**5. Conclusions**

**4. Previous related studies**

96 Current Topics in the Utilization of Clay in Industrial and Medical Applications

Clay soils are important in the construction of buildings, dams, roads, airports, pavements and highways [25–34]. Soil problems encountered in geotechnical engineering need to be solved. Because of its double layer, clay can absorb water 10–500 times its own weight. In addition, it is considered to be a problematic soil that can show settlement under loading, with swelling or compression when it receives water. Karmi et al. [26] investigated two case studies of embankment dams in Iran. Researchers indicated that for large dams, the internal friction angle plays a more critical role in stability analyses than the cohesion parameter. Çabalar [28] investigated various fine contents and their effects on the triaxial behavior of coarse sand. Consequently, the high compressibility and other clay-like behaviors of mixtures were attributed to the particle characteristics (size and shape). Shanyoug et al. [31] investigated the effects of fine contents on the mechanical behavior of completely decomposed granite during dynamic compaction grouting. Consequently, researchers indicated that the

Naik et al. [32] investigated the settlement of an institutional building located in South Goa, India. This building developed cracks when the construction reached the beam level. Some foundations were located in unconsolidated filled ground, according the standard penetration test, and thus, differential settlement was observed in the foundations. Dafalla [34] investigated the cohesion and angle of internal friction for granular soils using the direct shear test for different clay contents and different moisture contents. Consequently, researchers observed a steep drop in both cohesion and angle of internal friction in a moist, clay-sand mixture when the clay content was high. In addition, many researchers have studied the geotechnical engineering behavior of clays and their microstructure [35–39]. Rajasekaran et al. [35] investigated the influence of lime and sodium hydroxide on the microchanges in two marine clays using scanning electron microscopy (SEM). These researchers suggested that the

Horpibulsuk et al. [36] investigated the strength development and microstructural changes of stabilized, silty clay. SEM, mercury intrusion and thermal gravity analyses for qualitative and quantitative analyses of the sample microstructures were conducted in this research. Researchers suggested that the volume of large pores increased due to the presence of coarser particles in a short period, whereas the volume of small pores decreased due to the solidification of the hydrated cement. Some studies indicated that Atterberg's limits and grain-size distribution are indicators of the soil mineralogy and for the determination of many fine-grained soil properties [37–38]. Simultaneously, Atterberg's limits affect grain-size distribution and mineral composition. For example, an increase in the surface area is observed with increased liquid limits [37, 40–43]. Grabowska-Olszewska [44] investigated the relationship between the colloidal activity and the specific surface area of model soils of kaolinite and bentonite mixtures. Researchers observed that when the clay fraction increases, the total surface area also increases. Rahardjo et al. [45] investigated the index property and engineering property tests on residual soils from two major geological formations in Singapore. These researchers suggested that that the variations in the index and engineering properties of the residual soils

addition of lime and sodium hydroxide created an optimal pozzolanic reaction.

compaction efficiency increases with the increasing fine content.

Geotechnical engineering is one of the most important parts of any kind of construction. No matter how well the superstructure is projected, there is no sense in beginning construction if the ground materials are not considered. As Karl Terzaghi said in 1939, *"…In engineering practice, difficulties with soils are almost exclusively due not to soils themselves but to water contained in their voids. On a planet without any water there would have been no need for Soil Mechanics .*" It is not adequate to only see the soil from the surface, also it must be determined whether the soil classes and groundwater are changing. Clay has a great influence on the engineering behavior of soils. Clay soils are found in nature. Deposition, weathering and stresses during geological processes ensure that the natural structure is different. In geotechnical engineering, besides determining the settlement, swelling and strength properties, mineral properties of the soil, particle structure and strength must be known when clay is encountered. In this chapter, the properties of clay, the role of clay in geotechnical engineering and geotechnical studies on clay were reviewed. In this chapter, the importance and benefits of determining clay properties before building construction were determined. Consequently, clay is shown to have different properties, and it is understood that some soils behave differently. This chapter contains material drawn from different sources, as well as a literature review, and will provide available information to civil and geotechnical engineers regarding clay.

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