Biogeotechnics最新文献

Triaxial compression tests were conducted on the alfalfa root-loess complex at different growthperiods obtained through artificial planting. The research focused on analyzing the time variation law of the shear strength index and deformation index of the alfalfa root-loess complex under dry-wet cycles. Additionally, the time effect of the shear strength index of the alfalfa root-loess complex under dry-wet cycles was analyzed and its prediction model was proposed. The results show that the PG-DWC (dry-wet cycle caused by plant water management during plant growth period) causes the peak strength of plain soil to change in a "V" shape with the increase of growth period, and the peak strength of alfalfa root-loess complex is higher than that of plain soil at the same growth period. The deterioration of the peak strength of alfalfa root-loess complex in the same growth period is aggravated with the increase of drying and wetting cycles. Compared with the 0 days growth period, the effective cohesion of alfalfa root-loess complex under different dry-wet cycles maximum increase rate is at the 180 days, which are 33.88%, 46.05%, 30.12% and 216.02%, respectively. When the number of dry-wet cycles is constant, the effective cohesion of the alfalfa root-loess complex overall increases with the growth period. However, it gradually decreases comparedwith the previous growth period, and the minimum increase rate are all at the 180 days. For the same growth period, the effective cohesion of the alfalfa root-loess complex decreases with the increase of the number of dry-wet cycles. This indicates that EC-DWC (the dry-wet cycles caused by extreme natural conditions such as continuous rain) have a detrimental effect on the time effect of the shear strength of the alfalfa root-loess complex. Finally, based on the formula of total deterioration, a prediction model for the shear strength of the alfalfa root-loess complex under dry-wet cycles was proposed, which exhibits high prediction accuracy. The research results provide useful guidance for the understanding of mechanical behavior and structural damage evolution of root-soil composite.

The Yellow River sediment (YRS) is an important potential soil resource for the mine land reclamation and ecological restoration in the arid regions of northern China. However, it has the shortcomings of poor water-holding capacity and needs to be modified urgently. Therefore, two types of biochar, namely rice husk biochar (RHB) and coconut shell biochar (CSB), were utilized in this study to modify the YRS and compared with rice husk ash (RHA). Some engineering properties of the modified YRS (MYRS), including pore structure, water retention, permeability, and vegetation performance, were investigated by considering the effects of biochar types and dosages. Results showed that the addition of the three materials decreased the bulk density of the YRS and increased the volume of extremely micro pore (d<0.3 µm), as well as the effective porosity and capillary porosity, thus contributed to an increase in the water-holding capacity of the sediment. Among the three conditioners, RHB is optimal choice for improving the water-holding capacity of YRS. Furthermore, the effect becomes more pronounced with increasing application rates. With the addition of the three materials, the permeability coefficients of MYRS gradually decreased, while the water retention rate during evaporation significantly increased. The pot experiment showed that the three conditioners all had significant promoting effect on the growth of oats. In particular, compared to plain soil, the total biomass of oats grown for 21 days increased by 17.46%, 32.14%, and 49.60% after adding 2%, 4%, and 8% RHB, respectively. This study introduces a new approach for using YRS as planting soil in arid and semi-arid areas of China to facilitate mine ecological restoration.

