Biogeotechnics最新文献

Microbially induced carbonate precipitation (MICP) catalyzed by S. pasteurii has attracted considerable attention as a bio-cement that can both strengthen and seal geomaterials. We investigate the stress sensitivity of permeability reduction for the initially high-permeability Berea sandstone (initial permeability ∼110 mD) under various durations of MICP-grouting treatment. The results indicate that after 2, 4, 6, 8 and 10 cycles of MICP-grouting, the permeabilities decrease incrementally by 87.9%, 60.9%, 38.8%, 17.3%, and then 5.4% compared to the pre-grouting condition. With increasing the duration of MICP-grouting, the sensitivity of permeability to changes in stress gradually decreases and becomes less hysteretic. This stress sensitivity of permeability is well represented by a power-law relationship with the coefficients representing three contrasting phases: an initial slow reduction, followed by a rapid drop, culminating in an asymptotic response. This variation behavior is closely related to the movement and dislocation of the quartz framework, which is controlled by the intergranular bio-cementation strength. Imaging by scanning electron microscopy (SEM) reveals the evolution of the stress sensitivity to permeability associated with the evolving microstructures after MICP-grouting. The initial precipitates of CaCO₃ are dispersed on the surfaces of the quartz framework and occupy the pore space, which is initially limited in controlling and reducing the displacement between particles. As the precipitates continuously accumulate, the intergranular slot-shaped pore spaces are initially bonded by bio-CaCO₃, with the bonding strength progressively enhanced with the expanding volume of bio-cementation. At this stage, the intergranular movement and dislocation caused by compaction are reduced, and the stress sensitivity of the permeability is significantly reduced. As these slot-shaped pore spaces are progressively filled by the bio-cement, the movement and dislocation caused by compaction become negligible and thus the stress sensitivity of permeability is minimized.

The sand-dust weather has become an environmental hazard in the world. However, it is still a challenge to control sandstorms and decrease sand-dust weather. The biomineralization technology for solidifying desert sands has been developed as a novel method in recent years. In this study, the wind erosion tests and verification tests of the sand solidification system were conducted via a series of laboratory experiments. The effects of sand barriers, injecting volume and concentration of the biochemical solution in the sandstorm protection were studied. Moreover, a field test of 60,000 square metres was conducted in the solidification area on both sides of the Wuma Highway in the Tengri Desert. The biomineralization technique was used to solidify sand to prevent the wind from blowing quicksand onto the newly built highway and causing accidents. Results demonstrated that the biomineralization sand solidification method had a good solidification ==effect, improved the survival rate, and promoted the growth of plants in the desert. This innovative biomineralization technology is an environmentally responsible technology to control sandstorm disasters.

Rainfall-induced landslides, exacerbated by climate change, require urgent attention to identify vulnerable regions and propose effective risk mitigation measures. Extensive research underscores the significant impact of vegetation on soil properties and slope stability, emphasizing the necessity to incorporate vegetation effects into regional landslide susceptibility mapping. This review thoroughly examines research integrating vegetation into landslide susceptibility mapping, encompassing qualitative, semi-quantitative, and quantitative forecasting methods. It highlights the importance of incorporating vegetation aspects into these methods for comprehensive and accurate landslide susceptibility assessment. This review explores the diverse roles of vegetation in slope stability, covering both aggregated impacts and individual influences, including mechanical and hydrological effects on soil properties, as well as the implications of evapotranspiration and rainwater interception on slope stability. While aggregated roles are integrated into non-deterministic methods as input layers, individual roles are considered in deterministic methods. In the application of deterministic methods, it is noteworthy that a considerable number of studies primarily concentrate on the mechanical impact, particularly the reinforcement provided by root cohesion. The review also explores limitations and highlights future research prospects. In the context of mapping landslide susceptibility amid changing climatic conditions, data-driven techniques encounter challenges, while deterministic methods present their advantages. Stressing the significance of hydrological impacts, the paper recommends incorporating vegetation influences on unsaturated soil properties, including the soil water characteristic curve and soil permeability, along with pre-wetting suction due to evapotranspiration and potential rainwater interception.

