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Skirted footings are used to increase the final carrying capacity of shallow foundations resting on unstable soil and to decrease settling by limiting the soil beneath them. Skirted footings are utilized as an alternative to pile driving in poor strength soils at the top layer, such as gypseous soil, to save project costs and time spent installing piles while maintaining excellent performance. The settling of circular skirted footings resting on gypseous soil subjected to loading, infiltration, and collapsing stages was investigated using numerical calculations in this research study to determine their stability under environmental loadings. Finite element analyses were carried out using the commercially available software GEO-STUDIO. The stage of gypseous soil and variable skirt depth to footing diameter ratios (d/D) were taken into consideration. The findings reveal that both the soil stage and the skirt embedment ratio have a substantial impact on the ultimate bearing capacity and the settlement of weak soil, with the skirt embedment ratio increasing resulting in superior skirted footing performance. Furthermore, the improvement in settlement for the loading stage is the smallest, whereas the value for the collapsing soil stage is the largest.

Searching for the best soil stabilizer to overcome problems occur by the soft soils are still being the main concern, not only to achieve the required soil engineering properties but also by considering the cost and the effect to the environment. This review paper presents the results of experimental researches on soil stabilization by using the most chemical admixtures, which involved cement, lime and fly ash, and their effectiveness in the engineering properties of soil. Based on the literature review, the results show that addition of these chemical additives lead to significant improvement in workability, strength, durability and mechanical behaviour. On the other hand, it lead to a reduction in shrinkage, plasticity, compressibility and swell characteristics of soil. Also, the curing duration had significantly improved the strength properties of the stabilized soil with chemical additives. Using of each chemical additive and its suitability for a specific soil is highlighted in the research.

Many of gypsum soils have existed in arid and semi-arid lands. It is considered one of the most problematic soils because of its complicated and unpredicted behavior when exposure to moisture. Extensive researches have been conducted in Iraq to observe the behavior of such soil and to suggest safety restrictions for the collapse and set practical precautions for the structures. This study investigated the effect of gypsum content on some unsaturated engineering properties of a clayey soil. Three different proportions of gypsum (0%, 5% and 20% by weight of the parent soil) were added and tested. The samples have been subjected to swelling potential test, soil water retention curve (SWRC), vapour diffusion and shear strength parameters. It is observed that gypsum content has a significant influence on SWRC, whereas, soil that has high gypsum content made SWRC with higher variables represented by air entry values and residual state. On the other hand, an increase in gypsum content led to a reduction of swelling potential and shear strength parameters. The results of vapour diffusion indicate that gypsum content could modify the microstructure in an unsaturated state and reduce the vapour diffusion through the soil.

Soil–water characteristic curves (SWCC) can be defined as the relationship between the water content and suction of an unsaturated soil. It considered a basic relation to explanation of the engineering behaviour of unsaturated soil such as hydraulic conductivity and shear strength, So the study of SWCC is useful to reduce the time and cost of unsaturated soil testing for different engineering purposes. An approach model has been used to predict the SWCC for different soils. The influence of the soils on SWCC shape, the unsaturated hydraulic conductivity and shear strength parameters have been studied in this paper using mathematical models. The results of SWCC show that suction of clay soil is bigger than sandy soil, while the clayey silt soils exhibit an intermediate behaviour at same water content. The values of unsaturated shear strength are increasing while the unsaturated hydraulic conductivity is decreasing with increasing soil suction. This behaviour of the last two parameters with soil suction should be taken in consideration for engineering purposes.