In many practical cases, it becomes important to study the interaction of elastic or rigid foundations, which are constructed simultaneously. In this case, there will be interaction of foundations due to the overlapping of stresses through the soil medium, however the structures are not statically connected. The interaction of foundations will cause additional settlements under all foundations. The conventional solution of this problem assumes that the contact pressure of the foundation is known and distributed linearly on the bottom of it. Accordingly, the soil settlements due to the system of foundations can be easily determined. This assumption may be correct for small foundations, but for big foundations, it is preferred to analysis the foundation as a plate resting on either elastic springs (Winkler’s model) or continuum model. In spite of the simplicity of the first model in application, one cannot consider the effect of neighboring foundations or the influence of additional exterior loads. Thus, because Winkler’s model is based on the contact pressure at any point on the bottom of the foundation is proportional to the deflection at that point, independent of the deflections at the other points. Representation of soil as Continuum model (methodes 4, 5, 6, 7 and 8) enables one to consider the effect of external loads.

The study of interaction between a foundation and another neighboring foundation or an external load has been considered by several authors. Stark (1990) presented an example for the interaction between two rafts. Kany (1972) presented an analysis of a system of rigid foundations. In addition, he presented a solution of system of foundations considering the rigidity of the superstructure using a direct method (Kany 1977). Recently, Kany/ El Gendy (1997) and (1999) presented an analysis of system of elastic or rigid foundations on irregular subsoil model using an iterative procedure.

This section presents a general solution for the analysis of system of foundations, elastic or rigid, using the iterative procedure of Kany/ El Gendy (1997) and (1999).

A swimming pool is supposed to be constructed at a river. The existing ground around the pool has to be increased up to a meter. The pool has dimensions of 25 [m] * 10 [m] and maximum water depth of 1.20 [m] as shown in Figure (4.32). The foundation level is 1.45 [m] under the ground surface. Slab and walls are reinforced concrete of concrete grade B 25 with thickness of 25 [cm] for slab and 20 [cm] for walls. It is divided into two independent parts through a joint at the pool middle.

The filling material around the pool is noncohesive soil (Figures (4.33) and (4.34)). The filling is supposed to be carried out after finishing the pool.

In this example, it is required to study the following:

i) Influence of the joint on the settlements, contact pressures and internal forces of the pool slab and the pool walls in case of the pool is completely filled by water.

ii) Influence of the ground rising by additional filling soil material at the southern part of the pool on the settlement.