ABSTRACT Using cement with fibers is a cost-effective way to improve soft clays’ engineering properties. This study investigates the strength, stiffness, and durability of artificially cemented alluvial clay stabilized with glass fiber. Unconfined compressive strength and shear wave velocity tests were used, along with microstructural analysis via scanning electron microscopy and energy-dispersive spectroscopy. Durability and resistance to harsh weather were evaluated using wet-dry cycles. The combination of cement and glass fiber improved the mechanical response, with 0.4% glass fiber being the most effective. A blend of 0.4% glass fiber with 13% cement showed the highest strength and stiffness improvement and reduced mass loss. This mixture, supported by unique power functions forecasting its properties, is suitable for various civil engineering projects, such as unbounded sub-layers, highway barriers, stone columns, and ground improvement.

ABSTRACT Colloidal silica is a relatively new grouting low-carbon material used in soil improvement projects. A series of mechanical tests on a sand with different solid contents of the binder, i.e. 40, 30 and 20% solid content have been performed. Unconfined compressive strength at 7, 28 and 56 days, shear tests and permeability tests at 7 days were assessed. A statistical interpretation of these data has been performed and values were interpreted. A mathematical prediction model was suggested to estimate the mechanical strength of the grouted sand as the dilution grade varies. Furthermore, some considerations useful for geotechnical design on the evolution over time of the mechanical characteristics of the grouted sands have been carried out. Results show, from a statistical and mathematical view, that colloidal silica is a promising binder for ground improvement applications.

ABSTRACT When a material is subjected to cyclic loading, there are changes in the material’s geomechanical behaviour that need to be characterized for a safe design. For unbounded granular materials, the shakedown theory is used to explain the soil’s behaviour under cyclic loading. However, it is not clear yet if such theory is extendable to unreinforced and fibre-reinforced stabilized soils. To this end, a series of unconfined compression cycling loading tests were performed, to study the effect of the number of cycles and initial deviatoric stress level on the behaviour of an unreinforced and reinforced stabilized soil. The results were analysed in terms of shakedown theory, elastic and plastic deformation energy and damping ratio. It was observed that shakedown theory seems to represent the behaviour of the stabilized unreinforced and fibre-reinforced soils under cyclic loading, with threshold between the plastic shakedown and the plastic creep shakedown behaviour at around an absolute axial strain 1 × 10–3. The effect of increasing binder content (from 12 to 39%), comparable to reducing the initial deviatoric stress level (from 85 to 15%), promoted a reduction in plastic deformation (from 2.09 to 0.19% without fibres, and 2.21 to 0.24% with fibres) and damping ratio (from 25.17 to 10.01% without fibres, and 29.18 to 15.95% with fibres) due to the lower degradation of the solid matrix. It also promoted an increase in the difference between elastic and plastic energy (from − 1.04 to 13.92 kJ/m3 without fibres, and − 1.68 to 10.19 kJ/m3 for the first cycle).

ABSTRACT Piles are designed to support direct loads, however, floating piles in clay are often subjected to indirect loading (surcharge). In this case, the pile’s shaft will be subjected to negative skin friction on part or on its full length, depending on the value of the surcharge, soil condition and pile’s length. The total negative skin friction acting on the pile’s shaft is known as the drag-load, which will reduce the pile capacity and perhaps pull the pile out of its cap, leading to catastrophic failure of the structure. A numerical model was developed using the finite element technique to simulate the case of a single pile floating in clay subjected to surcharge. The model utilizes the concept of the Critical State Soil Mechanics (CSSM) and the constitutive law of the Modified Cam Clay (MCC). The MCC is capable of incorporating the effect of soil deformation and the stress history into the stresses acting on the pile’s shaft. It is widely used in modelling geomechanics problems. The objective of this study is to determine the location of the neutral plane on the pile’s shaft for a given surcharge, soil condition and pile’s length. Thus, the positive and negative skin frictions acting on the pile’s shaft can be determined and accordingly the pile capacity. After validating the numerical models with the data available in the literature, the model was used to generate a wide range of data, which commonly used in practice, to examine the effect of the parameters which govern the location of the neutral plane for these piles. Design charts and design example are presented.

