Testing the Shape of Contact Pressure Curves

The design model for a raft foundation – a loaded plate on an elastic medium predicts infinite contact stress at the edge of the raft. In practice, this increase in pressure from the central contact pressure will be limited by the strength of the underlying soil. For design purposes, it is important to know if the contact pressure under a symmetrically loaded raft foundation of constant thickness significantly increases at the edges of the raft. The purpose of the note is to establish adequate sampling schemes to study the behavior at the edges of raft by use of earth pressure cells. By making certain assumption about: 1) The accuracy of the contact pressure, as measured by earth pressure cells, and 2) the shape of the contact pressure distribution under the ratio it is possible to make recommendations as to the number and placement of earth pressure cells, so that a parameter of the contact pressure distribution is determined to within a certain degree of confidence.