The use of nano-materials as a stabilizing agent in soils has a significant role, particularly in improving their mechanical properties. This study investigates the impact of stabilization using nano-materials, specifically nano-cement, on natural and contaminated clays. A series of laboratory tests, including Atterberg limits, compaction, unconfined compressive strength, permeability, and consolidation, are conducted to evaluate the soil properties. Various percentages of nano-cement (0 %, 0.5 %, 1 %, 1.5 %, and 2 %) are added to two sample groups; one prepared with water and the other with leachate. Based on the results of Atterberg limits tests, adding 2 % nano-cement to natural clay increases the liquid limit by 8.6 % and decreases the plasticity index by 16 %. These values diminish to 8.3 % and 13 % for contaminated clay. Furthermore, according to the compaction test results, increasing nano-cement content by up to 2 % leads to a reduction in maximum dry density by about 11.5 % and an increase in optimum moisture content by about 15.9 %. However, these values change to 5.77 % and 32.25 % for contaminated clay. The results indicate that increasing nano-cement content generally improves the strength and stiffness of the soil while reducing its permeability. On the other hand, contamination of the soil leads to a reduction in strength and stiffness, while permeability increases. Based on the Field Emission Scanning Electron Microscopy (FESEM) analysis, the incorporation of nano-cement improved the microstructure by decreasing pore spaces and enhancing bonding between particles. While chemical complexity of leachate negatively affects nano-cement dispersion, which leads to increased particle aggregation.

Granite residual soil exhibits a tendency to collapse and disintegrate upon exposure to water, displaying highly unstable mechanical properties. This makes it susceptible to landslides, mudslides, and other geological hazards. In this study, three common biopolymers, i.e., xanthan gum (XG), locust bean gum (LBG), and guar gum (GG), are employed to improve the strength and stability of granite residual soil. A series of experiments were conducted on biopolymer-modified granite residual soil, varying the types of biopolymers, their concentrations, and curing times, to examine their effects on the soil's strength properties and failure characteristics. The microscopic structure and interaction mechanisms between the soil and biopolymers were analyzed using scanning electron microscopy and X-ray diffraction. The results indicate that guar gum-treated granite residual soil exhibited the highest unconfined compressive strength and shear strength. After adding 2.0% guar gum, the unconfined compressive strength and shear strength of the modified soil are 1.6 times and 1.58 times that of the untreated granite residual soil, respectively. Optimal strength improvements were observed when the biopolymer concentration ranged from 1.5% to 2%, with a curing time of 14 days. After treatment with xanthan gum, locust bean gum, and guar gum, the cohesion of the soil is 1.36 times, 1.34 times, and 1.55 times that of the untreated soil, respectively. The biopolymers enhanced soil bonding through cross-linking, thereby improving the soil's mechanical properties. The gel-like substances formed by the reaction of biopolymers with water adhered to encapsulated soil particles, significantly altering the soil's deformation behavior, toughness, and failure modes. Furthermore, interactions between soil minerals and functional groups of the biopolymers contributed to further enhancement of the soil's mechanical properties. This study demonstrates the feasibility of using biopolymers to improve granite residual soil, offering theoretical insights into the underlying microscopic mechanisms that govern this improvement.

The sustained intensification of agricultural production to meet increasing food, feed and fibre demands has aggravated soil deformation, thereby accelerating soil degradation. The conversion of some of these degraded arable lands to permanent grassland has been recommended to recover the soil functions. However, there is still a considerable gap in understanding the timeline for the effective recovery of degraded land in terms of its stability (resistance and resilience to disturbance). Moreover, the dynamics of the recovery process in ameliorative grasslands are still not fully understood. In this study, the physical, hydraulic, and mechanical properties including the coefficient of compressibility (Cn) and precompression stress were investigated in degraded arable land at three different depths (0-5, 10-15 and 20-25 cm) after 1-, 2-, 8-, 13-, 19-, and 25-years ameliorative grassland conversion. To fully understand and finalise the dynamics of the recovery process as a function of time since the amelioratory conversion, we combined the analysed data from 2 different sets of measurements (loading conditions) on samples predrained to - 60 hPa matric potential. The loading conditions were (a). static confined compression with normal stresses applied for 4 h in steps of 1, 20, 50, 100, 200, and 400 kPa without stress relaxation on each sample, and (b). dynamic - cyclic loading at 50 kPa with 30 seconds of loading and unloading (relaxation). We included data concerning porewater pressure dynamics under the cyclic loading condition to document possible changes in elasticity. Our results showed that settlement during loading and the elastic rebound during unloading were related to the sward age and the sampled depth. Before the cyclic loading experiment, higher values of effective stress were recorded in the older swards, but the values changed after loading in response to the change in the porewater pressure. The effective stress values were less negative during loading than when unloading. At soil depth of 0-5 cm in the 25 years old sward, the rebound rate (values) and the coefficient of compressibility were higher due to changes in soil properties, particularly the soil bulk density, while at the 10-15 and 20-25 cm depths, the mean values were much closer. When the rebound rate was considered, the highest mean value occurred at 13 years after conversion. In addition, significantly higher values of pre-compression stress were observed in the 8-year-old sward under static loading, which decreased by 19 years. Higher values of pre-compression stress were mostly recorded at the lower depths under static loading. Finally, the results showed that a period between 8 and 13 years is needed to document the starting of strength regain and the recovery of the physical properties and functions, after conversion to grassland. This recovery was observed even up to deeper depths of 20-25 cm for precompression stress and for the soil compressibility/ rebound in the top 5 cm