Soil desertification and salinization are the main environmental disasters in arid and semi-arid areas. It is of great significance to study the water - salt migration law of saline soil and propose corresponding water- salt regulation and control measures. Microbial-induced calcite precipitation (MICP) technology was proposed to improve saline soil based on salt inhibition, and the water–salt–heat coupling migration law and salt-frost heave deformation law of saline soil before and after improvement were studied using soil column model tests. XR1#, XR2#（Saline-alkali-tolerant mineralization bacteria isolated from saline soil) and Sporosarcina pasteurii were used in the MICP improvement and the effect of XR1# was the best. Under high-temperature evaporation, the water migration change rate, water loss rate, accumulated evaporation amount, and accumulated salt content of the improved soil columns within a depth range of 0–40 cm were reduced by an average of 53.6 %, 47.3 %, 69.5 %, and 40 %, respectively, compared with the untreated soil column. During low-temperature cooling, the characteristics of water-salt migration changed significantly, and the deformation of salt-frost heave decreased significantly. The water-salt content at the freezing point (−4.5 °C) changed from a cliff-like steep drop (untreated saline soil) to a slow decrease at environmental temperature (MICP-treated saline soil), and the amount of water crystallization decreased from 81 % to 56.7 % at −5 °C. At the end of the cooling process, the amount of salt-frost heaving on the surface of the soil columns decreased by an average of 62.7 %. Based on the measured data, a numerical simulation was conducted using the HYDRUS-1D model, which had good reliability and accurately simulated and predicted the law of water-salt migration in saline soil under the conditions of microbial solidification and improvement. MICP technology significantly reduced the change rate of water-salt migration and water evaporation in saline soil, hindered salt accumulation, and reduced salt-frost heave deformation, which effectively improved saline soil. The research results provide an important innovation and theoretical basis for the improvement of saline soil.

A close relationship exists between the pore network structure of microbial solidified soil and its macroscopic mechanical properties. The microbial solidified engineering residue and sand were scanned by computed tomography (CT), and a three-dimensional model of the sample was established by digital image processing. A spatial pore network ball-stick model of the representative elementary volume (REV) was established, and the REV parameters of the sample were calculated. The pore radius, throat radius, pore coordination number, and throat length were normally distributed. The soil particle size was larger after solidification. The calcium carbonate content of the microbial solidified engineering residue’s consolidated layer decreased with the soil depth, the porosity increased, the pore and throat network developed, and the ultimate structure was relatively stable. The calcium carbonate content of the microbial solidified sand’s consolidated layer decreased and increased with the soil depth. The content reached the maximum, the hardness of the consolidated layer was the highest, and the development of the pore and throat network was optimum at a depth of 10–15 mm.

This study explores the effects of two nucleating agents, sucrose and sorbitol, on soybean-urease induced calcium carbonate precipitation (SICP) at a crystal level. Comparative studies on the mineral composition, crystal size, surface morphologies and thermal stability of SICP samples with/without nucleating agent were investigated with high resolution XRD, SEM and synchronous thermal analyzer (STA), respectively. The results show the introductions of sorbitol or sucrose to SICP reduce the content of vaterite(114) from 10.07% to 1.81%–3.93%, indicating their effect on transforming vaterite into stabler calcite. Sorbitol can enlarge the crystals and improve the thermostability of SICP, indicating an improvement of the crystallinity of SICP. The sucrose-regulated SICP shows medium thermostability which is worse than SICP without the nucleating agent, indicating the addition of sucrose reduces the crystallinity of SICP. Sorbitol is an effective nucleating agent that can improve the behaviors all-around, while sucrose increases the calcite content of SICP but inhibits the crystallinity of SICP. This study reveals the regulations of SICP because of the introduction of sorbitol or sucrose, and provides guidance to the subsequent engineering application of SICP.

