ABSTRACT
LEANING TOWER OF PISA Cathedral bell tower, 58 m high, 4 m out of vertical weighs 14 0001; imposed 500 kPa on clay with ABP -50 kPa. Main settlement is due to compaction and deformation of soft clay at depth of 11-22 m. Differential movement probably started due to clay variation within overlying silt layer; subsequently it was due to eccentric loading. Stabilization in 1993-2001 was by controlled induced subsidence of north side. Temporary counter-weight, of 600 t of lead, tilted tower back 15 mm. Creep closure of 41 uncased boreholes, each 225 mm in diameter, with repeated drilling to remove a total of 35 m 3 of soil, tilted the tower back another 425 mm; so it is now stable. Cable bracing was just for security during drilling. Temporary tendons confined masonry to reduce risk of bursting failure until load was reduced by tilt reduction.
