Fine-grained soils containing diatom microfossils exhibit unique geotechnical behavior due to their biological origins, but their strength properties controlled jointly by diatom content (DC) and stress history remain to be revealed. In this study, reconstituted diatomaceous soil was prepared by mixing pure diatom and kaolin powders in different proportions. These mixtures were subjected to undrained consolidated triaxial shear tests performed using the Stress History and Normalized Soil Engineering Properties (SHANSEP) procedures, revealing how the DC and stress history affect the soil strength. Adding diatoms improved the mixture strength, and a critical DC of approximately 20% was determined, beyond which the normalized undrained strength of the soil was considerably higher than that of common clay without diatoms. Also, a DC higher than 20% associates with the dilatancy of the studied soil with high OCR. Improving the strength of diatomaceous soil by adding diatoms differs essentially from the case of common clay because the plasticity index of the former remains almost unchanged. New formulas incorporating DC and OCR are proposed for predicting the strength of diatomaceous soil, and data for several well-studied soils confirm their validity. This study improves the understanding of fine-grained soils with biological origins and provides important data regarding the mechanical behavior of diatomaceous soil.

The constraining effect of soilbags inhibits soil dilatancy, enhancing the strength and stiffness of the wrapped soil, and resulting in a considerable increase in bearing capacity. This study numerically investigated the macromeso geotextile failure behavior, stress state, fabric anisotropies of wrapped soil and interlocking reinforcement mechanisms of three-layer soilbags under unconfined compression using the three-dimensional discrete element method (DEM). Macroscopically, the failure modes of wrapping geosynthetic depended on the friction between soilbags. With zero friction, failure initiated at the edges of the wrapping geosynthetic; whereas with a friction coefficient of 0.5, failure began in the middle and extended to the edges, showing a progressive failure pattern. Microscopically, the reinforcement of soilbag changed the contact pattern of the particle system from peanut-like to uniformly distributed ellipse. The load transfer to the boundaries caused the occurrence of wrapped soil expansion and geotextile rupture. Additionally, geosynthetic wrapping created an interlocking effect with the surrounding soils, forming a positive feedback to reinforce the wrapped soil before geotextile failure. New understanding on failure modes, stress states, interlocking effect and fabric anisotropies provides a solid foundation for designing reliable and stable soilbag geotechnical permanent protective structures.

The current mechanisms and factors influencing soil aging remain inconclusive and incomplete. Discrete element method (DEM) is adopted to investigate the responses of irregularly shaped granular assemblies subjected to creep and post-creep triaxial shear. The simulated creep and aging behaviours are generally in line with those observed in existing laboratory tests and numerical investigations. In addition to an increase in soil stiffness, the DEM analyses predict an enhanced soil strength as a result of the prolonged interlocking between sand particles during the relatively long creep duration. It is demonstrated that the creep-induced interlocking is directly manifested as a shear resistance above the minimum energy line. The development of interlocking explains the overshooting behaviour observed in post-creep shear. The microscopic responses do not support the aging mechanism based on the buckling of strong force chains. A new hypothesis, termed 'microstructure evolution by stability selection', is proposed to explain soil aging. This hypothesis suggests that interlocking between particles develops naturally during the creep process because interlocked particle clusters generally have a greater chance to survive the particle rearrangement induced by creep, leading to an increased number of interlocked particle clusters in aged soils.

