A New Technique to Avoid Tilting Problems During Liquefaction

Abstract

Soil liquefaction is one of the primary concerns during construction of foundations on saturated sand in seismically active areas. Seismically induced settlement and tilting of structures due to the liquefaction have resulted in detrimental consequences. The generation of excess pore pressure is the key to the initiation of liquefaction which mainly occurs due to an earthquake. A series of measures have been tried over time to time to mitigate the effects of liquefaction but till now no effective measure has been evolved to safe a structure founded on a liquefiable soil. The present paper covers an experimental study on a two-storeyed frame structure standing on liquefiable soil to show its performance soon after liquefaction. The shape of the footing is changed from conventional to non-conventional footing. Two non-conventional shapes adopted in this study are spherical and trapezoidal in cross section, designed in such a way that they achieve stable equilibrium under both vertical loads and upthrust generated due to pore water pressure generation during liquefaction. Series of tests were performed with conventional rectangular footing, spherical-shaped footing and trapezoidal-shaped footing on a one-dimensional shaker at frequencies from 1 to 5 Hz. Accelerations of the tank were compared with the accelerations imposed over the footings. Displacements were measured from a fixed point using a ruler scale, and tilt was measured from comparison of photographs taken before and after shaking from a stationary point. It was observed that the vibrations at upper floors are more for conventional footing while vibrations at footing level are more for modified footings. It was also observed that the modified footings floated over the liquefied sand for a longer time and then sank instead of being tilted. The paper concludes that spherical-shaped footing is the best alternative to eliminate the tilting problem.