Numerical Analysis for Prediction of Shallow Foundation Settlement Based on Plate Load Test Results

Prediction of settlement and its distribution for shallow foundation which are among the most important problems for geotechnical engineers are influenced by various factors such as shape and stiffness of foundation, geometry, weight and stiffness of structure, type, stiffness, stress-strain history and thickness of soil layers. In the literature, there are different classical relationships for prediction of foundation settlement. These relationships are generally based on elasticity theory for immediate settlement and oedometric conditions for time-dependent settlement. Due to the limitation in consideration of material behavior, geometry and boundary conditions and loading, related to these relationships, application of calculation codes with proper constitutive model can be regarded as a satisfactory method. In this paper, a set of finite element analyses using an elastoplastic soil model have been performed for prediction of shallow foundation settlement and its distribution. Distinguished aspect of these analyses is that the soil constitutive model has been calibrated using Plate Load Test results. Similarity of stress-strain field for the Plate Load Test and real foundation, on one part, and the proper relationship between elastic and hardening modulus of constitutive model and confining stress, on the other part, led to enriching the results of prediction qualitatively and quantitatively. Using the calculation code (Plaxis 3D) calibrated based on Plate Load Test, the effects of foundation width and depth on settlement and its distribution were studied. Besides, classical relationships of settlement estimation were evaluated by comparison with numerical results. The obtained results indicate that, firstly, the dependence of foundation settlement to width is significantly nonlinear, so existing classical relationships don’t consider this important aspect. Settlement distribution depends on soil and footing stiffness. In the case of granular soils due to significant dependence of elastic and plastic modulus to confining stress, settlement in foundation edge is more than center. The results of analyses also indicated that settlement and its distribution depend nonlinearly on foundation depth. Based on settlement distribution of foundation, it was found that sub grade reaction modulus is not a constant parameter for a given problem. On the other hand, settlement distribution dictates the sub grade reaction modulus distribution for foundation analysis and design.