The mineralization process of microbial-induced calcium carbonate precipitation (MICP) is influenced by many factors, and the uniformity of the calcium carbonate precipitation has become the main focus and challenge for MICP technology. In this study, the uniformity of the saturated calcareous sand treated with MICP was investigated through one-dimensional calcareous sand column tests and model tests. The coefficient of variation was employed in one-dimensional sand column tests to investigate the impact of injection rate, cementation solution concentration, and number of injection cycles on the uniformity of the MICP treatment. Additionally, model tests were conducted to investigate the impact of injection pressure and methods on the treatment range and uniformity under three-dimensional seepage conditions. Test results demonstrate that the reinforcement strength and uniformity are significantly influenced by the injection rate of the cementation solution, with a rate of 3 mL/min, yielding a favorable treatment effect. Excessive concentration of the cementation solution can lead to significant non-uniformity and a reduction in the compressive strength of MICP-treated samples. Conversely, excessively low concentrations may result in decreased bonding efficiency. Among the four considered concentrations, 0.5 mol/L and 1 mol/L exhibit superior reinforcing effects. The morphological development of calcareous sandy foundation reinforcement is associated with the spatial distribution pattern of the bacterial solution, exhibiting a relatively larger reinforcement area in proximity to the lower region of the model and a gradually decreasing range towards the upper part. Under three-dimensional seepage conditions, in addition to the non-uniform radial cementation along the injection pipe, there is also vertical heterogeneity of cementation along the length of the injection pipe due to gravitational effects, resulting in preferential deposition of calcium carbonate at the lower section. The application of injection pressure and a double-pipe circulation injection method can mitigate the accumulation of bacterial solution and cementation solution at the bottom, thereby improving the reinforcement range and uniformity.

Microbial-Induced Carbonate Precipitation (MICP) is an emerging, environmental-friendly, and sustainable technology that has shown great potential for soil stabilization. However, its process efficiency has been recognized as a major challenge for its practical application in engineering. Non-fat powdered milk (NFPM) has been shown to have positive effects in enzymatical-induced carbonate precipitation (EICP), so in this study, we evaluated its use as an additive in the MICP process. A comparison between conventional MICP and NFPM-modified MICP was conducted, including chemical conversion efficiency, urea hydrolysis rate, and mechanical performance of sandy soils. A series of laboratory tests including precipitation analysis, unconfined compressive strength (UCS), and microstructure analysis were conducted. The results showed that the addition of NFPM could improve urease activity, enhance chemical conversion efficiency, and lead to superior strength improvement compared to conventional MICP. Microstructure and particle size analysis revealed that the presence of NFPM was beneficial for larger crystal cluster formation between sand grains, which could result in stronger bonds and better mechanical performance. In summary, this study indicates that the use of NFPM in MICP process can represent a more sustainable and economically viable approach for soil stabilization. The findings provide valuable information for engineers and researchers working in soil stabilization and environmental engineering, highlighting the potential of using natural additives such as NFPM to promote the sustainable development of MICP technique.

The biocemented coral sand pile composite foundation represents an innovative foundation improvement technology, utilizing Microbially Induced Carbonate Precipitation (MICP) to consolidate a specific volume of coral sand within the foundation into piles with defined strength, thereby enabling them to collaboratively bear external loads with the surrounding unconsolidated coral sand. In this study, a series of shaking table model tests were conducted to explore the dynamic response of the biocemented coral sand pile composite foundation under varying seismic wave types and peak accelerations. The surface macroscopic phenomena, excess pore water pressure ratio, acceleration response, and vertical settlement were measured and analysed in detail. Test results show that seismic wave types play a decisive role in the macroscopic surface phenomena and the response of the excess pore water pressure ratio. The cumulative settlement of the upper structure under the action of Taft waves was about 1.5 times that of El Centro waves and Kobe waves. The most pronounced liquefaction phenomena were recorded under the Taft wave, followed by the El Centro wave, and subsequently the Kobe wave. An observed positive correlation was established between the liquefaction phenomenon and the Aristotelian intensity of the seismic waves. However, variations in seismic wave types exerted minimal influence on the acceleration amplification factor of the coral sand foundation. Analysis of the acceleration amplification factor revealed a triphasic pattern—initially increasing, subsequently decreasing, and finally increasing again—as burial depth increased, in relation to the peak value of the input acceleration. This study confirms that the biocemented coral sand pile composite foundation can effectively enhance the liquefaction resistance of coral sand foundations.

Pleurotus ostreatus, a saprotrophic fungus, has been proposed for the remediation of organic contaminants in soils and more recently for modifying the hydraulic and mechanical behaviour of granular soils. The in situ performance of fungal-based biotechnologies will be controlled by the fungal growth and associated biochemical activity that can be achieved in soil. In this study, the influence of environmental conditions (temperature, degree of saturation), substrate type (lignocellulose and spent coffee grounds) and concentration on the mycelium growth of P. ostreatus in sand are investigated. Furthermore, the evolution of growth/survival indicators (respiration, ergosterol concentration) and enzymatic activity (laccase, manganese peroxidase) are investigated. Temperature was shown to have a strong influence on the growth of P.ostreatus in sand: growth was observed to be delayed at low temperatures (e.g. 5 °C), whereas growth was prevented at high temperatures (e.g. 35 °C). No growth was observed at very low degrees of saturation (S_r=0% and 1.2%), indicating there is a critical water content required to support P.ostreatus growth. Within the mid-range of water contents tested radially, growth of P.ostreatus was similar. However, growth under saturated soil conditions was restricted to the air-water atmosphere due to the requirement for oxygen availability. Low substrate concentrations (1%-5%) resulted in high radial growth of P.ostreatus, whereas increasing substrate content further acted to reduce radial growth, but visual observations indicated that fungal biomass density increased. These results are important for understanding the feasibility of P.ostreatus growth under specific site conditions and for the design of successful treatment strategies.

