Influence of rigid base on damping of finite sand stratum

Abstract

Vertical vibration tests were conducted using model footings of different size and mass resting on the surface of a finite sand layer with different height-to-width ratios underlain by either a rigid concrete base or a natural red-earth base. Comparison of the results of the experimental study showed that the rigidity of the finite base has a significant influence on the damping ratio of the foundation–soil system. The damping ratio of the finite sand stratum underlain by the rigid concrete base is significantly lower than that obtained for the finite sand stratum underlain by the natural red-earth base. The damping ratio in both cases is less than 10%, suggesting that only material damping predominates. Comparison of the predicted damping ratio for a homogeneous sand stratum with the experimental damping ratio obtained corresponding to the height-to-width ratio of 3 of the finite sand stratum underlain by either the rigid concrete base or natural red-earth base indicated a significant reduction in damping ratio of the foundation–soil system, irrespective of the contact area and mass ratio of the model footing.