In this study, the fatigue damage to a power takeoff (PTO) shaft was evaluated under various operating conditions in rotary-tillage operations, considering soil strength and texture. Pearson correlation analysis was conducted to identify the significant variables influencing PTO shaft fatigue damage, and a prediction formula was derived through regression analysis using these variables. The PTO shaft exhibited increased shear stress with higher transmission gear stages, PTO gear stages, or soil properties, including strength and texture. The fatigue damage increased with higher transmission gear stages and soil strength while decreasing with higher PTO gear stages. Notably, as the PTO gear stage increased, the mean stress increased; however, the stress amplitude and equivalent completely reversed stress significantly reduced fatigue damage. Statistical analyses revealed a strong correlation between PTO shaft fatigue damage and factors such as tractor travel speed, PTO shaft power consumption, PTO shaft rotational speed properties, including strength and texture. The developed prediction equation, incorporating all significant variables, demonstrated, with a coefficient of determination (R2) of 0.93 and a root mean square error (RMSE) of 2.94x10-9. This equation effectively identifies trends in PTO shaft fatigue damage based on key operational variables. Furthermore, the findings emphasize the critical role of soil texture in assessing PTO shaft fatigue damage.

Microbially induced carbonate precipitation (MICP) represents a technique for biocementation, altering the hydraulic and mechanical properties of porous materials using bacterial and cementation solutions. The efficacy of MICP depends on various biochemical and environmental elements, requiring careful consideration to achieve optimal designs for specific purposes. This study evaluates the efficiency of different MICP protocols under varying environmental conditions, employing two bacterial strains: S. pasteurii and S. aquimarina, to optimize soil strength enhancement. In addition, microscale properties of carbonate crystals were investigated and their effects on soil strength enhancement were analyzed. Results demonstrate that among the factors investigated, bacterial strain and concentration of cementation solution significantly influence the biochemical aspect, while temperature predominantly affects the environmental aspect. During the MICP treatment process, the efficiency of chemical conversion through S. pasteurii varied between approximately 80% and 40%, while for S. aquimarina, it was only around 20%. Consequently, the CaCO3 content resulting from MICP treatment using S. pasteurii was significantly higher, ranging between 5% and 7%, compared to that achieved with S. aquimarina, which was about 0.5% to 1.5%. The concentration of the cementation solution also plays a pivotal role, with an optimized value of 0.5 M being critical for achieving maximum efficiency and CaCO3 content. The ideal temperature span for MICP operation falls between 20 degrees C and 35 degrees C, with salinity and oxygen levels exerting minor impact. Furthermore, although salinity influences the characteristics of formed carbonate crystals, its effect on unconfined compressive strength (UCS) values of MICP-treated soil remains marginal. Samples subjected to a one-phase treatment, adjusted to pH values between 6.0 and 7.5, exhibit roughly half the UCS strength compared to the two-phase treatment. These findings hold promising potential for MICP applications in both terrestrial and marine environments for strength enhancement.

The accurate quantification of the temporal changes in seabed strength allows for more reliable and less conservative geotechnical design. A recently developed effective stress framework, established within a one-dimensional computational domain to quantify changes in soil strength due to pore pressure generation and dissipation, has been extended to a twodimensional (2D) computational domain to allow for consideration of boundary value problems that are too complex to be simplified to one-dimensional conditions. The work to implement the 2D framework is reported across two companion papers. The first of the two papers utilises large deformation finite element analyses to quantify the spatial distribution of accumulated plastic shear strain. These distributions are encapsulated within a strain influence function that is used within the new 2D framework in this paper to calculate the extent and magnitude of excess pore pressure, and in turn the mobilised soil strength for a number of boundary value problems that represent typical offshore geotechnical processes. The merit of the new 2D framework is explored via retrospective simulations of existing experimental and numerical data. The resulting comparisons demonstrate the potential of the new framework, which is in quantifying the reliability of a range of geotechnical structures under complex loading conditions.

