Volume 27, Issue 5 (September 2004)
Effect of Presence of Rigid Base within the Soil on the Dynamic Response of Rigid Surface Foundation
The present experimental investigations study the effect of presence of rigid base at any depth within the soil mass on the dynamic response of foundation under vertical mode of vibration. Model block vibration tests on rigid surface footing are conducted on a different soil layer of finite thicknesses underlain by a rigid base. A concrete block of size 400 × 400 × 100 mm is used as the model block, and a Lazan type mechanical oscillator is used for inducing vibration in vertical direction. The finite soil layers of different thicknesses are prepared in a pit at the bottom of which a massive concrete layer of 300 mm thick was cast to represent it as a rigid base. In the investigation two different soils, namely, local in situ soil and sand are used. In total 72 tests are conducted in different loading combinations and soil types, and several important observations are reported. Two different methods are proposed to analyze the dynamic response of a foundation resting on a finite layer underlain by a rigid layer. Finally, the experimental results are compared with the results that were obtained by the proposed method. A Mass-Spring-Dashpot (MSD) model with proper consideration of damping factor is found to provide reasonably accurate results. Elastic Half Space Theory (EHST) with equivalent soil properties is found to underestimate the displacement amplitude.