The presence of expansive soils on construction sites is problematic in geotechnical engineering. The swell-shrink behaviour makes these soils not suitable to be used in their natural state. The expansive soil damages cause financial loss yearly more than floods, hurricanes, tornadoes, and earthquakes combined. Moreover, the cost of cut to spoil of expansive soils during construction projects has continued to rise because of the high cost of earthworks, haulage, and the increasing scarcity of spoil areas because of the built environment. Nonetheless, a proper stabilization technique can significantly enhance the expansive soil's properties. The research project attempts to review, report the limits and merits of mechanical and chemical methods utilized to stabilize expansive soils in line with their efficiency, environmental concerns, and cost-effectiveness. A review of mechanical and chemical treatment techniques is conducted in this regard. Ultimately, each stabilization method exhibits its merits and limitations. The lack of standards for the treatment of swelling soils is a significant problem in engineering practice. Specialists in the domain of soil treatment must work together to obtain an optimized stabilization approach and protocol. Moreover, engineers should perform a geoenvironmental assessment appropriate for chemical stabilization methods and additives utilized. This research work contributes as a guideline in the selection and application of chemical and mechanical stabilization methods.

The behaviour of unsaturated soils is mainly influenced by suction. When unsaturated soils display swelling properties, it becomes fundamental to investigate the impact of soil suction on the swelling stress. A survey was done across Free State province in South Africa and samples were obtained from Bloemfontein, Winburg, and Welkom. Geotechnical studies were performed on particle size definition, free swell ratio, free swell index, Atterberg limits, X-ray diffraction, proctor compaction test, soil suction measurement, and constant volume swelling tests to determine the physical and hydro-mechanical properties of the soil samples. According to the findings, at the optimum water content, the swelling stress values are in the range of 177 kPa to 326 kPa which is more than the bearing limit (~ 40 kPa) applied for most lightweight footing. Smectite is identified as the predominant clay mineral in the study areas and has a key influence on the swelling properties. A solid relation is observed between the swelling stress and the soil suctions, with a correlation coefficient value greater than 80 %.

The study aims to propose a mathematical approach to determine the optimum moisture content (W OP ) and the corresponding maximum dry unit weight (γ dmax ) of unsaturated fine-grained clay soils with accuracy. Laboratory tests such as grain size distribution, Atterberg limits, specific gravity, Proctor compaction test, and soil suction measurement are conducted to assess soil properties. The W OP and γ dmax are determined using the mathematical approach based on differential function (∂) and the graphical method. The differences in optimum moisture content values between the mathematical approach and the graphical method (∆W OP ) values are 0.43 %, 0.36 %, 0.42 %, 0.24 %, respectively for soils PES, BFS, WIS, BES, and induced differences in total suction of 179.17 kPa, 144.00 kPa, 175.00 kPa, 96.00 kPa, respectively for soils PES, BFS, WIS, BES. Moreover, the differences in matric suction are 148.27 kPa, 116.13 kPa, 144.83 kPa, 80.00 kPa, respectively for soils PES, BFS, WIS, BES. ∆W OP and ∆ γdmax values are smaller than 0.5 % and marginal in the context of saturated soil mechanics. However, the total suction and matric suction values induced by ∆W OP values are significant for unsaturated soils. An accurate estimation of γ dmax and W OP can be performed on unsaturated compacted soils using the mathematical approach.

The stress raisers factor around circular holes in a plate exposed to uniform tensile load at the edges has been studied using Finite Element Analysis solvers. The effect of mesh quality on stress raisers factor, the maximum Von Mises stresses, the computing time, and the percentage error has been examined. 4 Node Quadrilateral Element and 8 Node Quadrilateral Element were utilized respectively as first-order component (4NQE) and higher-order component (8NQE) to assess the maximum Von Mises stress and the numerical stress raiser factor (Kn) at various mesh sizes. The maximum Von Mises stress and the stress raiser factor were determined using the following finite element solvers: ABAQUS, ANSYS, CATIA, STRAND 7, ALGOR, COSMOS/M, and FEMAP. The estimations of the numerical stress raiser factor (Kn) were compared with the theoretical stress raiser factor (Kt). There were discrepancies observed between the maximum Von Mises stresses of the FEA solvers.

The behaviour of heaving soils is generally governed by the matric suction. Nonetheless, the mineralogical characteristics influence the geotechnical behaviour. X-ray diffraction is a common technique used to determine the mineral composition. This equipment is costly and the process time-consuming. The objective of this research is to develop predictive mathematical models to determine the predominant minerals in heaving soils. Soil samples are collected from identified areas across Free State province by digging at 50 cm depth from the ground surface. Geotechnical lab studies such as particle size distribution, Atterberg limits, specific gravity, free swell ratio, free swell index, linear shrinkage, and X-ray diffraction are performed to evaluate soil properties. A stepwise analysis is conducted to determine the response of each type of mineral to soil properties, and select the best subsets. Moreover, the influence of soil minerals on soil properties is achieved by investigating the correlation between the relevant soil properties and each mineral. Multivariate regression is performed utilizing MINITAB 18 program to develop mathematical predictive models. These equations are assessed base on correlation coefficient, probability value (P-value), and standard residual pattern analysis. The predominant minerals can be assessed with acceptable accuracy utilizing the proposed semi-empirical models.