Geoscience Reference
In-Depth Information
Towers were not only a city's pride but also for rich and mighty families. The
Tower of Pisa is probably the best known. The construction of it is characteristic
and the consequences are characteristic for many such towers.
5
Also in Holland so
many towers were erected. The foundation usually consists of a raft of heavy
wooden beams placed just under groundwater level (Fig 1.6a), packed in manure
(conservation). Sometimes a ground improvement was applied, particularly
suitable for soft soils (see Fig 13.10). The construction process advanced slowly,
and unavoidable settlements did not cause damage worth mentioning in the
masonry, because the mortar of that time contained chalk and could follow slow
deformations (creep). Differential settlements did however cause inclinations,
which could hardly be avoided. Holland counts more than 50 oblique towers (Fig
1.6b), some of which collapsed and a few of which have been successfully put
straight (Montelbaan Tower in Amsterdam in 1610, the Lawrence Church tower in
Rotterdam in 1654, and the church tower of Nijland in 1866).
Fascinating is the construction of a 60 metre deep water well in Orvieto (Italy).
The well has a double wall with in between a spiral staircase. Etruscans used to
build their settlements on mountaintops for protection and therefore needed deep-
water wells for water provision, in particular during siege.
Around 1650, the Taj Mahal was built ordered by Mughal emperor Shah Jahan
for his beloved wife Mumtaz Mahal, who died in 1631 at the birth of her 14
th
child.
The foundation of this huge monument, partly erected with white marble decorated
with marvellous branded motifs of semiprecious stone, in perfect symmetry, is very
competently based on cylindrical wells. An area of roughly three acres in the soft
bedding of the river Agra was excavated, filled with dirt to reduce seepage, and
levelled at 50 metres above riverbank. In the tomb area, wells were dug and filled
with stone and rubble to form the footings of the tomb. The advantage of well
foundations is that the cylindrical pits can be created top down, their fill can be
relatively stiff and they usually settle more or less regularly.
The period 1600 to 1800 AD
Amazing achievements where made in the past when so little was known
compared to what we do know to day. In Rotterdam, in 1620, the Lawrence Church
Tower was lower than the church tower of Delft. This was not acceptable and a two
stories wooden building was placed on top to make it 30 cm higher. It was cheap
5
The early construction of the bell tower of Pisa took place during 1173-1178. The
underground (a prehistoric embankment) made the foundation of masonry and mortar and
the four stories on top lean towards north (opposite to present). During 1272-1278 the
construction continued with elegant marble covering and with eight stories a height of 51
meters was achieved. The tower leaned south and settlements were estimated to reach 2
meter. During 1360-1370 the bell gallery was completed and the height reached 58 meter.
The weight amounted 145 MN and the obliqueness was then probably 2º (is at present
about 5º). During 1985-2001 a 14
th
Italian Pisa Tower conservation commission under
leadership of Jamiolkowski succeeded to relieve the inclination by carefully extracting
small amounts of soil underneath the uplifted side of the tower while the tower weight
caused the soil to be compressed again and straightened it for about 1º, sufficient to prevent
the sudden buckling collapse, which is thought otherwise to have been imminent.
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