Evaluation of Ultimate Bearing Capacity and Influence Zone of Clay Using FEM: A Comparison with Theoretical Models

This research aims to evaluate the ultimate bearing capacity of soft clay soil and indicate the form of the failure surface and the influence zone under a square foundation by utilizing the finite element method. A square foundation resting on a layer of clayey soil has been studied. The engineering characteristics of the clay soil have been retrieved from site investigation reports for the school project executed in Naseriyah. Seven groups of data have been used for seven cases of projects with a range of undrained cohesion of about 31 to 51 kPa. The clay soil was modeled as a Mohr-Coulomb in the finite element analysis and subjected to a uniform distributed load at the center of the studied area. The dimensions of the soil under the foundation have been selected so that the stresses at the boundary vanishes. The results of finite elements were compared with five theoretical equations Prandtl’s, Terzaghi’s, Meyerhof’s, Hansen and Vesic’s. It is concluded that (a) the results of finite element agreed with results obtained by Meyrhof equation and the error percent was 7%, then Hansen and Vesic with a percent of 8% while Terzaghi and Prandtle were not agreed with a percent of about 15%. (b) The dimensions of boundaries of the failure surface beneath a rigid strip footing submit to a centric vertical load and the depth ofthe failure zone is approximately equal to 1.15B.