BEHAVIOUR OF REINFORCED SAND UNDER LIQUEFACTION

Abstract

One of the major cause of catastrophic damage,to structures during the earthquakes, has been liquefaction of loose and saturated cohesionless soil deposits. Structures resting on such deposits,may experience large scale tilt, movements and damages, due to the liquefaction of the foundation soil material, resulting into loss of valuable life and property. The analysis and mechanism of liquefaction, has been well developed. But, there is a need for research, on control of liquefaction. The proposed investigation aims to study the performance of NETLON GEOGRID, to control the liquefaction. The study has been extended to the use of Horizontal Filter and Vertical Drains of Gravel, to stabilize a potentially liquefiable soil deposit. These investigations have been carried out, without imposing any surcharge load. In the proposed investigations, fine locally available SOLANI SAND deposited in a test tank 1.05 m x .6m x .6m and subjected to sinusoidal vibration, has been used. Netlon Geogrid, Horizontal Filter and Vertical Drains, of Gravel passing 6 mm sieve and retained on 4 mm sieve, have been tried to control liquefaction. Netlon, at two different horizontal spacing of 5 cm and 10 cm,Alas'. been tested. Vertical drains of 5 cm diameter (d), at three different spacing of 2.5d, 3d and 4d have been employed. The frequency of the vibrations, has been fixed at 4 cps. The acceleration range being from 10%g to 40%g. The relative density (initial) of 20% has been maintained for"all the tests. Three piezometers of rigid steel pipe extending into the centre of the tank, have been installed at three different depths of 8, 19, and 26 cm, from the base of the tank. PVC tube and a manometer graph, have been used, to study the rise and fall of dynamic pore water pressure. Based on the study, it is observed that Netlon Geogrid can control liquefaction. But more effective method, to reduce the liquefaction potential, is by providing Horizontal Filter and Vertical Drains of gravel. Drains of 5 cm size, with a spacing of (iii) three times its diameter, being most effective method, in controlling the liquefaction. However, further parameteric studies are required using a larger test tank and changing initial relative density of the deposit.