Stability of Leaning Towers

Abstract

The Leaning Tower of Pisa has intrigued soil mechanicians for many years as to why it tilted in the first place. The more urgent question is, however, whether it is safe today against complete collapse. Methods available in the literature concern the stability of initially vertical towers, not tilted towers, and even for the former there exist very little physical data in verification. The centrifuge is used here to make model tests on towers having small initial tilt and to determine the critical height of tower that causes instability. Two new approaches are presented that give close correlation with experimental results. These approaches are based upon: (1) The experimental determination of rotational stiffness of the soil foundation system; and (2) a method analogous to that proposed by Southwell (1932) for predicting the stability of imperfect columns.