Article - Issue 27, June 2006
A Question of Scale
Dr Scott Steedman FREng FICE
Dr Scott Steedman FREng
Integrating new nano-scale elements into our existing systems,and safely and efficiently delivering the value that engineering brings to society will be amajor challenge for all of us.
1 June marked the start of the 2006 hurricane season in the Gulf of Mexico, and work continues on the levees and flood walls in New Orleans to restore levels of protection at least equal to pre-Katrina conditions. The facts that have emerged from the Federal Task Force investigation (known as IPET) this month reveal that large parts of the hurricane protection system were actually built to a lower height above sea level than intended. There were around fifty breaches across the five parishes where the defences were overwhelmed by scour, erosion or foundation failure. A foot of rainfall, floodgates that were not closed and backflow through the pumps contributed to the catastrophic flooding.
New Orleans pre-Katrina was a city with a population of around 500,000. Ten months on and the population is only half that number. Large areas are effectively abandoned. One likely scenario being examined is that it will remain this way for the foreseeable future: figures from March 2006 show that only 7 out of 22 hospitals have reopened, school enrolment is less than 10,000 (pre-Katrina it was 65,000) and the city retains a deserted feel. Construction is booming but restaurants close early through lack of staff.
The challenge of creating a functioning system composed of a multitude of elements is a perennial task in engineering. On the one hand a city is to be defended, and on the other those defences depend on elements that have to work together, on demand, no matter how minute that element may be. The city of New Orleans is protected by hundreds of miles of levees and floodwalls. The geological features that lie immediately beneath the canals and flood defences range from thousands of metres to a few metres or less in typical dimension. The foundation failures that led to four of the breaches in the centre of the city were governed by mechanical processes between sand and clay particles that were millimetres or tens of microns in size.
As a student I was fascinated by the scale of engineering. Not just the scale of the finished products, be it a city, an offshore oil platform or a microchip, but the idea that engineering had to accommodate the interaction between materials that themselves spanned a vast range of dimensions. If we were working with an artist’s palette, then our engineering canvas has traditionally exploited the properties of everything from the finest pencil line to the largest monolith. If the clay particles beneath the New Orleans levees were the size of dinner plates,a piece of gravel would be the size of a high rise building.
On the flight back from Mississippi, I recognised an engineer from the research centre of the Corps of Engineers, who was travelling to Brussels to attend a conference on Carbon Nanotubes, searching for new materials that in the future might support a whole new era of engineering. We have heard of applications of nanotechnology in electronics and ICT, but the idea that we could soon see new materials 10 or even 100 times stronger than the highest strength materials we know today is a remarkable thought in other sectors.
As with the first introduction of steel or carbon fibre,we would be looking at a new generation of materials and a new wave of opportunity for innovation in engineering design and production. Ultra high strength materials would release potential for new sorts of structures, engines or the ability to greatly increase the life of objects by reducing wear.
Nano-bots might replace robots in the popular imagination, capable of working in the tiniest of voids to investigate performance, repair damage or build new structures. In geotechnics, there is already talk of ‘pore space engineering’; the idea that we could alter the properties of the ground through working inside the microscopic voids between soil particles using chemical or biological processes.
Of course, adding nanomaterials and nano-bots to our palette would increase yet again the range of mechanics that engineers need to understand and exploit as we bring such materials into everyday use. Integrating new nano-scale elements into our existing systems, and safely and efficiently delivering the value that engineering brings to society will be a major challenge for all of us. Too late for New Orleans, perhaps, but some day soon?
Dr Scott Steedman FREng