EFFECT OF EMBEDMENT AND GEOGRID REINFORCEMENT ON DYNAMIC ELASTIC PROPERTIES OF SILTY SAND

Abstract

The dynamic properties of soils are required for analyzing machine foundations, and substructures subjected to earthquake. During the past three decades, reinforced earth has been extensively used to improve the static strength characteristics of soils The study of dynamic response of foundation on reinforced sand beds and the dynamic properties, has not received much attention. It has been recognized for many years that the vibration of footing is affected by its embedment into the foundation soil. The present thesis work has been carried out to study the dynamic response of foundation on unreinforced and reinforced sand beds experimentally and to interpret the dynamic properties of reinforced sand on the basis of experimental data. It is anticipated that the study would help in better understanding of the dynamic behaviour of foundations on reinforced sand beds and lead to realistic and safe design. A block vibration test is generally used for the determination of dynamic stiffness properties of soils. A large number of reinforcement parameters are likely to influence the dynamic behaviour of soil: the present study, however, has been undertaken to investigate the following aspects. Efforts have been made to present a report on experimental investigation carried out on model concrete block. The experimental investigation consists of performing vertical block vibration tests (total number 36) on unreinforced and reinforced sand beds with evaluation of embedment effect. A masonry test tank of size 1600mmxl200mmxl200mm high was used to prepare the sand beds reinforced with 2 to 4 geogrid layers. An M-20 concrete block of size 800mmx400mmx400mm high was used to carryout the experiments in vertical mode of vibration. The frequency and acceleration observations were recorded at three different force levels. The block was instrumented with frequency and acceleration measurement devices. The study has been carried out on the effect of influencing parameters (considered here) viz, embedment ratio, excitation force level and number of reinforcement layers on the response parameters viz, resonant amplitude, resonant frequency, damping ratio, coefficient of elastic uniform compression, elastic modulus and shear modulus. The results of this study are especially useful in the design of foundations of machines, where the natural frequency of the soil-foundation system may lie close to the operating frequency of machine and the maximum amplitude is likely to the exceed permissible limits. iii The maximum amplitudes can be brought under control and the disturbance during the starting and stopping stages of the machine can be reduced. lv