LIQUEFACTION BEHAVIOUR OF SANDS DURING VIBRATIONS

Abstract

Liquefaction of saturated sand has often been main cause of the catastrophic damage to structures resulting in loss of life and property. During liquefaction structure resting on saturated and experienced large settlements and tilts. The buried structures like septic tank, manhole,wooden piles etc. floated up. The extra precaution taken in design of superstructure would not be of any help during the earthquake. Thus it is necessary to determine possibility of liquefaction at the site before the construction. activity starts and suitable measures should be adopted to prevent damages due to liquefaction. For prediction of liquefaction possibility two type of laboratory tests are in practice (i) triaxial shear tests on small samples and (ii) vibration table tests on large samples. In triaxial testing on small samples various investigators have observed that liquefaction can occur even at high relative densities. This is anomalous to known behaviour of dense sand. Thus triaxial test data seems to be in error, this may be due to redistribution of void which is not representative of field behaviour. Thus for prediction of liquefaction behaviour of dense sand under different surcharge pressure, vibration table studies were carried out. In present investigation a sand sample of 1.05m X 0.60m X 0.32m deep was prepared in vibration table. Steady state vibrations of desired acceleration and frequency can be imparted to soil sample prepared in table. Effect of three variables was studied (i) Acceleration (ii) Relative density (iii) Surcharge pressure. V1 In present investigation through extensive tests some of the earlier findings were confirmed but its main finding is that dense sands may not liquefy during an earthquake. Therefore triaxial test data on small samples which appear to be in error should be used with due care for determining liquefaction possibility of a site, vi