Discrete element method (DEM)-based numerical models in the YADE environment are used to simulate the constitutive response of uncemented and bio-cemented sands to investigate the influence of boundary conditions, loading and testing conditions, and material types. Both the classical DEM model and the pore scale finite volume (PFV)-coupled DEM model are used to simulate the response of saturated uncemented and lightly cemented sands with a rigid wall boundary under both drained and undrained triaxial compression. A DEM model with flexible boundaries created using particle facet (PFacet) elements is used to simulate undrained triaxial compression of moderately cemented sands, including the influence of confining stress. The PFacet-based model is used to predict the transition from barreling failure to shear banding when the confining stress or the cementation degree increases. The classical DEM model with cohesive bonds of uniform strength is also used to successfully simulate the uniaxial compression response of a sand with an extremely high degree of cementation. Finally, this paper presents a particle-packing model consisting of multiple solid phases for cemented sands based on the understanding that not all particle types will have the same cohesive properties. This multiple solid-phase model is a refinement of the classical DEM model that represents the particle physics more realistically, especially for heterogeneous systems. A preliminary parametric study is carried out considering varying cohesive properties and volume fractions for the different solid phases.

In this paper, according to the migration and diffusion law of MICP solution in fracture-pore medium, the migration and diffusion equation of MICP solution in loess fracture-pore medium was derived first. Then, the migration and diffusion test was carried out by using the self-made Mdevice. In the model, the apertures of the fracture of 0.5 mm, 1.0 mm and 1.5 mm were selected, and the calcium ion concentrations at different points were measured by atomic absorption method, to obtain the distribution map of calcium ion concentration. According to the test results, the migration speed of calcium ions in the direction along the fracture is less than the diffusion speed of the wet peak, and the vertical fracture direction is faster than the diffusion speed of the wet peak. The distribution range of calcium ion concentration increases first and then decreases with the increase in fracture opening. COMSOL was used to compile the mathematical equation, and the whole process of MICP solution migration and diffusion was numerically simulated. The numerical calculation results are basically consistent with the experimental results, and the derived mathematical equation is reasonable.

Enzyme induced carbonate precipitation (EICP) is a promising technique in the field of biocementation due to its efficiency and controllability. Although many studies have proved its reliability in different environment, little attention has been paid to the influence of humic substances on the EICP. Humic substances cover most of the surface soil across the world land with vegetation, which varies according to the density of vegetation and climate. To understand the compatibility of this technique to distinct problematic soils, it is important to figure out how humic substances could affect the carbonate precipitation process induced by urease enzyme. Therefore, this study aims to investigate the effects of humic acid (HA), one type of humic substance, on the soil solidification through EICP. For this purpose, HA was added to natural soil with varying addition amounts (0%, 1%, 2%, 4%, 8%, 16%) in soil column solidification tests. The results found that the cementation effectiveness was enhanced by a small amount of HA addition (<4%), while an addition up to 8% greatly inhibited the formation of calcium carbonate. At the same time, soil samples were buffered by HA in a weak acidic condition, thus preventing the emission of undesirable by-product ammonia in the ureolysis process. Therefore, this study makes a contribution to research on enzymatic biocementation by demonstrating the effects of HA on the cementation effectiveness of EICP technique.

Bio-mediated soil improvement methods keep on gaining the attention of geotechnical engineers and researchers globally due to their nature-based elegance and eco-friendliness. Most prevalent bio-mediated soil improvement methods include microbially induced carbonate precipitation (MICP) and enzyme-induced carbonate precipitation (EICP). During their processes, the bacteria/free urease hydrolyzes the urea into ammonium and carbonic acid, which is accompanied by a considerable increase of alkalinity (about pH 9.0). The major problem associated with the above techniques is the release of gaseous ammonia that is extremely detrimental. Therefore, this study aims to propose a new sustainable approach involving lactic acid bacteria to facilitate the calcium phosphate mineralization for the strengthening of sand matrix. The major objectives of this investigation are: (i) to evaluate the urease activity of the lactic acid bacteria under different temperatures, pH conditions and additions of metal ions, (ii) to assess the treated sand matrix, (iii) to perform cost analysis. The outcomes indicated that Limosilactobacillus sp. could effectively facilitate the urea hydrolysis, hence increasing the pH from acidic to neutral and providing a desirable environment for the calcium phosphate to mineralize within the voids of the sand. The addition of 0.01 % Ni²⁺ in culture media was found to enhance the urease activity by 38.8 % and compressive strength over 40 %. A combined formation of amorphous- and whisker-like precipitates could bridge a larger area at particle-particle contact points, thereby faciliating a strong force-network in sand matrix. The mineralized calcium phosphate compound was found to be brushite. The cost herein for producing 1 L treatment solution was estimated to be about 2.5-folds and 11.8-folds lower compared to that of MICP and EICP treatment solutions, respectively. Moreover, since the treatment pH could potentially be regulated between acidic-neural range, it would greatly control the release of gaseous ammonia. With several environmental and economical benefits, the study has disclosed a new sustainable direction for sand improvement via the use of lactic acid bacteria.

