S C I E N T I F I C
A M E R I C A N
|
|
February 1929 S C I E N T I F I C A M E R I C A N |
 WHERE GALILEO TRIUMPHED Here the famous experiment on the relative rate of descent of falling bodies took place | For centuries the famous Leaning Tower of Pisa has been sinking vertically into the soft river valley sediments on which it rests, at the average rate of a millimeter a year. That long continued process is now about to be brought to an abrupt and permanent stop. If the present plans of the Italian government are carried out as vigorously as work has already been begun, the ancient tower, which has stood on a poor foundation since A. D. 1174, when its construction was started, will soon be equipped with a broad, secure footing. Yet the structure itself will not have been moved an inch in the process, either up or down or sidewise. |
|
EMPHATICALLY the Leaning Tower is not to be straightened up. While a restoration to the intended vertical, doing away with its 14 feet of inclination in a total height of 178 feet, might make appeal to the severely practical minded, yet it would also do violence to the sentiments long connected with this historic structure. There are many other beautiful campaniles in the world but there is only one Leaning Tower of Pisa.
The plan which will be pursued, short of some unanticipated discovery which might conceivably alter it, is to inject cement in liquid form through pipes inserted under the Tower, by one of the well-known cementation processes which are now being employed in certain kinds of engineering work where direct access is difficult or impossible. This work will doubtless be performed by the firm which is at present carrying on preliminary experiments at the site of the Tower; the same firm, in fact, which is at present safeguarding St. Paul's Cathedral in London by cement injection, as previously described in the SCIENTIFIC AMERICAN. |
 WHAT IS UNDER THE TOWER? A core drilling machine projects above the temporary enclosure. Here samples of the sand and clay beneath the Tower were taken | Late last autumn when the operations at Pisa were inspected, a most interesting large-scale test experiment was found to be in progress. Instead of proceeding directly with the injection of cement under the priceless Tower, an operation whose complete success would possibly be problematical, the Commissione Ministeriale per la Torre di Pisa of the Italian government has let to the |
|
Francois Cementation Company,Ltd., of Doncaster, England, the contract to carry out a series of preliminary experiments upon the soil at spots to be chosen as near the Tower as can be tested without involving direct risk to it. These experiments should provide valuable and exact data concerning the bearing resistance of the various strata of sand and clay in the neighborhood and to a considerable depth. These data will include the pressure at which the cement can be injected into the ground; the quantity of cement the ground will take; the increased bearing resistance obtained; the condition of the treated ground after varying intervals of time; unit factors of time and cost; information as to the best sequence of operations; depths of injection, and so on.
The large scale experiment partly shown in one of the illustrations will be duplicated on a number of plots within a like radius from the Tower. Finally, and in the light of the experience gained by the experiments, the soil directly under the Tower itself will be tenderly and cautiously operated upon. At the time mentioned, one small job was nevertheless taking place directly under the Tower. This, however, had nothing immediate to do with the repair of its foundations, but consisted, rather, in the careful extraction of sample cores of earth four inches in diameter and several fathoms in length. The sampling equipment shown within an enclosure in one of the illustrations, was set up successively on each of the four sectors immediately adjacent to the Tower and cores were taken in an inward slanting direction, thus providing samples from beneath it. These cores, it is of interest to note, do not agree closely in stratification with other cores made only 200 feet from the Tower. |
 PART OF A TEST EXPERIMENT A hose line may be seen connected to one of the vertical pipes. Nearby were cement mixers and heavy pumps for injecting cement |
This is not surprising, as the various strata of sand and clay in the entire neighborhood represent river estuary deposits and such strata are apt to vary quite radically in nature, within short distances. This emphasizes and confirms the need of making a whole series of test experiments as described, in order to insure success. |
|
Leaning Tower of Pisa Information Leaning Tower of Pisa History Leaning Tower of Pisa News Leaning Tower of Pisa Web Links Leaning Tower of Pisa Humor Leaning Tower of Pisa Gallery |