Displacement of Rigid Raft by the Program GEO Tools

In many practice cases, treating the raft as completely rigid is convenient. In this case, due the applied loads the raft will rotate as a rigid body. In a rigid body motion, the points on the rigid body move linearly. An analysis for the contact pressure under a rigid raft on isotopic elastic half-space medium was carried out by many authors. The oldest work for the analysis of foundation rigidity is that of Borowicka (1939). He analyzed the problem of distribution of contact stress under uniformly loaded strip and circular rigid foundation on semi-infinite elastic mass. A review about the methods of analysis of rigid rafts may be found in standards such as DIN 4018 or books as example Selvaduri (1979). Most of them were focused on the analysis of rafts on isotropic elastic half-space medium according to Boussinesq's assumption. El Gendy (2006) developed stress coefficients for triangular loaded elements and point load acting on the entire clay sub-layer through closed form equations, which may be used for any irregular shape of foundations. As an extension for the previous work, flexibility coefficients for the special cases of circular, ring piece and rectangular loaded elements are developed in this book. Using such special types of elements when analyzing rafts of regular shapes, reduces considerably the computation time required for generating flexibility coefficients comparison with using triangular loaded element. Coefficients developed in this book are used to formulate numerical and semi-analytical procedures to determine the rigid displacement under the common regular shapes of rigid rafts. Due to regular shape of foundations, contact pressure distribution at the soil-raft interface on isotopic elastic half-space soil medium can be obtained analytically. This advantage leads to reduce considerably the analysis of regular rafts, where it can be considered that half of the problem is solved.