Biogeotechnics最新文献

Biocementation is an emerging field within geotechnical engineering that focuses on harnessing microbiological activity to enhance the mechanical properties and behavior of rocks. It often relies on microbial-induced carbonate precipitation (MICP) or enzyme-induced carbonate precipitation (EICP) which utilizes biomineralization by promoting the generation of calcium carbonate (CaCO₃) within the pores of geomaterials (rock and soil). However, there is still a lack of knowledge about the effect of porosity and bedding on biocementation in rocks from a mechanistic view. This experimental study investigated the impact of porosity and bedding orientations on the mechanical response of rocks due to biocementations, using two distinct biocementation strategies (MICP and EICP) and characteristically low porosity but interbedded rocks (shale) and more porous but non-bedded (dolostone) rocks. We first conducted biocementation treatments (MICP and EICP) of rock samples over a distinct period and temperature. Subsequently, the rock strength (uniaxial compressive strength, UCS) was measured. Finally, we analyzed the pre- and post-treatment changes in the rock samples to better understand the effect of MICP and EICP biocementations on the mechanical response of the rock samples. The results indicate that biocementations in dolostones can improve the rock mechanical integrity (EICP: +58% UCS; MICP: +25% UCS). In shales, biocementations can either slightly improve (EICP: +1% UCS) or weaken the rock mechanical integrity (MICP: −39% UCS). Further, results suggest that the major controlling mechanisms of biogeomechanical alterations due to MICP and EICP in rocks can be attributed to the inherent porosity, biocementation type, and bedding orientations, and in few cases the mechanisms can be swelling, osmotic suction, or pore pressurization. The findings in this study provide novel insights into the mechanical responses of rocks due to MICP and EICP biocementations.

The understanding of rainfall-induced landslides on gentle, loose-fill slopes is limited in comparison to steep slopes. Hence, two physical model tests were conducted on silty sand slopes under continuous rainfall: one on a bare slope and the other on a slope planted with ryegrass. The slope angle of 25° is much lower than the internal friction angle of slope material (34.3°), which makes the model test fall well into the category of gentle slope. For the initially unsaturated bare slope, a rainfall event with return period of 18 years could trigger a rapid and retrogressive global sliding, which differs from previous findings that gentle slopes would only experience shallow failure. A sudden increase in pore-water pressure was simultaneously observed, which might be generated by the wetting-induced collapse of unsaturated loose soil. On the other hand, the stability of the slope with grass plantation was significantly enhanced, and it was able to withstand rainfall event more severe than those with a return period of 100 years, with only minimal deformation. The results suggest that the gain in shear strength due to ryegrass roots surpasses the additional sliding force caused by the increased water retention capability. Additionally, it is found that the abrupt change in pore pressure was no longer indicative of slope failure in the case of the grass-reinforced slope.

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.

In order to study the infiltration characteristics of grassland soil in the super large scale landslides distribution area in the upper reaches of the Yellow River, this study selected the Xiazangtan super large scale distribution area in Jianzha County as the study area. Through experiments and numerical simulations, plant roots characteristics, soil physical properties and infiltration characteristics of naturally grazed grassland and enclosed grassland with different slope directions were compared and analyzed, and the influence of rainfall on seepage field and stability of the two grassland slopes were discussed. The results show that the highest soil moisture infiltration capacity (FIR) is found on the shady slope of the enclosed grassland (2.25), followed by the sunny slope of the enclosed grassland (1.23) and the shady slope of the naturally grazed grassland (−0.87). Correlation analysis show that soil water content, root dry weight density, total soil porosity, number of forks and root length are positively correlated with infiltration rate (P＜0.05), whereas soil dry density is negatively correlated with infiltration rate (P＜0.05). The results of stepwise regression analyses show that soil water content, total soil porosity, root length and number of forks are the main factors affecting soil infiltration capacity. And the ability of roots to increase soil infiltration by improving soil properties is higher than the effect of roots itself. After 60 min of simulated rainfall, the safety factors of the shady slopes of naturally grazed grassland and enclosed grassland are reduced by 29.56% and 19.63%, respectively, comparing to those before rainfall. Therefore, in this study, the roots play a crucial role in regulating soil infiltration and enhance slope stability by increasing soil water content, soil total porosity and shear strength while decreasing soil dry density. The results of this study provide theoretical evidence and practical guidance for the effective prevention and control of secondary geological disasters such as soil erosion and shallow landslide on the slope of river banks in the study area by using plant ecological measures.

Microbially induced calcium carbonate precipitation (MICP) is recognized as a promising technique for soil improvement. The morphological evolution of calcium carbonate (CaCO₃) crystals during the MICP process significantly impacts the engineering properties of biocemented soils. However, the morphological changes of CaCO₃ precipitates upon bacterial adsorption onto crystal surfaces have not been sufficiently studied. This study employs real-time laser scanning confocal microscopy (LSCM) to simultaneously monitor the dynamics of CaCO₃ growth and bacterial attachment during the MICP process, while fluorescence staining is used to differentiate between living and dead bacteria. The results indicate that during the initial stage of the MICP process, the predominant morphology of the CaCO₃ crystals was elliptical, with a minor fraction exhibiting a rhombohedral morphology. Over time, additional elliptical crystals gradually formed around the existing elliptical ones. As the crystals grew, certain bacteria in the vicinity of the crystals became adsorbed onto their surfaces, irrespective of bacterial viability. However, bacterial adsorption did not alter the morphology of the crystals. The study provides microscale insights into the mechanisms of bacterial attachment to CaCO₃ crystals during biomineralization.

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.