Characterizing the architecture of tree root systems is essential to advance the development of root-inspired anchorage in engineered systems. This study explores the structural root architectures of orchard trees to understand the interplays between the mechanical behavior of roots and the root architecture. Full three-dimensional (3D) models of natural tree root systems, Lovell, Marianna, and Myrobalan, that were extracted from the ground by vertical pullout are reconstructed through photogrammetry and later skeletonized as nodes and root branch segments. Combined analyses of the full 3D models and skeletonized models enable a detailed examination of basic bulk properties and quantification of architectural parameters. While the root segments are divided into three categories, trunk root, main lateral root, and remaining roots, the patterns in branching and diameter distributions show significant differences between the trunk and main laterals versus the remaining lateral roots. In general, the branching angle decreases over the sequence of bifurcations. The main lateral roots near the trunk show significant spreading while the lateral roots near the ends grow roughly parallel to the parent root. For branch length, the roots bifurcate more frequently near the trunk and later they grow longer. Local thickness analysis confirms that the root diameter decays at a higher rate near the trunk than in the remaining lateral roots, while the total cross-sectional area across a bifurcation node remains mostly conserved. The histograms of branc;/.hing angle, and branch length and thickness gradient can be described using lognormal and exponential distributions, respectively. This unique study presents data to characterize mechanically important structural roots, which may help link root architecture to the mechanical behaviors of root structures.

Eco-geotechnical engineering plays a pivotal role in enhancing global sustainability and upholding the performance of earthen structures. The utilization of vegetation to stabilise geotechnical infrastructures is widely recognized and embraced for its environmentally friendly attributes. The spectre of climate change further intensifies the focus on the effects of temperature and humidity on vegetated soil. Consequently, there is a pressing need for research exploring the influence of changing climates on vegetated infrastructures. Such research demands a holistic and interdisciplinary approach, bridging fields such as soil mechanics, botany, and atmospheric science. This review underscores key facets crucial to vegetated geotechnical infrastructures, encompassing climate projections, centrifuge modelling, field monitoring, and numerical methodologies.

Natural cemented calcareous sand and limestone are highly complex and not well understood in terms of the mechanical behavior due to the difficulty of obtaining undisturbed samples from far sea. This paper proposes an artificial method in a laboratory setting using microbial-induced carbonate precipitation (MICP) to simulate the natural process of cementation of limestone. The artificially cemented sand has a high degree of similarity with the natural weakly limestone in three aspects: (1) the mineral composition of the cemented material is also granular calcite and acicular aragonite; (2) the microstructure in interconnected open pore network can be gradually closed and contracted with cementation. The porosity reaches to approximately 9.2%; (3) both the stress-strain relationship and the unconfined strength closely resemble that of natural weakly limestone. Furthermore, both static and dynamic behaviors of artificial limestone were studied by quasi-static compression tests and Split Hopkinson Pressure Bar (SHPB) tests, finding that the unconfined strength of weakly artifical limestone exponentially increases with increasing strain rate. A rate-dependent bond strength was proposed and implemented in software to reveal the mechanism of strain rate effects. It is found that the loading velocity is too high to keep in sync with the initiation and propagation of cracks under impact loading. This delay-induced viscosity may restrict the movement of the surrounding balls, thus increasing resistance.

Characterization of vegetation effect on soil response is essential for comprehending site-specific hydrological processes. Traditional research often relies on sensors or remote sensing data to examine the hydrological properties of vegetation zones, yet these methods are limited by either measurement sparsity or spatial inaccuracy. Therefore, this paper is the first to propose a data-driven approach that incorporates high-temporal-resolution electrical resistivity tomography (ERT) to quantify soil hydrological response. Time-lapse ERT is deployed on a vegetated slope site in Foshan, China, during a discontinuous rainfall induced by Typhoon Haikui. A total of 97 ERT measurements were collected with an average time interval of 2.7 hours. The Gaussian Mixture Model (GMM) is applied to quantify the level of response and objectively classify impact zones based on features extracted directly from the ERT data. The resistivity-moisture content correlation is established based on on-site sensor data to characterize infiltration and evapotranspiration across wet-dry conditions. The findings are compared with the Normalized Difference Vegetation Index (NDVI), a common indicator for vegetation quantification, to reveal potential spatial errors in remote sensing data. In addition, this study provides discussions on the potential applications and future directions. This paper showcases significant spatio-temporal advantages over existing studies, providing a more detailed and accurate characterization of superficial soil hydrological response.