Effect of Soil Type on Contact Stress

Abstract

This paper presents the effect of soil type on the contact stress under the footings. The soil type affects the distribution of contact stresses under footings. Several researches about the contact stresses were made with the linear elastic soil model. This model cannot take briefly the effect of soil type parameters, such as the c and φ. Therefore, the use of more realistic models is highly recommended. Elastic perfect plastic, Mohr-coulomb, model considered a good simplified non-linear model. Mohr-coulomb model was adopted to simulate the soil model using PLAXIS2D V2012. Different footings rigidities on sand and clay were studied to investigate the distribution of the contact stresses. It is investigated that, the resulted edge contact stress in sand is lower than that resulted in clay for different footings rigidities. The use of flexible footings leads to increase the contact stresses under footing center and decrease it under footing edges for the both soil types. The use of rigid footing results high contact stresses near edges and low contact stress under footing center for both soil types. These results were compatible with some investigated measurements for the contact stresses that presented in the literature. The significant result is that, the resulted distributions of contact stress on sand and clay are not compatible with the probable stresses that shown in references and standards. The cohesion of the clayey soil plays an important role for increasing the contact stress at footing edges more than that resulted in sand. It is worth to mention that, the resultants of contact stresses at edges have long arms during the calculation of the maximum bending moment at footing center. This increases the maximum moment on footings more than that calculated considering the uniform distribution of the contact stresses.