In recent years, the development and construction of island reefs have been flourishing. Due to the remoteness of island reefs from the mainland, the scarcity of building materials, and the high transportation costs, it is imperative to use local marine resources, and the potential value and status of coral mud on island reefs, which is formed by the remains of corals and other biological entities, is becoming increasingly prominent. Utilization and optimization of natural resources on island reefs have become a brand-new research direction and challenge. This article mainly focuses on the development of a new type of green engineering material, coral mud, for use in building surface layers. Thickness effects, PVA fiber (vinylon staple fiber) modification, and HPMC (Hydroxypropyl Methyl Cellulose) adhesive modification are taken into consideration. Through laboratory tests and image processing technology, fractal theory, and electron microscopy experiments, the macro-meso-microscopic multi-scale cracking rules of the coral mud surface layer and the optimization modification rules of PVA fibers and HPMC adhesives are revealed. The results demonstrate that the performance of the coral mud surface layer is superior to that of the kaolin surface layer, and the 10 mm thickness performs better than the 5 mm and 20 mm thicknesses. As the thickness of the coral mud surface layer increases, the contact between coral mud particles becomes denser, the scale of surface micro-cracks decreases, and the number of micro-pores decreases. PVA fibers can effectively inhibit the further development of macro and micro cracks and play a good bridging role. There is a bonding and adhesion relationship between coral mud and PVA fibers, and they have a good synergistic effect in inhibiting macro and mesoscopic cracks. With the increase in HPMC adhesive content, the number of micro-cracks and the scale of micro-cracks decrease accordingly, and the structure and performance of the coral mud surface layer are further improved. Overall, PVA fibers are more effective than HPMC adhesives in inhibiting the cracking of the coral mud surface layer. This provides valuable guidance for the development and application of coral mud in wall surface materials.

The objective of this study is to explore how different layer thicknesses affect the desiccation cracking behaviour of vegetated soil. During the experiment, an electronic balance was employed to quantify water evaporation, while a digital camera was utilized to capture the initiation and progression of soil surface cracking. Results indicate that in the early drying process, the rate of evapotranspiration in vegetated soil correlates positively with leaf biomass. For soil samples with the same layer thickness, the constant rate stage duration is consistently shorter in vegetated soil samples than in their bare soil counterparts. As the layer thickness increases, both vegetated and bare soil samples crack at higher water content. However, vegetated soil samples crack at lower water content than their bare soil counterparts. Vegetation significantly reduces the soil surface crack ratio and improves the soil crack resistance. The crack reduction ratio is positively correlated with both root weight and length density. In thicker vegetated soil layers, the final surface crack length noticeably declines.

Ancient cultural relics built of red sandstone have high historical value. However, due to the acceleration of the industrialization process of human civilization, increasingly frequent acid rain has caused irreversible damage to the surface of red sandstone artifacts. In this research, a fluor-silane modified nano-calcium carbonate (CaCO₃) was prepared as a biomimetic hydrophobic coating for the conservation of red sandstone inspired by the lotus leaf effect. Characterizations and immersion tests were carried out to assess the protective properties of the coating. XRD, FT-IR, TEM and SEM were combined to characterize the morphology of the coating. In addition, the water contact angle was measured before and after immersion in the simulated acid rain. The results indicate that this kind of hydrophobic nano-CaCO₃ coating effectively protected the sandstone from the deleterious effects of acid rain.

Nowadays, the application of Fungi as a bio-mediated soil improvement technique is developing. The hydraulic properties of Rhizopus Fungi-Mycelium Treated Soil are unknown, and the treated sample tends to have low durability. This article presents experimental results on the hydraulic conductivity and shear strength of Fungi-mycelium-treated silica sand. The fungi used in the experiments are a combination of Rhizopus oligosporus and Rhizopus oryzae, which are popular for making Tempeh, a local soybean cuisine from Indonesia. The samples were prepared by mixing the sand with Tempeh inoculum at various treatments and Tempe inoculum and rice flour dosages for enhancing the durability of the treated soil. The results showed that the saturated permeability of the treated soil could be reduced by about 10 times compared to the untreated soil. In addition, the Soil-Water Characteristic Curve of the treated soil also developed. The effect of the fungi appears to fill the void of soil and hence increases the Air Entry Value and residual suction of soil. The curing method outside the mold (O-method) with 10% Tempeh inoculum, and 5% Tempeh inoculum with 5% rice flour is proven can extend the durability of the treated sample, the undrained compressive strength is about 40 kPa on day 14. Scanning electron microscope was performed on the samples, which lasted for 4 months. The mycelium and hyphae are still clearly seen covering all sand particles with different percentages of Tempeh inoculum and rice flour. When the mycelium covered all the sand particles and filled the pores, the water flow was partially blocked. It might be attributed to the strong hydrophobicity of the fungi, which could prevent water from penetrating the soil.