Biogeotechnics最新文献

Utilizing Enzyme-Induced Calcium Carbonate Precipitation (EICP) reinforcement technology has emerged as an innovative approach for soil improvement. In this study, kitchen waste eggshell powder was used as an additive material for EICP. The high external surface area and affinity for calcium ions of eggshell powder, which render it a suitable nucleation site for calcium carbonate precipitation. Experimental results demonstrate that the incorporation of eggshell powder, by increasing the number of nucleation sites and promoting calcium carbonate precipitation, reduces the inhibition of enzyme products, modulates the precipitation pattern of calcium carbonate, improves particle size distribution, and consequently significantly enhances the unconfined compressive strength of the samples. Furthermore, a neutral pH is achieved within the reaction system without the addition of any acid, thus preventing significant ammonia emissions. This underscores the potential of kitchen waste eggshells for recycling in biocement applications.

In this review, the development and application of microbially induced carbonate precipitation (MICP) technology for the sealing of underground engineering fractures are discussed in detail. The importance of sealing micro-fractures in an environmentally friendly and efficient manner is emphasized, and the potential of the MICP method in controlling pore and fracture seepage is highlighted. The fundamental mechanisms, key influencing factors, numerical models, and applications of the MICP in the fields of geological CO₂ storage and oil resources development are comprehensively summarized in the paper. At the same time, the limitations of the existing research and the future research directions are discussed, especially in terms of improving the processing efficiency, environmental impacts, and cost considerations. Overall, the development of MICP technology provides a new environmentally friendly reinforcement method for geotechnical engineering and is expected to play a key role in the future development of underground space engineering.

Loose tailings are susceptible to static liquefaction during which they lose a substantial amount of their strength. This study examines a sustainable technique known as Microbially-Induced Calcite Precipitation (MICP) to improve the static liquefaction resistance of gold mine silty sand tailings. These materials were enriched with Sporosarcina pasteurii, consolidated in a direct simple shearing apparatus, and subjected to several injections of a cementation solution. Calcified tailings were then sheared under constant-volume and constant vertical stress conditions to evaluate their undrained and drained shearing behaviors. Results showed that bio-mineralization can prevent the occurrence of static liquefaction in tailings by reducing their contraction tendency. This is demonstrated by the strong strain-hardening behaviors of the treated tailings specimens compared to the strain-softening and undrained strength loss in specimens of the untreated tailings. Substantial increases in the tailings undrained and drained shear strengths (by up to 30 - 50 kPa), improvements (by up to 5 MPa) in their tangent moduli, and more than 5° rise in their friction angles are observed in the direct simple shear tests following MICP-treatment. The critical state line of tailings is also found to be steeper and shifted to denser void ratios following MICP treatment. These changes reduce liquefaction susceptibility of tailings and enhance their resistance against static liquefaction. Post-treatment acid dissolution further indicates that CaCO₃ contents of about 4% to 11% precipitated in the treated specimens. This amount decreases with increasing specimens void ratio. Changes in the microstructural fabric of the cemented tailings particles are also characterized using scanning electron microscopic (SEM) images and X-ray diffraction (XRD) analyses.

Biochar has emerged as a promising soil amendment for improving soil structure. Yet, its impact on rainfall-induced soil erosion varies across individual studies. To address this gap, we conducted a statistical meta-analysis of 174 paired comparisons from 45 published studies to integratedly evaluate the impacts of biochar on rainfall-induced soil erosion through biochar and soil properties, as well as experimental conditions. Overall, biochar significantly reduced soil erosion by 27.86%. The response ratio (lnRR) of biochar-induced soil erosion exhibited significant variability across different subgroups. Concerning biochar properties, a more favorable influence was observed in other sources biochar (e.g., manure and sewage sludge biochar) compared to wood based and crop waste biochar, and those produced at lower pyrolysis temperatures (< 500 °C). Increasing biochar dosage was not consistently effective. The optimal range was 0.8%–2%, resulting in a 36.07% reduction in soil erosion. Regarding the soil properties, a higher sand/clay ratio of soil significantly enhanced the performance of biochar (p < 0.0001). Specifically, an insignificant effect was observed in fine-grained soils, whereas the highest reduction of 52.97% was noted in coarse-grained soils. Moreover, long-term field experiments induced greater reductions in soil erosion with biochar (35.30%) compared to short-term laboratory studies (29.62% and 12.59%). This meta-analysis demonstrates that biochar, as a potential soil amendment, could effectively mitigate rainfall-induced soil erosion by considering a combination of soil properties along with specific biochar properties.