ABSTRACT Expansive soils like Black Cotton Soil, exhibit numerous engineering hurdles due to their high swell-shrink behaviour, resulting in structural instability. Traditional stabilization techniques often prove inadequate and available nanomaterials are expensive, creating a demand for a cost-effective and eco-friendly stabilizer like nano rice husk ash (nRHA). This study tackles the challenge of stabilizing expansive soil using nRHA, synthesized via two distinct ball milling methods. Various concentrations of nRHA (0%, 0.2%, 0.4%, 0.6%, 0.8%, and 1.0%) were tested to assess their effectiveness in reducing the swell-shrink behaviour of Black Cotton Soil.r Result indicate that a 0.4% dosage of 2 + 5 hours nRHA (n 2,0.4) significantly decreases the soil’s swell-shrink potential. This treatment triggers the formation of Calcium Aluminium Oxide (CAO) and Calcium Aluminium Silicate Hydrate (CASH) gels, validated by X-ray diffraction (XRD) and Scanning electron microscope (SEM) analysis. This study advances nRHA treatments in enhancing the swell-shrink behaviour of expansive Soil.

ABSTRACT Sludge-cured lightweight soils have unique advantages in roadbed treatment due to their properties such as low density and high strength. Its long-term mechanical law based on the superposition of drying-wetting and freezing-thawing (D-W-F-T) is studied through creep experiment. The test results show that: with the increase of the number of D-W-F-T, the deformation of the soil gradually increases, and the deformation tends to be stable when it reaches a certain number of times; the stress-strain isochronous curves are obviously nonlinear in general; The long-term strength increases with the increase of density and confining pressure, and decreases with the increase of the number of D-W-F-T; by comparing the isochronous stress-strain curve cluster method and the steady state creep rate vs. The comparative analysis suggests that the steady state creep rate versus stress level curve method be used to determine the long term strength.

ABSTRACT Granular media, though discontinuous and heterogeneous, exhibit discrete behaviour at the grain scale and continuum behaviour at the macroscopic level. Understanding the correlation between micro-macro-mechanical parameters is crucial. The Discrete Element Method (DEM) effectively bridges this micro-macro-mechanical gap. This study simulates the Direct Shear Test (DST) using DEM software PFC2D on synthetic cemented granular media (CGM) under varying normal loads and strain rates. It examines micromechanical features and correlates them with macroscopic observations, focusing on confinement pressure and strain-rate dependency. Significant volumetric dilation is observed during shearing at low normal loads, which diminishes at higher normal loads. Particle-scale shear mobilization is explored through shear band formation in the sample. Grain-scale contact force distribution is highly heterogeneous throughout the sample. A probability distribution study is carried out to explore the bond breakage effect on the global response, which confirms the bond breakage to be a pressure and strain-dependent phenomenon.

ABSTRACT This study investigates the slope stability of Bingöl open-pit iron mine slopes using 3D limit equilibrium and finite element methods. The pit benches are 3 m wide and 6 m high, with an overall slope angle of 38°. The geological composition comprises slightly to moderately weathered and heavily jointed phyllite, micaschist, and gneiss. Shear strength parameters were determined through back analyses of already failed sections using the Hoek-Brown failure criterion and Geological Strength Index (GSI). Factor of safety values for static and dynamic conditions were calculated using 3D limit equilibrium and 2D finite element analyses. Results show good agreement between the two methods, with benches in the northern section exhibiting a significant decrease in safety factor under dynamic conditions, indicating near-limit equilibrium slopes.

ABSTRACT Understanding the load transfer and deformation mechanisms within geosynthetic-reinforced embankment overlying voids is fundamental for improving the current design methods. Based on geotechnical centrifuge tests, the numerical study highlights the cavity opening procedures within reinforced systems. Two procedures were studied: the increasing-diameter and gradual movement ones. For the gradual opening process, a cubic function is found to be well-suited, while a combination of cubic and quadratic functions is more appropriate for a progressive opening process. The study sheds light on the understanding of the load distribution over the cavity expansion. The soil arch formation occurs when the height reaches 2.5 times the sinkhole width. A triangular shape is found to be suitable for describing a progressive opening process, while an inverse triangular shape is more appropriate for a gradual opening process. Appropriate functions are utilized to fit the deformed geometry of the soil surface and of the deflected geosynthetics.