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.

While many employ a hyperbolic stress-strain relationship for soils, it is known that such a relationship is accurate over either the small strain range as encountered in earthquake and soil dynamics problems or a relationship with different input parameters that are needed over large strains as is required for finite element analyses of large deformation behavior. The two characterizations do not become one. A proposed power relationship is presented that was developed to characterize the triaxial test stress-strain behavior of cohesionless material from lubricated or frictionless cap and base tests (some 144 tests) covering a range in the natural variation in particle size, particle shape and surface roughness, over low to high confining pressure. This relationship covers the range in strain from 10(-6) to soil failure. It has been used successfully to date in laterally loaded pile response characterization (the Strain Wedge Model) and shallow foundation load-settlement-bearing capacity response. Most recently, it has been extended to assess the behavior of rock-like material (caliche). The relationship and its comparison with the hyperbolic relationship for large strain and the shear modulus reduction curve for seismic behavior are presented here.

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.

Enzyme-induced carbonate precipitation (EICP) has emerged as an environment-friendly solution for soil improvement. As a composite material, it is challenging to determine the micromechanical properties of EICP-reinforced sand using common macromechanical tests. In this work, a systematic study was conducted to determine the micromechanical properties of EICP-reinforced sand. The development of the micromechanical properties obtained from indentations along the route of sand particle-CaCO3-sand particle was examined. The width of the interfacial transition zone (ITZ) in EICP-reinforced sand was investigated. The effect of the reaction environment on ductility (i.e., the ratio of elastic modulus over hardness) of CaCO3 was investigated. The experimental results have identified that the width of ITZ in EICP-reinforced sand ranges from 0 to 180 mu m, which is significantly influenced by the crystal crystallinity or crystal morphology of CaCO3. The presence of porous media (i.e., sand particles) leads to the decrease in impurity content in the crystal formation environment, resulting in the lower ductility of CaCO3 accordingly. The mean value of fracture toughness of CaCO3 precipitation was identified to be the lowest one among sand particles, CaCO3 precipitation, and sand particles-CaCO3 interface. The lowest fracture toughness of CaCO3 indicating the failure of biocementation is derived from the CaCO3-CaCO3 breakage.

Whole-life geotechnical design accounts for the evolution of geotechnical properties due to the actions imparted on the infrastructure during the design life to improve design outcomes. In fine-grained soils, geotechnical properties evolve as a result of cyclic softening from excess pore pressure generation under undrained cyclic loading, and hardening during subsequent dissipation. Traditionally geotechnical design has focused on reduced strength and stiffness from softening, overlooking beneficial effects of hardening leading to increases in strength and stiffness. This paper presents a surrogate model that can capture the evolution of geotechnical properties of normally and lightly over consolidated clays through episodes of undrained pre-failure cyclic loading with intervening consolidation, validated against laboratory element test results. The surrogate model is shown to capture the essential elements of the whole-life soil-structure interaction, which include: (i) the excess pore pressure generated during undrained cyclic loading and the associated soil softening; (ii) the reduction in void ratio caused by the dissipation of excess pore pressured during the consolidation process; and (iii) the evolution of undrained shear strength and stiffness through these processes. The surrogate model allows rapid estimation of evolving soil properties in design, enabling automated optimization of geotechnical design calculations (such as required size of foundations or anchors), and use in probabilistic analyses such as Monte Carlo approaches, to quantify the influence of uncertainty in loading history and geotechnical parameters on system reliability.

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 preand 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.

Biochar (BC) is an eco-friendly material produced through coal pyrolysis and can improve the mechanical properties of cement-based construction and building materials. This research study explored the effects of BC and natural sand (Sand) replacement on the improved static and cyclic response of blended hydraulic cement (BHC) stabilized soft clay (SC) as a greener subgrade material. Unconfined compressive strength (UCS), indirect tensile stress (ITS), and indirect tensile fatigue life (ITFL) of the BHC-stabilized SC-BC-Sand samples were examined. Adding 10% BC to the BHC-stabilized samples was found to enhance cementitious products due to its porous structure and high water absorbability. The UCS, ITS and ITFL at this optimum ingredient were improved up to 315%, 347% and 862%, respectively, compared to the BHC-stabilized SC. Fourier transform infrared spectrometer, thermogravimetry differential thermal analysis and a scanning electron microscope with energy- dispersive-ray spectroscopy analyses the BHC-stabilized sample at the optimum ingredient showed the highest C-S-H and Ca(OH)2 2 in the pores. This investigation will encourage the utilization of BC to create both environmentally friendly and durable stabilized subgrade material.

Road infrastructure plays an important role in strengthening transportation and driving the economic advancement of countries. However, the increasing traffic volume has accelerated road deterioration, particularly at critical points like bridge-road junctions. Traditional repair methods involving demolition and reconstruction lead to extended closures and high costs. This study explores the polyurethane (PU) foam injection technique as an alternative solution, which can reduce both repair time and costs. The research evaluates the application of PU foam in various road projects across Thailand, highlighting its ability to repair pavement surfaces and structures, even in severely damaged areas. Despite its advantages, the use of PU foam faces challenges due to a lack of standardized quality control. This paper proposes a set of working guidelines for PU foam injection, aimed at key stakeholders such as the Department of Highways, the Department of Rural Roads, and the Department of Local Administration. The findings underline the importance of establishing standardized methods to ensure the long-term effectiveness of PU foam in road maintenance. Future research should focus on refining these guidelines for diverse road conditions to support the sustainable development of national transportation infrastructure.