Climate change increases the frequency of extreme weather events, intensifying shallow flow-type landslides, soil erosion in mountainous regions, and slope failures in coastal areas. Vegetation and biopolymers are explored for ecological slope protection; however, these approaches often face limitations such as extended growth cycles and inconsistent reinforcement. This study investigates the potential of filamentous fungi and wheat bran for stabilizing loose sand. Triaxial shear tests, disintegration tests, and leachate analyses are conducted to evaluate the mechanical performance, durability, and environmental safety of fungus-treated sand. Results show that the mycelium enhances soil strength, reduces deformation, and lowers excess pore water pressure, with a more pronounced effect under undrained than drained conditions. Mycelium adheres to particle surfaces, forming a durable bond that increases cohesion and shifts the slope of the critical state line, significantly enhancing the mechanical stability of fungus-treated sand. The resulting strength parameters are comparable to those of soils reinforced with plant roots. Fungus-treated sand remains stable after 14 days of water immersion following triaxial shear tests, with no environmental risk from leachate. These findings demonstrated that fungal mycelium provides an effective and eco-friendly solution for stabilizing loose sand, mitigating shallow landslides, and reinforcing coastlines.

As the main by-product of wheat, wheat bran is mostly used as animal feed or incinerated, which adversely affects the environment. Mycelium-based biocomposites, which are mixtures of agricultural by-products (e.g., wheat bran) and fungi, minimize wheat bran wastage and have attracted attention as building materials owing to their high strength, low density, and environmental friendliness. Nonetheless, the practical application of mycelium-based materials in geotechnical engineering remains rudimentary. Building on mycelium-based biocomposites, this study develops lightweight sand-mycelium soil (LSMS), consisting of soil, substrate materials (wheat bran), and hyphae (P. ostreatus), as an eco-friendly lightweight backfill material in geotechnical engineering. The impact of substrate material content, effective confining pressures, and hyphae on the mechanical properties of P. ostreatus-based LSMS was studied. In addition, a detailed investigation of the formation mechanisms of P. ostreatus-based LSMS was conducted. The results indicated that increased substrate material content reduces the strength but increases the ductility of P. ostreatus-based LSMS. The presence of hyphae alters the structure of P. ostreatus-based LSMS, reducing volumetric contraction and improving strength, although this depends on confining pressure. The formation of P. ostreatus-based LSMS involves biophysical mechanisms (hyphal network bundling and filling of void spaces) and biochemical mechanisms (self-bonding, secretion bonding, and aragonite deposition). Biochemical mechanisms may provide a more prolonged effect on the stability of P. ostreatus-based LSMS compared to biophysical mechanisms. P. ostreatus LSMS shows great potential as an eco-friendly alternative to conventional lightweight backfill materials in geotechnical engineering.

The disposal of tailings in a safe and environmentally friendly manner has always been a challenging issue. The microbially induced carbonate precipitation (MICP) technique is used to stabilise tailings sands. MICP is an innovative soil stabilisation technology. However, its field application in tailings sands is limited due to the poor adaptability of non-native urease-producing bacteria (UPB) in different natural environments. In this study, the ultraviolet (UV) mutagenesis technology was used to improve the performance of indigenous UPB, sourced from a hot and humid area of China. Mechanical property tests and microscopic inspections were conducted to assess the feasibility and the effectiveness of the technology. The roles played by the UV-induced UPB in the processes of nucleation and crystal growth were revealed by scanning electron microscopy imaging. The impacts of elements contained in the tailings sands on the morphology of calcium carbonate crystals were studied with Raman spectroscopy and energy-dispersive X-ray spectroscopy. The precipitation pattern of calcium carbonate and the strength enhancement mechanism of bio-cemented tailings were analysed in detail. The stabilisation method of tailings sands described in this paper provides a new cost-effective approach to mitigating the environmental issues and safety risks associated with the storage of tailings.

Soil stabilization is a method of improving weak soils by adding different additives. Nano additives and materials represent a new technology and a revolution in soil mechanics and geotechnical engineering, used for soil stabilization, a branch of soil improvement. This research evaluates the particles of Nano- and Pico-Typha solution as a new biomaterial for soil improvement using nano and pico scales, bio, and soil mechanics tests. The research investigates the changes in soil mechanical properties after the addition of Nano and Pico Typha solution as a Nano-Bio Geotechnics (NBG) technique, comparing the properties of the soil before and after stabilization. To control and characterize the size and nature of the particles studied in this research, SEM tests were performed after the nano production process. To check the particle dimensions and structure before and after the nano production process, XRF and XRD tests were performed. After converting particles from micro to nano scale, there are also smaller pico particles. The research studied the properties of Khavaran clay soil by adding Typha and Nano Typha as a Nano-Bio additive in different percentages of 3%, 5%, and 7%, and in curing times of 1, 7, and 28 days. The results showed that the uniaxial resistance of clay increased from 50 kPa to 12 times its initial value by adding 7% Nano-Typha after 28 days of curing. The maximum deviator stress of the soil increased by 10.1, 14.07, and 15.9 times its initial value in confining stresses of 100, 200, and 300 kPa, respectively, by adding 7% Nano-Typha after 1 day of curing. The cohesion and friction angle of the soil stabilized with 7% Nano-Typha solution increased by 2.22 and 6.3 times, respectively, compared to clay soil after 1 day of curing.