Determination of Diameter of Belled Shafts with respect to Uplift Forces Resulted From Expansive Soil Layer in Active Zone

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.