DYNAMIC RESPONSE OF EMBEDDED BLOCK FOUNDATION

Abstract

The prediction of the response to the dynamic force is of major importance for the design of footings exposed to dynamic effects. The theory of surface footings greatly overestimates the real response and neglects the fact that footings are founded beneath the surface of the ground i.e., partly embedded. It has been recognized for many years that the vibrations of footings can be greatly effected by the partial embedment into the soil. Nevertheless very little quantitative information is available because of the difficulties associated with a rigorous theoretical solution and with the generation of the experimental findings. Here, efforts have been made to present a report on experimental investigations carried out on massive blocks, attempting to create a perfect homogenous half space. The experiments were carried out in a wooden tank. Saw dust filled in gunny bags were nailed to the surfaces of the tank of size 1700mmxl300mmx1400mm high on all four sides and also at the bottom to get the advantage of absorption of the waves coming on to the hard wooden surface. Three concrete blocks of sizes 800mmx400mmx400mm high, 800mmx400mmx570mm high and 800mmx400mmx670mm high were used to carryout the experimentation in both vertical and horizontal modes of vibration. The blocks were instrumented with frequency and amplitude measurement devices. Study has been carried out on the effect of influencing parameters (considered here) viz, embedment ratio, excitation force level and mass of the (i) foundation block on the response parameters viz, resonant amplitude, resonant frequency, damping ratio and coefficient of elastic uniform compression / shear