Biogeotechnics最新文献

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.

This study focuses on the development and testing of a bio-inspired self-burrowing dual anchor soft probe for potential geotechnical applications. Dual anchor refers to the form of movement in soils in which some bivalve molluscs adopted by alternately generating anchoring effects in the soil through shell expansion and fluid-filled feet. By mimicking this mechanism, this study used pneumatic artificial muscles as soft actuators and developed an autonomous burrowing probe. The structure and the performance of the actuators and the probe were investigated and optimized. The burrowing-out process of the dual anchor probe was not a simple upward movement. Instead, it rose in the inflation phase and slipped downward in the deflation phase. The difference between the two was a stride in one single step. In the sands with relative densities of 30%, 50%, and 80%, the total slips accounted for 18.8%, 19.6%, and 26.9% of the total upward movements, respectively. Thus, the entire movement process showed a reciprocating upward trend. The burrowing process could be divided into a restricted stage and a free stage according to whether shear failure occurs in the overlying soil layer. When the soil density was high, the initial stage of burrowing was in a restricted stage. The amount of rise and slip were at a low level and increased slowly as the number of cycles increased. When the burrowing process was in the free stage, the increase was basically stable at a high value and accompanied by small slips.

Detrimental impacts of dust caused by mine tailings have yielded to several studies on the efficiency of different soil stabilizers. Bacterial stabilization has been recognized as a reality within recent decades, where bacteria could get adhesion to the grains and stabilize the soil particles. However, these bacteria are prone to be destroyed while exposed to the normal environmental conditions. In this study, the effects of microcapsules containing two types of bacterial freeze-dried spores (B.Subtilis Natto LMG 19457 and B.ESH) have been investigated on the mine tailing stability in terms of two parts. The first part of the study is dedicated to the fabrication of microcapsules within the two bacteria and identification of the characteristics of these microcapsules to set the time of microcapsules break and release in the soil. The urea-formaldehyde microcapsules containing tung oil were synthesized using microencapsulation method and at the following, the bacterial spores of B.Subtilis Natto LMG 19457 and B.ESH which had the high durability and the capability to grow in the silicon oil, were added to the microcapsules. The microcapsules effect on MT specimens and the viability of encapsulated spores were determined. The characteristics of the capsules were analyzed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermo-gravimetric thermal analysis (TGA). In the second part, wind tunnel tests were conducted to study the effects of microorganism stabilizers on mine tailings. The results indicated that the dust erosion reduced from 16% - using water as a stabilizer- to the 0.2% while using microcapsules containing B.Subtilis Natto LMG 19457 and 0.8% while using microcapsules containing ESH. The results showed the high efficiency of microcapsules containing bacteria in stabilizing the MTs. This phenomenon was proved by SEM imaging in which the voids were bounded significantly while using the bacteria.

This study presents a new restoration method for fragmented ceramic cultural relics using bioslurry-induced biocementation via a microbially induced calcium carbonate precipitation (MICP) process. Bioslurry is highly urease active calcium carbonate crystals, which serve as filling and cementitious material with newly induced calcite precipitation when supplying cementation solution (urea and calcium source). With the pre-filling of bioslurry and newly induced calcite crystals, the fragmented ceramic can be connected and the gap along the fracture surface can be sealed. Due to the high urease active bacteria cells embedded in bioslurry, the ceramic restoration can be completed in 24 h with the optimal concentration of cementation solution of 1.6 M. Taking the advantage of bonding effect gained from newly induced calcite precipitation, the tensile strength was improved up to 0.92 MPa through a customized tensile strength test. This is satisfactory to ensure the stability and integrity of fragmented ceramic after bioslurry-induced restoration. A demonstrative restoration has been completed on fragmented ceramics from Ming Dynasty. With the good bonding strength and high stability of bioslurry-induced calcite precipitation, the proposed bioslurry-induced restoration method contributes valuable insights to the conservation of ceramic cultural relics. Other prospective applications include the restoration of masonry relics and bone relics.

Microbially Induced Carbonate Precipitation (MICP) presents a promising avenue for sustainable carbon management, offering a rapid alternative to natural carbonate formation. This paper explores the potential of MICP, particularly through ureolysis, in carbon storage and greenhouse gas mitigation. Urease-producing bacteria play a key role by converting CO₂ into calcium carbonate (CaCO₃). These microbes thrive in various environments, from soils to construction sites, making MICP a versatile tool for Carbon Capture and Storage (CCS). This process not only results in the formation of solid carbonates but also effectively sequesters CO₂, positioning MICP as a transformative approach for climate change mitigation. The article highlights MICP’s capacity to harness microbial activities for environmental benefits, emphasizing its importance in reducing atmospheric CO₂ levels and contributing to a more sustainable future.

Bio-cemented soils can exhibit various types of microstructure depending on the relative position of the carbonate crystals with respect to the host granular skeleton. Different microstructures can have different effects on the mechanical and hydraulic responses of the material, hence it is important to develop the capacity to model these microstructures. The discrete element method (DEM) is a powerful numerical method for studying the mechanical behaviour of granular materials considering grain-scale features. This paper presents a toolbox that can be used to generate 3D DEM samples of bio-cemented soils with specific microstructures. It provides the flexibility of modelling bio-cemented soils with precipitates in the form of contact cementing, grain bridging and coating, and combinations of these distribution patterns. The algorithm is described in detail in this paper, and the impact of the precipitated carbonates on the soil microstructure is evaluated. The results indicate that carbonates precipitated in different distribution patterns affect the soil microstructure differently, suggesting the importance of modelling the microstructure of bio-cemented soils.

Shallow landslides can be mitigated through the hydro-mechanical reinforcement provided by vegetation. Several critical parameters, such as plant spacing and plant age, play a significant role in influencing bioengineered slope stability facilitated by vegetation. However, the coupling of these effects on the stability of vegetated slope has been ignored. The objective of this study is to investigate the hydro-mechanical impact of vegetation growth and spacing on the stability of bioengineered slopes based on the predictions of a calibrated numerical model against field measurements. The impact of vegetation is investigated, with specific attention given to different plant spacing and growth stages, utilizing Schefflera arboricola. In the context of rainfall, it was observed that younger vegetation demonstrated more effective matric suction retention and recovery up to 25 kPa compared to the aged vegetation. Vegetation was revealed to substantially enhance the factor of safety up to 0.3 compared to the bare slope. Plant growth and reducing plant spacing increased the impact of root systems on both hydraulic and mechanical stability, primarily attributable to the influence of root cohesion rather than transpiration rates. The results revealed that the mechanical contribution to the factor of safety enhancement was raised from one-third to two-thirds because of the vegetation-induced cohesion within the growing rooted zone.