structural
challenge
daM design
structures, as the rock medium allows some water spillway capacity to accommodate larger floods,” he
seepage. However, because of the enormous quantity of says. such changes could require dams to be raised and
materials required to build a dam, the design and the spillways to be reinforced as design criteria adapt to
type of fill is often dictated by what materials are available allow for the increasing severity of storm events.
locally, rather than by performance criteria alone. One dam that could have benefited from such
“The approach has changed a lot over the years,” retrospective attention is the Ulley reservoir near
says Hinks. “There’s now much greater awareness of the Rotherham, UK, which suffered from erosion of the
dangers of seismic liquefaction in dams and foundations, downstream face in June 2007 after storms. The
and consequently the avoidance of low density sands. turbulent action of the water over steps that were built
Hydraulic fill has fallen out of favour.” in 1873 led to some stones being moved and
seismic liquefaction occurs when the fill material in undermined the dam itself.
at 7.8 on the richter scale, the earthquake that hit the dam loses strength and stiffness under earthquake The age of assets is a problem, particularly in the
China’s sichuan province caused catastrophic damage to loading. it happens in water-logged (saturated) soils as UK, where the average dam is 110 years old. This,
infrastructure and resulted in more than 69,000 fatalities. forces from the movement generated by the combined with new legislative requirements to produce
For days, residents of the town of dujiangyan waited earthquake cause spaces between the grains of soil or flood hazard maps along with risk management plans
for a second catastrophe to strike, as damage to the sand to collapse, leading to the fill no longer being able (eU Floods directive 2007), and requirements to
156m concrete-faced, rockfill Zipingpu dam triggered to sustain the pressure from overlying soil or structures. quantify individual dam risk and establish contingency
fears that it was on the verge of more extensive failure. This fill material then flows like a liquid and can cause measures (Civil Contingencies act 2004), is leading to
“Few large dams have been exposed to such severe extensive damage. new responsibilities for engineers.
shaking and people will pore over the performance of Hinks also sits on the seismic committee of the “The biggest challenge for the profession is 43
the dam for some time to come,” says chairman of the international Committee of Large dams (iCOLd), a not technical – we can solve those issues – it is about
British dam society Jonathan Hinks. forum of 88 countries that work together to improve knowledge transfer and succession planning,”
technical guidance and experience in dam engineering. says Hughes. The lack of major new dam construction
Read the signs “We will next meet in Bulgaria in June. in the UK is considered to be one reason that few
“every incident is learned from and there are already improvements in practice often follow a close study of young engineers are specialising in dams and hydraulic
some early findings,” says Professor andy Hughes, incidents and failures, both worldwide and in the UK, engineering. in China and india, where a wealth of
atkins’ director of dam engineering. “The reservoir was where post-incident reporting is likely to be made major dams, mainly for hydroelectric power generation,
only a third full, but there was cracking and obvious mandatory,” he says. are under way, there is no such problem. But such
leakage,” he says. This goal is supported by Professor Hughes, who is schemes are also contentious, with the anti-dam lobby
The dam holds 1.1 billion cubic metres of water, but working with the environment agency on arguing that they should not go ahead.
was only holding 320 million cubic metres at the time of recommendations for improving reservoir safety. such “There is also a requirement for engineers to be
impact, greatly reducing the dynamic loading on the mandatory information, he says, would be an extremely much broader in their knowledge and views and not
structure. But, despite this, the shallow depth and valuable resource for all designers. This research is hide behind the technical design. You have to be an
severity of the quake caused damage serious enough to about to be submitted to the department for the environmentalist, an accountant and a politician,” says
raise concerns that the structure could fail and unleash environment Food and Rural affairs and identifies 49 Hughes. To this end, he is assisting the University of
torrents of water, further devastating areas downstream. areas that require further study. Bristol in teaching undergraduate courses in dam
such concrete-faced rockfill dams are designed as a engineering and supporting research initiatives. “We are
concrete slab, or series of concrete slabs, that sit on a New challenges promoting dams in a world where there is a desperate
rubble transition zone above the mass of rock at the heart One area highlighted is that of climate change and its need for water, power, food and irrigation,” he adds.
of the dam. This creates a water-tight membrane. They effects on dam safety. “issues include more frequent, “engineers must talk the same language as
are generally expected to perform well in earthquakes extreme floods, resulting in more frequent overtopping environmentalists. Better training through a good centre
and considered to have less risk of failure than earth-filled of dams and perhaps the requirement for increased for learning seems a good place to start.”
daMs COULd Be Raised and sPiLLWaYs ReinFORCed as design CRiTeRia
adaPT TO aLLOW FOR THe inCReasing seveRiTY OF sTORM evenTs
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52