Swelling soils are increasingly recognized as a critical issue in geotechnical engineering, as their presence can lead to substantial damage to built structures. When structures are built on such soils and free swelling is prevented, stresses can develop that may lead to significant damage to the structure. Soil stabilization through the use of additive materials has garnered considerable attention as an effective method for mitigating this problem. The objective of this study was to stabilize the clay soil (CH) with high swelling potential by using sea shell, lime and zeolite additives in two stages. In the initial phase, consistency limits were tested by mixing high plasticity clay soil mixed with 8-10-12-14-16% sea shell 0-3-5-6-8% lime (one of the most used soil stabilizer) and 0-5-10-15-20% zeolite by weight. The three mixtures and the two best percentages determined for each mixture were then combined. Upon completing these steps, five experimental sets were prepared by combining the percentages that yielded the best results. Compaction test, percent swelling test and swelling pressure tests were performed with these datas. According to the test results, adding 14% sea shell, 6% lime and 5% zeolite by weight (SS14L6Z5) gave the smallest swelling value as 1,07% and highes swelling pressure as 23 kPa. This study concludes that the combined use of these additives led to a substantial 96% increase in swelling pressure, along with a marked reduction in swelling potential.

This research presents an in-depth analysis of the volumetric and mechanical behavior of expansive soils surrounding the Khangiran gas well in Sarakhs, emphasizing the effects of matric suction and confining pressures on soil mechanical properties. The study employs both laboratory and numerical approaches, utilizing an unsaturated triaxial apparatus and GeoStudio software, to assess (1) the influence of matric suction and confining pressure on volumetric deformation and shear strength, (2) the impact of annual precipitation on soil swelling, and (3) the tensile stresses exerted on the well casing due to soil expansion. Laboratory results reveal that shear strength increases from 195 kPa to 235 kPa as confining stress rises from 100 to 200 kPa, while cohesion climbs from 68 kPa in saturation to 95 kPa under 100 kPa of matric suction, signifying enhanced resistance in drier soil conditions. Numerical modeling indicates that annual precipitation induces a maximum tensile force of 163 kN at a depth of 13 m, with the expansive zone extending approximately 15 m from the well. The thickness of the steel used for tensile strength resistance against soil swelling is sufficient, and if extensive corrosion of the steel casing is not a concern, tensile strength failure will not occur. These findings offer critical insights into soil-structure interaction in expansive soils and provide practical guidance for the design of resilient gas well casings in similar geotechnical settings.

Internal erosion is one of the most important factors that cause earth structures that retain water, such as embankment dams, to collapse. Concentrated leak erosion, one of the forms of internal erosion, occurs in cracked fine-grained soils and pressurized flow conditions. To evaluate the concentrated leak erosion risk of cracks/voids, it is necessary to ascertain the erosion resistance of these materials. The erosion rate and critical shear stresses determine internal erosion resistance in concentrated leak erosion. This study determined soil's concentrated leak erosion resistance using test equipment that allowed the flow to pass through a hole with stress-free (no loading), anisotropic-compression stress, anisotropic-expansion stress, and isotropic stress conditions. The stresses that developed in the samples' hole wall where erosion occurred were determined with numerical modeling as pre-experimental stress conditions. The experiments were performed under a single hydraulic head on four selected cohesive soils with different erosion sensitivity. Time-dependent flow rates obtained from the test system can be used to determine hydraulic parameters, such as energy grade lines, with the help of basic theorems of pipe hydraulics in theoretical hydraulic models. Moreover, the erosion rates were quantitatively determined using the continuity equation, while critical shear stresses were qualitatively compared for concentrated leak erosion developed by the dispersion mechanism. As a result of the experiments, stress conditions influence the concentrated leak erosion resistance in the soil samples with dispersive erosion. Moreover, the shear strength in the Mohr-Coulomb hypothesis can explain the erosion resistance in these soils under stress conditions depending on the sand/clay ratio.

The risk of geohazards associated with frozen subgrades is well recognized, but a comprehensive framework to evaluate frost susceptibility from microstructural characteristics to macroscopic thermo-hydro-mechanical (THM) behaviors has not been established. This study aims to propose a simple framework for quantitatively assessing frost susceptibility and compressibility in frozen soils. A systematic THM model was devised to predict heat transfer, soil freezing characteristics, and stress states in frozen soils. Constant freezing experiments and oedometer compression tests were performed on bentonite clays under varying temperatures (-5 degrees C, -10 degrees C, and -20 degrees C) and stress levels to validate the proposed model. Additionally, soil electrical conductivity measurements were employed to assess the temperature- and stress-dependent volumetric and mechanical properties of frozen soils. The model used Fourier's law to compute the transient soil temperature profile and estimated the volume change and stress states based on the soil freezing characteristic curve. Experimental results showed that frost heave of bentonite reached between 9.0% and 26.6% of axial strain, which was largely predicted by the proposed model. It also demonstrated that the frost heave was mainly attributed to the fusion of the porewater. Additionally, the preconsolidation pressure of frozen soils exhibited a rapid increasing trend with decreasing temperature, which was explained by the temperature-dependent ice morphology in the soil interpore. Furthermore, the findings also demonstrated a remarkable sensitivity in the electrical conductivity in response to the soil temperature during the frost heave process and the stress state under the loading or unloading path.