The undrained shear strength of contractive fine-grained soils changes with time, reducing due to pore pressure generation and increasing during consolidation. There is an increasing appetite to recognise these temporal soil strength changes in offshore geotechnical design, as it provides a basis for potentially less conservative designs. Contributions to this endeavour are reported across two companion papers. This first paper extends an existing effective stress framework that relates the generation of pore pressure to accumulated plastic shear strain, allowing undrained shear strength to be calculated within the context of critical-state soil mechanics. The main development is the extension of the computational domain to two dimensions, allowing calculations to be made for boundary value problems that cannot be satisfactorily simplified to onedimensional conditions. The magnitude and distribution of accumulated shear strain surrounding objects buried in soil are quantified through a series of large deformation finite element analyses. These spatial distributions are described using a strain influence function in the new 2D framework to calculate the extent and magnitude of excess pore pressure, and in turn the mobilised soil strength around the buried object. The performance of the 2D framework is examined in the companion paper through retrospective simulations of experimental and numerical data.

Landslide mitigation is one of the major challenges occurring in hilly and mountainous regions worldwide. Various civil construction-based options, such as constructing walls and making fences using wires and metallic mesh, are regularly employed in attempts to reduce the hazard, but these measures are temporary solutions to stop the movement of unstable soil. The problem of unstable soils could be solved by increasing the vegetation on the hilltops and mountains where soil erosion and mass movements are predominant. A bioengineering approach could resolve this problem in a sustainable way and without damaging the environment. Various methods and approaches have been adopted worldwide for landslide mitigation and are discussed and critically analyzed in this article. The effectiveness of bamboo plantations on the hilltops and the use of specific species as determined by the soil characteristics are discussed and elaborated. Some research gaps in the existing bioengineering aspects and scope of research are highlighted for further improvement and refinement.

The study investigates the use of spent coffee (SC), a post-consumer coffee waste, as a stabilizing material in combination with cement (C) for soil improvement. The study explores the influence of different maximum particle sizes of silty sand soil on the resistance behavior when stabilized with cement and various proportions of spent coffee. The substitution ratios used were 0%, 3%, 6%, 9%, and 12% of spent coffee in place of cement. Each replacement ratio was mixed with soils and cement at three different maximum soil sizes (0.6 mm, 2 mm, and 4.25 mm), with an optimum water content and a binder (SC+C) to soil ratio of 0.2. After curing for 14 and 28 days, the unconfined compressive strength (UCS) of the treated soil was tested. The results indicated that samples with up to 6% SC replacement maintained their strength or exhibited slight decreases throughout the curing period. However, at higher replacement ratio, the strength decreased. Additionally, increasing the maximum size of soil particles led to improved strength properties.

In recent years, there has been an increasing interest in investigating the use of non-traditional additives for stabilizing problematic soils. As the demand for eco-friendly alternatives to cement rises, magnesium chloride, a widely used deicer and dust suppressor, has emerged as a potential choice. This study aims to provide a comprehensive understanding of the microstructural changes that occur and affect the macro behavior of treated bentonite (B) and yellow marl (YM). To achieve this, MgCl2 solution was added to the soils at 3, 6, 9, and 12 percent by dry weight of the soil, and samples were cured for 7, 14, and 28 days at 5 degrees C, 25 degrees C, and 35 degrees C. The mechanical properties of the treated soils were then evaluated using the unconfined compression test, direct shear test, and pressure chamber test (SWCC), while microstructural analysis techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDAX), and Fourier transform infrared spectroscopy (FTIR) were employed to examine the mechanism of MgCl2 stabilization. The results indicate that adding MgCl2 and extending the curing period significantly increased both soils' unconfined compressive strength (UCS). However, the UCS value decreased for treated samples cured at temperatures higher than 25 degrees C due to an incomplete cation exchange process and the reduction of apparent cohesion. A part of the gained strength from apparent cohesion and matric suction in the unsaturated samples was lost when the samples reached full saturation during the direct shear test. Changes in the particle size, pore size, and pore void distribution due to the MgCl2 stabilization affected the SWCCs of the treated soils. Microstructural analyses revealed the formation of magnesium hydration products, such as magnesium silicate hydrate (M-S-H) and magnesium aluminate hydrate (M-A-H), which contributed to the strength increase by increasing grain size, filling the pores, binding fine particles within coarse grains, and forming a flocculated structure through recrystallization of MgCl2 and the formation of cementitious gel. Additionally, for B, adding MgCl2 led to soil flocculation through ion exchange, while for YM, the same process occurred due to the greater surface tension of the saline solution encircling the particles.