The leaning tower of Pisa is a one of Italy’s most famous tourist attractions. Saved from collapsing at the turn of the millennium, it now safely awaits visitors from around the world. The same cannot be said for the Garisenda Tower in Bologna, which is currently leaning more than the one in Pisa and is at high risk of collapse. However, Italian authorities and scientists analysing the state of the building have found that they can use the exact same system that saved the Pisa Tower on Garisenda.
Standing next to the taller Asinelli Tower, Garisenda, similarly to the Pisa Tower, started off on the wrong foot from the beginning. It was not time or erosion or natural elements that led to its leaning, rather poor structural planning. Built in the 12th century, the tower was initially supposed to be 60 metres tall, but since the ground was already caving under its weight during construction, it was topped at just 48 metres.
By the 14th century, the tower’s incline was already famous and an attraction. Dante Alighieri mentioned it in his renowned “Divine Comedy”, while Giosuè Carducci dedicated a poem in his “Barbarian Odes” to the Two Towers of Bologna (Garisenda and Asinelli). Today, Garisenda slopes at a 4° angle, just slightly over the Pisa tower’s 3.9° angle.
Last year, the streets around the two towers were closed for inspections to be carried out on the tower’s state by a group of experts appointed by the Municipality of Bologna, made of professors, architects and engineers. They concluded that the tower was at “high risk” of collapsing. Fortunately, they found that the system used on the tower of Pisa could also save Garisenda.
The pylons supporting the Tower of Pisa are still available in the area of the Opera Primaziale Pisana and have been maintained until 2019. They consist of two large trestles, anchored to the foundation with a system of poles that anchor into the ground at a depth of 30 meters. The pylons will be de-rusted where needed and transported to Bologna, where a three phase process will begin.
Ecco come sarà messa in sicurezza la #Garisenda: useremo i tralicci impiegati sulla Torre di Pisa. La soluzione consente così di accorciare i tempi e i costi. L’intervento avverrà in 3 fasi distinte. Scopri i dettagli dell'intervento 👉 https://t.co/B2KDeqAiy4 #Bologna pic.twitter.com/crRMDwt2eq
— Comune di Bologna (@comunebologna) March 28, 2024
In the first step, two contrast pylons will be positioned, with the role of passive protection in order to operate safely at the base of the tower. Once in place, a pair of cables will be tensioned only to strengthen the system, with no significant counterthrust applied at this stage. Then, the masonry of the building will be improved by traditional consolidation interventions, such as injecting a hydraulic lime-based mortar mixture compatible with the one the tower is made of into its foundation. In the last phase, the success of the process will be analysed and the tension in the cables will be reduced to reduce the stress on the tower’s base.
The aim of the project, earmarked at €19 million, is not to completely strengthen Garisenda, but keep its incline while consolidating its foundation and ensuring it can remain safely standing. If everything goes well, the municipality estimates to have the pylon system in place by the end of the year, with “further consolidation and restoration work, which still needs to be planned” to take place in 2025 and 2026, according to Bologna Mayor Matteo Lepore.
