Behavior of Raft Foundation Resting on Confined Sand

Construction of multi-story buildings with basement(s) in urban environment necessitates the installation of side support system including side walls for both protection of adjacent structures and for groundwater control. The side support walls are usually penetrated underneath the foundation level for different reason. The penetration of the side walls surrounding the construction excavations provides confinement of the soil underneath the foundation level. The influence of such confinement on the allowable pressure and in general the behavior of the foundation system is usually ignored during the design of the foundation system. This paper is a part of major research aiming to highlight such influence and hopefully to provide a practical tool to aid geotechnical engineer to include such influence in the design. This paper is concerned with foundations on granular soils. The paper presents numerical modelling of the problem using Finite Element method in the plain strain condition. A parametric analysis is carried utilizing this model to uncover the influence of some parameters on the behavior of raft foundations on soils under such conditions. The studied parameters include; raft width, embedded depth of the side walls and the state of denseness of the granular soils under the foundations. The depth of the foundation level is kept constant at 4m for one basement during the investigation. The results indicated that the sand confinement below the foundation level has a significant influence on the behavior of the foundation in such environment modifying the shear failure pattern under the raft and thus increasing the allowable pressure for shear failure and reducing the settlement.