model proposed would facilitate the calibration of phenomenological continuum models, but may be also useful to directly investigate structural scale phenomena, such as pile ageing.

Low-pressure injection of nanosilica aqueous suspensions is often adopted to either waterproof or increase the liquefaction resistance of granular soils. The basic principle behind this ground improvement technique consists in filling the soil pores with a low-viscosity fluid that changes its consistency with time, first into a gel, then into a solid. From an application point of view, the simulation of the time-dependent permeation process is crucial to relate the in situ distance covered by the grout to the operational parameters. A comprehensive investigation was performed, combining laboratory experiments with theoretical approaches, to characterize the phenomenon and then derive predictive relations useful for designing treatment executions. The time-dependent rheological properties of different nanosilica aqueous suspensions were first quantified by means of rheometric tests, then described with Bingham's law. Grout permeation in granular media was then simulated by suitably modifying Darcy's law to incorporate the temporal evolution of Binghamian grout rheology. After validating the modified Darcy's law employment for nanosilica grout flows with respect to laboratory experimental data, simplified analytical equations, capable of predicting the temporal evolution of the distance covered in situ by the grout and the flow rate-injection pressure relation, are provided. Nanosilica aqueous suspensions are environmentally nontoxic materials with the consistency of a low-viscosity fluid, suitable for injections into fine-graded soils, but, when mixed with a sodium-chloride solution, they transform with time into a gel of solid consistency. Thanks to these properties, they are frequently adopted to provide a fast remedial against piping induced by excavation, seal contaminants or reduce the liquefaction potential of sands. Nanosilica grout is commonly injected at low pressure, leading to filling soil pores during seepage. The previously mentioned transient evolution of the suspension rheological properties, controlled by nanosilica and sodium-chloride proportions, starts during the injection-seepage phase, playing a paramount role in affecting the geometry of the treated soil domain. The present work provides an accurate description of the time-dependent grout rheology and a predictive seepage analytical tool to simulate the diffusion of nanosilica grouts, characterized by variable compositions and injected from sources of different geometrical layouts into homogeneous soils with different grain size distributions. This tool allows tailoring of the injection parameters (pump pressure, nozzle spacing, injection time) on in situ soil hydraulic properties and rheology of the selected nanosilica suspension.