比萨斜塔

这比萨斜塔in Italy is perhaps the most famous tower structure in the world, thanks to its lean (nearly5.5^0.出铅锤 -图。1) which makes it a great国际米兰national tourist attraction。当倾斜开始变得进步和过度，威胁其非常生存，岩土工程解决方案，原则上简单，即，controlled ground extraction那which was rarely attempted before, corrected the excessive tilt and stabilized it at the inclination that existed at the beginning of the 19th century, which continues to make it a tourist attraction as did theoriginal比萨斜塔。因此，练习的目的是notto correct the entire tilt and bring it to a perfectly vertical position, but to restore it to the原始倾斜，单独将使它继续成为它的吸引力。上述练习的成功标志着国际委员会的11年努力的高潮，该委员会委托了塔楼的恢复任务原始倾斜。

History of the Tilt

塔was constructed at a time when the discipline of geotechnical engineering, as it is known today, was non-existent. (Had it been constructed today, a detailed替补调查本来将在塔的设计和建造之前进行委托和开展，这将表明需要深层基础，而不是它所存在的浅基础，而是我们不会有比萨斜塔！）这个错误原来是伪装的祝福，因为这是旅游业。

这culprit in this case was the foundation soil on which was laid ashallow foundation。Hence a solution had to be sought from within the ambit of the geotechnical engineering discipline. It, however, turned out to be a common-sense solution, without much of geotechnical engineering input!

从图1看塔向南倾斜的图1。倾向，接近5.5^0.，在顶部产生近4.5米的近4.5米，相对于底线的底部边缘。

底层条件显示在图2其中可以鉴定其中三个不同的视野-A，B和C的地平线B包括主要是海洋沉积物的层B1，B2，B3和B4。塔成立于此桑迪淤泥地平线A.

这construction of the Tower started in 1173 but was suspended after five years. The 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.

它在建设的第二阶段，当其重量接近全重的三分之二时，倾向于出现。这持续到1993年，当时当局抓住了这一问题，这使得他们尝试暂时的干预措施逮捕避免结构膨胀风险的趋势。增加倾斜导致增加偏心，因此由于自身重量而增加的时刻是触发的further tiltat an increasingly快点速度。这被称为倾向于不稳定。In geotechnical engineering terms, the foundation, rather the structure itself, failed in both bearing capacity and settlement, the latter taking the form ofacute差动结算。

这modern monitoring of the Tower’s inclination started in 1911. It was found that the rate of inclination per annum increased from 76 mm in the 1940s to 152 mm in the 1980s.

When the continuing increase in inclination began to be noticed with alarm, the Government of Italy realized that unless the tilt is stopped, the consequences would be catastrophic, leading to the eventual toppling of tower itself in a few decades. Accordingly the Prime Minister appointed an ‘International Committee for the Safeguard and Stabilisation of the Leaning Tower of Pisa’. The committee which was the 17th in the long history of the monument, with Professor M. B. Jamiolkowski of the Technical University of Torino, Italy, in the chair, was a多学科来自广谱的专家，包括中世纪艺术，考古学，建筑石头，建筑，结构工程和岩土工程历史的专家。

Final Measure of Stabilization

经过多次初步尝试，选择校正塔倾斜的最终措施是从塔北部的地平线A的下部逐渐提取土壤。这项措施已经提到于1962年。它成功地在1992年成功应用，以减轻墨西哥城大教堂遭受的非常大的差异定居点的影响。通过相同的，数值分析，进行离心机和大规模场试验中的物理模型研究，证明了该方法的可行性。

最终的计划'在挖掘下'被说明图3.。Forty-one inclined boreholes were drilled on the northern side starting with guide tubes fixed on an R.C. beam. Extraction was carried out using helical augers.

本练习的目的是在1800秒的弧度下减少塔的倾向（1度弧= 3600秒的弧）。这项工作开始于21-2-2000，并于19-1-2001停止，当时的土壤总量达到37米^3.并且倾斜度降低到近1620秒的弧。塔继续its rotation northwards and in July 2001 the total reduction in inclination reached 1842 sec. which corresponded to a reduction of 446 mm of the overhang which was 1/10th of the value ofHFig.49.1) recorded in 1993. It is significant that, apart fromground extraction那no steps were undertaken to stabilize the foundation soil with a view to ensuring long term performance. In Dec. 2001, when all the related works were over, the Committee ‘returned’ the Tower to the Italian Government, with a request to carefullymonitor下一个结构十年，将窗帘敲打在巨大的任务上，就像之前没有见证一样。

Article written by

Dr. Nainan P. Kurian