1934 stabilization attempt backfires

In 1934, engineers drilled 361 holes in the foundation of the Leaning Tower of Pisa to inject cement and realign it. This effort, initiated under Mussolini, resulted in the tower leaning further, despite its intended purpose of stabilization.

Discrepancies in inclination measurements

A South African civil engineering journal reported the tower gained 33 seconds of arc in inclination in one year, while PBS NOVA mentions approximately 360 seconds of arc added. The estimates do not agree on the exact magnitude, only on the direction.

Successful realignment in 1998–2001

A gradual removal of soil under the northern side realigned the tower between 1998 and 2001. The inclination was fixed at 3.97 degrees, intentionally not corrected. Today, the tower leans approximately 4 degrees toward the south, a displacement of slightly less than 4 meters from the vertical.

Earlier actions worsened the tilt

Before Mussolini, an architect had already worsened the inclination by pumping water out from under the tower. The 1934 project followed an intuitive logic: drill 361 holes, inject cement, and rely on this new base to stabilize the structure. However, the remedy worsened the tower’s condition.

Soil and water contribute to instability

Under the tower, there is no rock: clay and silt, deposited by an ancient estuary. This soft soil settles under the load, and engineer John Burland compares the situation to children building a tower of bricks on a thick carpet. The 1934 injection disturbed the foundation, and the tower leaned a little more. Water also plays a role, as the groundwater table is only about 2 meters below the surface.

Drainage system and visitor numbers

Variations in groundwater levels worsened the inclination, which led the team to install a drainage system. Closed to the public in 1990, the tower received 700,000 visitors per year. An international committee was formed the same year, as the inclination had reached a point where the tower was on the verge of falling.

Lead ingots and final stabilization

In 1995, 600 tons of lead ingots were placed on the northern side. This lead did not correct anything but kept the tower in its current state while the team prepared the real intervention. The final stabilization involved removing soil from under the northern side, which is the highest. The tower stabilized at an inclination of 3.97 degrees, intentionally retaining the angle as part of its cultural heritage.