Compacted granular material, integral to geotechnical engineering, undergoes translation, rotation, and interlocking when subject to shear displacements or external loads. The present study focuses on the interlocking of heterogeneous granular materials, a complex behavior influenced by gradation, compaction, and varying particle geometry, and has consequently received limited attention in existing research. To address this research gap, we conducted an analysis on the effect of grain interlocking on the shear resistance of granular assemblies, using a combination of laboratory testing and the discrete element method (DEM). Initially, large-scale direct shear tests were conducted on gravel-sand mixes with varying degrees of compaction and normal pressure. One of the mixes also underwent subsequent shear reversal to explore the differences in grain interlocking between the two shearing processes on the shear plane. After analyzing the laboratory results, a mesoscopic scale investigation was performed by replicating the test using discrete element simulations. To facilitate this, granular particle geometries were measured using 3D laser scanning based on the physical lab tests. Subsequently, based on these scans, discrete element R-block and ball models were utilized to construct both the coarse and fine particles within the mix. Surface vibro-compaction was employed to regulate the degree of compaction. The results indicate that an increase in vertical pressure, coupled with a zero dilatancy angle, results in a rising stress ratio, indicative of grain interlocking. This interlocking exhibits a positive correlation with both the coarse content and the degree of compaction, and varies depending on the shear displacement. As interlocking progresses, the shear band, induced by particle movement, expands and is associated with reduced particle rotation near the shear band. The study further reveals a consistent positive correlation between interlocking and the principal orientation angle of strong normal contact forces, as well as a correlation between interlocking and mobilized contacts. (c) 2024 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Caries is one of the most prevalent human diseases, resulting from demineralization of tooth hard tissue caused by acids produced from bacteria, and can progress to pulpal inflammation. Filling restoration with dental resin composites (DRCs) is currently the most common treatment for caries. However, existing DRCs suffer from low fracture strength and lack comprehensive anti-caries bioactivity including remineralization, pulp protection, and anti-cariogenic bacteria effects. In this study, inspired by plant roots' ability to stabilize and improve soil, fluorinated urchin-like hydroxyapatite (FUHA) with a three-dimensional whisker structure and bioactive components of calcium, phosphorus, and fluorine was designed and synthesized by a dynamic self-assembly method. Furthermore, versatile FUHA particles with different loading fractions were used as functional fillers to fabricate methacrylate-based DRCs, where the urchin-like hydroxyapatite (UHA) filled DRCs and commercial DRCs (Z350XT and BEAUTIFIL II) served as the control groups. The results demonstrated that FUHA with 50 wt% loading in resin matrix endowed DRC (F5) with excellent physicochemical properties, dentin remineralization property, cell viability, promotion of dental pulp stem cells mineralization, and antibacterial properties. Meanwhile, F5 also presented good clinical handling and aesthetic characteristics. Therefore, structure/ functional-integrated FUHA filled DRCs have potential as a promising strategy for tooth restoration and anticaries bioactivity.

Interlocking Compressed Earth Blocks (ICEBs) have recently surfaced as a valuable and innovative inclusion among earthen building materials. They offer workable answers to the common problems with burned bricks and cement blocks. Researchers frequently used river sand in their studies to address and reduce the finer content in soil. This study explored recipes to make ICEBs from construction and demolition wastes. Fine recycled concrete aggregate (FRCA) was used as a soil modification within the ICEBs as a part of this investigation to support ecofriendly, low-carbon product development driven by global climate concerns and the need for improved construction waste management to combat pollution. ICEBs, made by mixing construction and demolition trash, regulate environmental impact and address the scarcity of building materials. Due to the inherent diversity of soil and the lack of a standardized mix design for the manufacturing of ICEB, 40 different mix ratios were generated using the proportionated blends of sand and FRCA. Based on the compressive strength results, the best recipes representing conventional river sand and the FRCA were selected. The prepared samples of ICEBs using the optimized mix recipes of river sand and FRCA were further analyzed for mechanical, thermal, and durability performance alongside the required forensic endorsements, and the test results were enhanced for both ICEBs compared to first-class burnt clay bricks. Sand-incorporated ICEBs achieved 13.72 MPa compressive strength, while FRCA-incorporated ICEBs reached 13.38 MPa. Both ICEBs showed a noticeable improvement in compressive strength compared to various studies. The durability of ICEBs, in terms of water absorption, improved around 70% compared to fired bricks commonly used in the construction industry. The test findings reveal that FRCA incorporated ICEBs showed 14.3% lower thermal conductivity than ICEBs with sand incorporation. Therefore, the use of ICEBs specially designed with FRCA provides the most sustainable alternative to conventional fired bricks used by the construction sector in the developing countries.

The performance of a geogrid-stabilized structure affected by dynamic loadings is significant. This study investigates the microscale deformation mechanism of the geogrid-aggregate interface cyclic shear behavior using the discrete element method (DEM). Spheres and nonspherical clumps are generated to form aggregate samples. The DEM models are able to capture the macroscopic dynamic shear laws of the aggregate layers stabilized with a geogrid in a similar way to those tested experimentally. The microscale mechanical responses of the cyclic shear tests (e.g., shear strain, fabric evolution, and confined zone), which vary with the particle shape as well as the measurement volume, are analyzed. The rib flexural rigidity has a minor influence on the peak shear strength of the geogrid-aggregate interface cyclic shear test, but is a key factor influencing the shape of the hysteretic loop, which is closely related to the micromechanical responses at the geogrid-aggregate interface. The particles in the upper and lower shear boxes show different motion patterns in response to the aperture ratio. In the case of A/ D50 = 2.53, the cumulative plastic deformation of the soil layers extending beyond the interface during the loading and reversal loading process is effectively restrained.