A tale of two towers: Big Ben and Pisa - Royal Academy of ...
A tale of two towers: Big Ben and Pisa - Royal Academy of ...
A tale of two towers: Big Ben and Pisa - Royal Academy of ...
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A Tale <strong>of</strong> Two Towers:<br />
<strong>Big</strong> <strong>Ben</strong> <strong>and</strong> <strong>Pisa</strong><br />
1. INTRODUCTION<br />
A Tale <strong>of</strong> Two Towers<br />
This lecture tells the story <strong>of</strong> the movements <strong>of</strong> <strong>two</strong> world famous <strong>towers</strong> resulting from nearby<br />
construction activities <strong>and</strong> the application <strong>of</strong> novel geotechnical protective measures.<br />
The <strong>Big</strong> <strong>Ben</strong> Clock Tower was<br />
constructed in 1858, soon after the old<br />
Houses <strong>of</strong> Parliament were destroyed<br />
by fire. The clock tower consists <strong>of</strong><br />
load-bearing brickwork with stone<br />
cladding rising to a height <strong>of</strong> 61m; this<br />
supports a cast-iron framed spire, giving<br />
a total height <strong>of</strong> 92m. The tower is<br />
supported on a mass concrete raft 15m<br />
square <strong>and</strong> 3m thick which is founded<br />
within the Terrace Gravels <strong>of</strong> the River<br />
Thames, at a depth <strong>of</strong> about 7m below<br />
ground level. The tower is estimated to<br />
have a weight <strong>of</strong> 85MN, giving an<br />
average bearing pressure <strong>of</strong> about 400kPa. The clock face is<br />
55m above ground level <strong>and</strong> is out <strong>of</strong> plumb towards the northwest<br />
by 220mm. Thus the inclination is about 1/250 - an<br />
amount which is <strong>of</strong>ten quoted as being just discernable to the<br />
casual onlooker. This explains why tourists are <strong>of</strong>ten seen<br />
debating the verticality <strong>of</strong> the clock-tower!<br />
The Leaning Tower <strong>of</strong> <strong>Pisa</strong> st<strong>and</strong>s within the Piazza dei<br />
Miracole <strong>and</strong> is the bell tower <strong>of</strong> the magnificent Romanesque<br />
Cathedral. The tower is an architectural gem <strong>and</strong> would be<br />
one <strong>of</strong> the most important monuments <strong>of</strong> medieval Europe<br />
even if it were not leaning. The <strong>Pisa</strong> tower is very nearly 60m<br />
high, has a 20m diameter masonry foundation <strong>and</strong> weighs<br />
145MN. The foundation rests on a deep deposit <strong>of</strong> very s<strong>of</strong>t<br />
estuarine <strong>and</strong> marine sediments. The tower leans due south<br />
<strong>and</strong> in 1990 the seventh level, which forms the base <strong>of</strong> the bell<br />
chamber, overhung the ground by 4.5m. It is estimated that<br />
Aerial view <strong>of</strong> the <strong>Big</strong> <strong>Ben</strong> Clock Tower <strong>and</strong> the Palace <strong>of</strong> Westminster<br />
The Leaning Tower <strong>of</strong> <strong>Pisa</strong><br />
The <strong>Royal</strong> <strong>Academy</strong> <strong>of</strong> Engineering<br />
3
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