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The lime column (LC) technique has been commonly used for the improvement of expansive soils. The achievement of this technique depends on the lime diffusion into the expansive soils, but lime diffusion into the expansive soil is generally a slow process due to the low permeability of these soils. In this study, sodium lignosulfonate, which is used as a superplasticizer in the concrete industry, was added to lime columns to accelerate the diffusion of lime particles. First, treated expansive clay specimens with thirty-seven 4.5 mm diameter columns were prepared in an oedometer ring. These columns were filled with two different mixtures: water-lime and water-lime-sodium lignosulphonate to investigate the effect of the addition of sodium lignosulphonate. Free swell tests were done on these treated expansive clay specimens that were subjected to different curing periods, it was observed that the treated specimens with sodium lignosulphonate lime columns (NaLS-LC) are more effective than the treated specimens with lime columns (LC). A treated expansive clay specimen (in a 30cmx30cm mold) with seven pieces of 45 mm diameter sodium lignosulphonate lime columns were prepared to observe the alteration of engineering properties of untreated expansive clay specimen (US) located between the columns. Free swell and unconfined compressive strength tests were done on the undisturbed expansive clay specimens taken from the mold between the columns. SEM-EDX analyses were made to investigate whether the ettringite mineral, which leads to swelling of the expansive soil during lime stabilization, forms or not. While the ettringite mineral formed during the curing period in the lime column stabilization method, the addition of sodium lignosulphonate to lime columns blocked the formation of the ettringite mineral. It can be stated that sodium lignosulphonate lime columns (NaLS-LC) show better performance than lime columns (LC), in the treatment of expansive clays.

Expansive soils are found in many parts of the world that are especially arid and semi-arid regions. They have caused several damages of lightweight structures for decades. For this reason, a more suitable foundation type should be selected and designed for the lightweight structures built on these soils. For example, the application of belled shaft foundation at expansive soil layer is preferable method in practice. However, one of the worst cases at the design of this foundation is accepted that the swelling of expansive soil placed in active zone. Therefore, this condition should be taken into account at the design process of this foundation. In this study, the diameter of belled shaft was separately determined with respect to some factors such as the diameter of shaft, the depth of active zone, the friction angle between shaft and soil, and the ratio between the undrained cohesion of soil at stable zone and the swelling pressure of expansive soil placed in active zone. In the calculation process, four different shaft diameters that are 0.3 m, 0. 45 m, 0.60 m, and 0.75 m were utilized. Also the depth of active zone that started from 1.5 m to 15 m was specified. To sum up, the optimum shaft diameter was found as 0.45 m.

The settlements occurred in building foundations depend on many soil parameters. Thus, these parameters make the solution both difficult and complex during the calculating process. Therefore, finite element programs use the subgrade reaction coefficient to facilitate the foundation solution. Two different methods, which are Winkler method and Pseudo coupled method, are used in the basic solutions with the coefficient of subgrade reaction. While the Winkler method can be solved with a single field, the pseudo method can be solved with 2 or more fields. In this study, a 10 story building with a 36 m x 36 m square foundation was separately designed on four different sand soils. Two of these soils are classified as C and the others are classified as D according to Eurocode 8. The foundation of this building built on four different soils was divided into six different areas (one region, two regions, three regions, five regions, seven regions, 10 regions). Consequently, 24 pieces analyzes were solved with ETABS programs. One of the results from these analyzes is that Winkler method is suitable for the rigid foundation. In addition, since the settlements occurred at raft foundations are small, it has been observed that both Winkler and Pseudo-coupled method are suitable for rigid foundation acceptance. Pseudo-coupled method has generally been found to be a suitable method for flexible raft foundation. In the Pseudo-coupled method, the highest settlements were obtained in the two-region solutions. An optimum number of fields was found to be 7 for Pseudo-coupled method.