Biocarbonation of reactive magnesia based on microbially induced carbonate precipitation (MICP) process is a sustainable geotechnical reinforcement technology for strength development and permeability reduction. This method can be used to produce microbial restoration mortar (MRM) for the application of stone cultural relics restoration. In this paper, the influence of particle size distribution on the strength and porosity of MRM was examined. By mixing fine and coarse sandstone powder in various proportions, nine different particle size distributions were obtained to investigate the restoration performance, including the unconfined compressive strength (UCS), porosity, and color difference. The results indicate that the well-graded particle size distribution can lead to the UCS improvement and porosity reduction of MRM. The findings also imply that adding fine sandstone powder to the coarse sandstone powder can provide extra bridging contacts within the soil matrix. These bridging contacts can be easily connected by the precipitated hydrated magnesium carbonates (HMCs) minerals, consequently resulting in more effective bonding and filling within the pore matrix. The microstructural images of MRM confirm the formation of HMCs, which exhibited a dense network structure, filling out the gap and bonding the sandstone powders. Furthermore, the microbial restoration mortar showed a high weather resistance to dry-wet cycles, acid rain, and salt attack, which is attributed to better stability and strength of HMCs than the original calcic cemented minerals in sandstone.

The majority of cities worldwide are grappling with the challenge of dust pollution. Recently, the application potential of enzymatically induced carbonate precipitation (EICP), a novel environmentally friendly method, for dust control has been convincingly demonstrated. However, the long-term durability of EICP treatment is consistently a significant concern, particularly in regions prone to recurrent erosion caused by rainfall. As a result, the erosion durability of the EICP-treated dust soils requires further investigation. To address this, Polyacrylic acid (PAA) was added to the cementation solution in this study as the combined PAA and EICP treatment for dust control. The results showed that the addition of PAA slightly affected urea degradation; however, the combined PAA and EICP treatment significantly improved surface strength from 300 kPa to 500 kPa, especially for the wind-erosion resistance compared with the EICP treatment alone. The surface strength of samples treated with the combined PAA and EICP still exhibited a decrease due to repeated rainfall erosion, along with a reduction in calcium carbonate (CaCO₃) contents. Nevertheless, the decreasing slopes of surface strength (k = 13.434, 14.002, or 14.186) in response to repeated rainfall for EICP-PAA-treated slopes were much smaller than those for EICP-treated samples (k = 14.271), as well as the decreasing slopes of CaCO₃ contents, which suggested the slopes with the combined treatment had significantly improved durability. By comparing the cementation effect and the influence of repeated rainfalls on treated dust samples, the EICP-PAA (50 g/L) treatment achieved better dust control effects. Overall, the combined treatment of EICP-PAA shows promising potential for effectively suppressing dust generation and enhancing erosion durability.

The effects of desiccation cracking in clay soils on geotechnical constructions are substantial. This study investigates the viability of utilizing Enzyme-induced calcite precipitation (EICP), a bio inspired approach, as a potential solution for addressing desiccation cracking in fine-grain soils. For the EICP technique, crude soybean extract is employed for the purpose of urea hydrolysis. Multiple fluid samples, including a control sample, a cementation solution containing 1 M urea, 0.675 M CaCl₂, and 4 g/L milk, along with various concentrations of enzyme solutions (3–80 g/L), were tested for the study. To evaluate the surface cracking patterns, the method involved constant monitoring and photo recording using a high-resolution camera aided by image processing software. The results showed that fine-grain soils improved from increased calcite precipitation and decreased desiccation cracking intensity when the EICP method was used. Cementation and enzyme solution with low concentrations (3 g/L and 10 g/L) had similar effects on crack remediation, suggesting a modest influence. In contrast to the sample treated with water, the crack network remained unaltered in this case. CaCO₃ precipitation within the void area kept the crack network in place even as the void thickness decreased at increasing enzyme concentrations (30 g/L, 50 g/L, and 80 g/L). Wetting and drying cycles were found to decrease the crack ratio, crack width, and crack length in the EICP-treated sample, particularly under higher concentrations of urease enzyme. Lower enzyme concentrations of 3 g/L and 10 g/L have minimal impact on crack remediation but effectively inhibit new crack formation. Furthermore, higher enzyme concentrations result in calcium carbonate precipitates, forming a soil crust and increasing surface roughness. The study aims to enhance understanding of the EICP methodology and to provide novel perspectives on potential uses for soil enhancement.