ABOUT LEANING TOWER OF PISA – HISTORY OF TILT & RESTORATION

Figure 1 Leaning Tower of Pisa
Figure 1 Leaning Tower of Pisa

Tower of Pisa Italy probably has the most famous tower structure in the world, due to its lean (approx.) 5.50 out of plumb – Figure 1) which makes it a great international tourist attractions, When lean began to become progressive and excessive, threatening its existence, a geotechnical engineering solution was, in principle, simple, that is, controlled ground extraction, What was seldom attempted before, corrected the excessive inclination and stabilized it on an existing inclination in the early 19th century, which continues to be a tourist attraction. Original Tower of Pisa. Therefore, the aim of the exercise was No To fix the entire tilt and bring it to a perfectly vertical position, but to restore it original inclination, which alone would make it the attraction that it was. The success of the above exercise marked the culmination of an 11-year effort by the International Committee, which was tasked with the restoration of the tower. original inclination,

history of tilto

Figure-2 Soil Profile at Tower Site
Figure-2 Soil Profile at Tower Site

The tower was built at a time when the discipline of geotechnical engineering, as it is known today, was non-existent. (If it had been built today, a detailed description sub-soil investigation The tower would have been and will have been commissioned before the design and construction, indicating the need for a deep foundation rather than a shallow foundation, but then we would not have had the Leaning Tower of Pisa!) This error was disguised for the tourism industry. proved to be a boon.

The culprit in this case was the soil of the foundation on which was laid shallow foundation, Therefore a solution had to be sought from within the scope of the geotechnical engineering discipline. However, without geotechnical engineering input, it turned out to be a common sense solution!

It can be seen from Figure-1 that the tower is inclined towards the south. Tilt, about 5.50 , creates an overhang of about 4.5 m at the top with respect to the bottom edge of the plinth.

Shown in subsoil condition line drawing number 2 In which three distinct horizons – A, B and C can be identified, of which Horizon B consists of layers B1, B2, B3 and B4 which are mostly marine deposits. was installed in the tower sandy silt horizon A layer

The construction of the tower began in 1173 but was suspended after five years. Construction was resumed in 1272 and in six years the tower was brought to its top seventh cornice. To this was added the bell chamber at the top which was completed in 1370.

During the second phase of construction, when its weight approached close to two-thirds of its full weight, the tilt began to appear. This continued until 1993 when the authorities were made aware of the problem that forced them to try Temporary Intervention to prevent the tendency to avert the risk of collapse of the structure. Increasing inclination increased eccentricity and consequently increased moment due to own weight which triggers lean forward with speed faster Rate. it was referred to as tilt instability. In the context of geotechnical engineering, the foundation, but also the structure itself, failed in both bearing capacity and settlement, taking the latter form Intense differential settlement.

Modern monitoring of the tower’s inclination began in 1911. It was found that the rate of inclination per year increased from 76 mm in the 1940s to 152 mm in the 1980s.

When the continued increase in tilt was viewed with alarm, the Italian government realized that unless the tilt was stopped, the consequences would be disastrous, with the tower itself falling in a few decades. Accordingly the Prime Minister appointed the ‘International Committee for the Security and Stabilization of the Leaning Tower of Pisa’. The committee, which was the 17th in the monument’s long history, was chaired by Professor MB Jamiclowski of the Technical University of Torino, Italy, was multi disciplinary Body with experts drawn from a wide spectrum, including the history of medieval art, archaeology, construction stones, architecture, structural engineering and geotechnical engineering.


last resort of stabilization

quarrying under fig-3 scheme
quarrying under fig-3 scheme

After several initial attempts, the gradual extraction of soil from the lower portion of Horizon A on the northern side of the tower was the last resort to correct the chosen tower’s inclination. This measure was suggested only in 1962. It was successfully implemented in 1992 to reduce the impact of the very large inter-settlements suffered by the Metropolitan Cathedral of Mexico City. Encouraged by the same, numerical analysis, physical model studies in centrifuges and large-scale field trials were conducted which proved the feasibility of the approach.

the final plan ofunder digging‘ is shown in Fig-3, Forty inclined boreholes were drilled in the north direction starting from the guide tubes fixed on the RC beams. Extraction was performed using a helical auger.

The aim of this exercise was to reduce the inclination of the tower to an arc of 1,800 seconds (1 degree of arc = 3600 seconds of arc). The work was started on 21-2-2000 and stopped on 19-1-2001 when the total extruded volume of soil reached 37 m3 And the inclination was reduced to an arc of about 1620 seconds. Tower Continuous It rotated northwards and in July 2001 the total decrease in inclination reached 1842 s. which corresponded to a reduction of 446 mm of overhang which was 1/10th of the value of K h Fig.49.1) was recorded in 1993. It is important that, in addition to land extractionNo steps were taken to stabilize the foundation soil to ensure long term performance. In December 2001, when all related work was finished, the committee ‘returned’ the tower to the Italian government, with a careful request. Monitor structure for the next ten years, to cover a gigantic task that has never been seen before.

article written by

Dr. Nain P. Kurien

Er. Mukesh Kumar

Photo of author
Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.