News letter Dam edition

Ingeokring Newsletter
Professor’s Column: Ode to ground
Prof.dr.ir. Frans B.J. Barends, GeoDelft/TUDelft
When speaking about water in the Netherlands, everyone is
informed: the eternal battle against the sea, controlling
large rivers under intensifying rain showers, sea level rise, as
well as the importance of water for drinking quality, transport
and recreation.
When speaking about air, there are similar appealing subjects:
sailing and surfing, Schiphol airport, daily weather
forecasts, fine dust and wind energy.
However, when speaking about ground the topics are less
vivid: landscape, agriculture and spatial planning. Water we
drink, air we breath, and from soil you become dirty. The
unrealised fact is that almost all our comfort is based upon
ground that we possess: water and air come from elsewhere.
With ground, we control the sea and rivers by making dams,
dikes and dunes. With massive earthen dams we control
nature, influence the hydrological cycle and create energy.
On ground we have built impressive infrastructures: cities,
roads, railways, tunnels, bridges, pipelines, and we keep on
doing so at an increasing scale. We are experts in engineering
with ground. Let’s expand on the significance of ground
for our existence, with focus on the Netherlands.
Ground is protection. For at least ten centuries, the Dutch
have built dikes and polders to withstand surging seas and
rivers. Originally, by hand, all groups of society contributed
as shown by names like Thief’s-dike and Children’s-dike,
later by wind energy produced by thousands of windmills
and thereafter steam and electricity took over, coping with
an ever-increasing scale of lowland development. The social
organisation by water boards, at a level of municipal authority,
is unique in the world and paved the way towards an
excellent management system for optimum safeguarding
against flooding. However, reclaimed lands (particularly
marshlands) shrink and compact. As a result, ground is subsiding.
Along the coast at a maximum rate of 10 cm per century,
in polders at an average rate of 25 cm per century, and
in some peaty areas even at 150 cm per century, and more. It
invokes a permanent concern, but at this rate the safeguarding
against floods is technically manageable, even with the
expected sea level rise . Since 1996 all protection works are
controlled by law each five years and in general the result is
that about 50% is sufficient, 30% is uncertain (lack of data)
and 20% must be improved. The government spends about
1 billion euro annually to maintain sufficient quality of protection.
The public, now being informed in exact numbers
about the status quo, complains about the lack of safety.
Only 50% is guaranteed. But at present they are safer than in
the past. Improvements take years and we should not forget
that a life without risk is unrealistic. Our ancestors knew
better and survived.
Ground is support. Amsterdam is founded on hundreds of
thousands of piles, tourists are told. Indeed, all Western
Netherlands’ structures are supported in smart ways, exhausting
the available bearing capacity of the ground which
is only better at the level of glacial sand layers at depths of
more than 10 metres. The early foundations of monumental
buildings consist of thin wooden friction piles of 6 metres
length at most, sometimes bundled in hoods (“huien”). During
the 17th century, pile-driving machines (by hand) allowed
to install longer wooden piles reaching solid sand
layers. At present, a great variety of foundation methods are
applied reaching depths of 50 metres and more. Now, the
challenge is to build in complex situations with minimum
hindrance to the adjacent environment. The construction of
the north-south metro line in Amsterdam is a perfect example.
Also in the past smart solutions were applied. Around
1650 a strong southwestern storm blew the bell tower of the
Laurens Church in Rotterdam lean, against the nave. The
tower founded on short friction piles had become top-heavy
by the last build-up in fine Italian marble. Lead by the city’s
engineer, a new foundation of long timber piles was driven
around the basement and the heavy tower was adjusted
and put on the new foundation using iron chains and horsepower
without a scratch, an incredible achievement. How
exactly is not described. If we look at Rotterdam, to the new
city centre with tallest buildings, the Kop van Zuid, the Van
Brienenoord- and Erasmus Bridge, the enormous harbour
and the many tunnels, recalling the local very soft soil conditions
and high groundwater levels one may see impressive
demonstrations of sophisticated engineering, however invisible.
Ground is mobility. In the West of the Netherlands road
and railway infrastructure is built on sand embankments.
Without such support, no straight track is possible. Building
roads on weak grounds that hardly settle is not an easy matter,
mainly due to the heterogeneity in the underground.
Ground is not transparent. Modern technologies like acoustic,
seismic and radar reconnaissance are limited. Mobility
needs a firm basis; with proper roads we can move around.
The underground transportation infrastructure is impressive.
Dam edition | Double Issue 2007/2008 | 16