The Mexico Earthquake of September 19,1985—Deformability of Mexico City Hard Deposits under Cyclic Loading

Abstract

Buildings founded on point bearing piles performed better than those founded on friction piles in Mexico City during the earthquakes of September 19 and 20, 1985. Nevertheless a few buildings supported on end bearing piles tilted considerably after the earthquakes. Friction piles have been preferred over end bearing piles in Mexico City because the latter type of foundation has drawbacks resulting from the apparent emersion of structures brought about by regional subsidence. Experimental research into the behavior of the soils that form the bearing strata for pile tips shows that stress path testing can be used to obtain a deformability parameter which allows for the calculation of permanent deformations induced by earthquake loading below end bearing piles. The tests indicate that the deformability of these soils under cyclic loading is rather low. The use of the deformability parameter is illustrated by means of an example which shows that the behavior predicted on the basis of stress path testing and a simplified deformation analysis is consistent with observed field performance.