A new landfill cover system, biochar-methanotrophs-clay (BMC) cover is recommended for reducing methane emissions at landfills. It also contributes to decreasing soil permeability and improving soil water retention in a long time, due to highly porous structure of biochar and the growth metabolism of methanotrophs. To determine the effects of biochar content, oxidation aging times and methane-filled days on hydraulic properties, a total of 60 groups of experiments were conducted. The saturated hydraulic conductivity (k_sat) was obtained by flexible wall permeameter with controllable hydraulic head pressure. The results showed that the k_sat of BMC increased with increasing biochar content and oxidation aging times, while decreased with adding methane-filled days. The soil-water characteristic curves (SWCCs) were obtained with soil suction measured by the filter paper method. The results indicated the water retention capacity of MBC reduced with increasing oxidation aging times but increased with adding methane-filled days. Detected by mercury intrusion porosimetry (MIP), fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM), the differences displayed the changes of pore structures and extracellular polymeric substances (EPS). The oxidation aging of biochar increased the volume of pores, resulting in the increased k_sat and the decreased water retention capacity. However, the growing of methanotrophs decreased the volume of pores, resulting in the k_sat decreased and the water retention capacity increased due to EPS. No matter how many times the oxidation aging process was experienced, the BMC with longer methane-filled days exhibited relatively lower k_sat and better water retention capacity. This implied a more stable barrier capacity to reduce water infiltration in the long term. By combing a series of macro and micro experiments, this paper provides theoretical guidance for the application of biochar-methanotroph-clay mixture to landfill covers.

To fulfill the operational demands of deep-sea tracked mining vehicles traversing soft seabed substrates, an evaluation of the characteristics of these substrates was conducted, drawing a comparison with the land swamp black soil found in the buffalo's habitat. Employing the principles of biomimicry, two distinct types of bionic grouser were devised, replicating the configuration of the buffalo's hooves in both the horizontal and vertical planes. Utilizing self-constructed testing platforms, exhaustive examinations of the reinforcement efficacy of these bionic track grousers were undertaken, spanning from single-grouser to multi-grouser configurations and encompassing the entire track assembly. The findings unequivocally demonstrate a pronounced and consistent enhancement in traction force for both types of bionic grousers. Notably, the W-shaped bionic grouser, mimicking the horizontal contour of the buffalo's hoof, exhibits the most substantial increase in traction force. The maximum enhancement in traction force for individual bionic grouser exceeds 30%, while the overall track achieves an increase of over 19%. This research provides a valuable reference and establishes a foundational framework for the design of equipment tailored for the locomotion of deep-sea tracked mining vehicles across soft substrates.

Microbially or enzyme induced carbonate precipitation has emerged to be a new type of soil improvement method. However, it appears that the biocementation process is affected by many factors and a common understanding on the control factors on the biocement effect has not been reached. This paper attempts to identify the main factors that controlling the MICP or EICP effect through an in-depth discussion on the fundamentals of biocementation process. Similar to other cemented granular materials, biocemented soil is a structural soil composite consisting of soil skeleton and biocement force chain or biocement network. The strength and stiffness of the biocemented soil is controlled by the reinforcement effect of the biocement network on the soil skeleton or the interplay of the soil skeleton and precipitates. The contribution of the strength by soil skeleton is affected by the soil types and soil properties, while the contribution of the precipitates is through the distribution of the biocement network and the properties of the precipitates.