Natural Base Isolation System for Earthquake Protection

The performance of a well-designed layer of sand, geo-grid, geo-textiles and composites like layer of sand mixed with shredded tyre (rubber) as low-cost base isolators is studied in shake table tests in the laboratory. The building foundation is modelled by a 200 mm × 200 mm and 40 mm thick, rigid plexi-glass block. The block is placed in the middle of a 1 m × 1 m tank filled with sand. The selected base isolator is placed between the block and the sand foundation. Accelerometers are placed on top of the footing and foundation sand layer. The displacement of the footing is also measured by transducers. The whole set-up is mounted on the shake table and subjected to sinusoidal motion with varying amplitude and frequency. Sand is found to be effective only at very high amplitude (>0.65 g) of motion. Among all the different materials tested, the performance of a composite consisting of sand and 50% shredded rubber tyre placed under the footing is found to be the most promising as a low-cost, effective base isolator.