The antlions dig a conical simple pit in sand to catch ants. The funnel shape of the trap is deliberate with a critical angle of repose and is steep and shallow enough to trigger avalanches and cause struggling prey to fall into the funnel. The trap should be designed by optimizing pit morphology according to natural selection. In the current study, antlion behavior and pit morphology in the sand samples with different particle shapes and particle size distributions were studied. The small larvae build in fine sand and silty sand, while larger ones prefer fine to medium sands. However, there is no preference for sands with different particle shapes. Further, the static and dynamic angles of repose for the sand samples were measured, and the slope of the pits was compared with the repose angles. The angle of the heap slope oscillated between an upper angle or angle of sliding (the angle that triggers a landslide) and a lower angle named repose angle.

This study presents a sustainable approach to soil improvement by integrating polyvinyl alcohol (PVA) into the Soybean Crude Urease Carbonate Precipitation (SCU-CP) technique. The research aims to enhance SCU-CP, which utilizes soybean-derived urease to precipitate calcium carbonate, bonding soil particles and increasing strength. Challenges such as low solution viscosity and inconsistent carbonate precipitation are addressed by incorporating PVA, a biodegradable polymer that improves viscosity and retention. Comprehensive evaluations reveal significant findings: increasing PVA concentration enhances solution viscosity and results in higher calcium carbonate precipitation. Water retention assessments show that the PCP-1% treatment increases saturation water content (w_s) to 0.263 compared to 0.217 for untreated soil, while also reduces the air-entry value (α). Unconfined Compressive Strength (UCS) tests indicate substantial improvement for PCP-1%, achieving approximately 140 kPa, with values reaching 179 kPa after 28 days. Calcium carbonate content measurements reveal that SCU-CP exhibits a variable distribution (standard deviation of 1.13), while PCP-1% demonstrates a more uniform distribution (standard deviation of 0.60), indicating improved effectiveness. Durability assessments through wet-dry cycling show that SCU-CP experiences a mass loss of 36.5%, while PCP-1% retains only 5% mass loss and maintains a UCS values. SEM images indicate that SCU-CP forms spherical structures, whereas PCP-1% produces a more diverse and crystalline morphology, suggesting better nucleation and distribution. Overall, the polymer-assisted SCU-CP technique (PCP) demonstrates significant potential for effective soil improvement.

As lunar exploration develops, lunar construction is increasingly prominent and the in-situ lunar regolith molding becomes a technical challenge. This study proposes a lunar regolith molding technology based on biocarbonated magnesium oxide (MgO) with urea pre-hydrolyzed, which has the potential to achieve an unconfined compressive strength (UCS) of approximately 10 MPa after 24 h of curing. The study investigates the physical and mechanical properties of biocarbonated lunar regolith samples with varying urea concentrations, bacterial concentrations, and MgO contents. Scanning electron microscopy (SEM) was employed to examine the microstructural properties of the samples. The results demonstrated that the maximum UCS and E₅₀ were achieved at a urea concentration of 1.0 mol/L, a bacterial concentration of 1.0, and a MgO content of 15%. However, the carbonate content test indicated that the highest urea efficiency was observed at 10% MgO. Microscopic images show that the produced hydromagnesite is the most structured at the urea concentrations of 1.0 mol/L and 2.0 mol/L, corresponding well with the strength performance of the specimens. The pre-hydrolysis method can promote the efficiency of biocarbonated magnesium oxide but it highly depends on the concentration of the produced carbonate. Conclusively, the findings of this study offer a promising avenue for lunar regolith molding.

In this study, we demonstrate that diatoms, through their bioweathering process, can enhance the properties of lunar soil, thereby facilitating the cultivation of crops. Detailedly, diatoms can deconstruct lunar soil minerals to polish the sharp edge of the minerals and release nutrients, and aggregate lunar soil particles for water retention. In addition, diatoms possess a high degree of resilience to space conditions, with the capacity to consume carbon dioxide and release oxygen. Furthermore, they have been observed to utilize human waste as a source of sustenance, thus rendering them a promising candidate for the in situ modification of lunar soil. This study offers valuable insights into the potential for diatoms to contribute to future space habitation and exploration.