The most serious danger from blown sand is train derailment, so trains usually run at reduced speed on windy days as a precaution. âFewer trains pass per hour,â said Dr Lorenzo Raffaele, wind engineer at the von Karman Institute for Fluid Dynamics in Sint-Genesius-Rode, Belgium. “This results in a loss of capacity for the railway, which means a loss of money.”
Several techniques can be used to protect infrastructure from blown sand. Structures such as barriers or ditches can be installed to trap sand. On railways, it can be useful to raise the rails, where the space below can accelerate the wind and clean up the sand. However, the measures are generally not as effective as they could be. This is in part because they are still largely designed by trial and error, where a solution is chosen based on intuition and tested in the field after the railroad is built, which is expensive and can take a lot of time. time.
âA more rigorous approach is needed in order to avoid problems (such as construction delays),â said Dr Luca Bruno, associate professor of structural engineering at Politecnico di Torino in Italy.
While there are currently ways to assess the performance of sand mitigation measures, they often do not meet the needs of infrastructure designers. Existing computer simulations, for example, typically only model wind flow models without incorporating the behavior of the sand itself, and more advanced models are still in their infancy. They can therefore only give a rough estimate of the effectiveness of a measure.
Wind tunnel tests can also be performed to reproduce the behavior of sand blown by the wind. However, only a few facilities in the world allow experiments with sand as it spreads everywhere and can damage equipment. In addition, the grains of sand would have to be reduced in size in the experiments since the proposed measurement models are reduced, which is not possible because it would become dust, which would behave completely differently. It is therefore difficult to extrapolate from the results to determine how they would work at full scale. âThis is a big limitation of wind tunnel testing,â said Dr Raffaele.
Dr Bruno and his colleagues therefore aim to propose new techniques to assess the risks associated with sand, while devising new sand mitigation measures and new ways of assessing their performance, within the framework of the SMaRT project. They focus on alleviating problems caused by sand near railroad tracks. âAt first we were spurred on by a practical need expressed by industry,â said Dr Bruno.
Team members have developed a computer simulation that can help assess the performance of a sand mitigation measure before railway construction. Their simulation takes into account both air flow and sand movement, and takes into account different phenomena such as erosion, sedimentation and sand avalanches, simulating their effect around the complicated shape of a track.
âWe are able to predict how wind, sand and railroads behave under real conditions,â said Dr Bruno.
âWe are able to predict how the wind, the sand and the railroad will behave in real conditions. “
Dr Luca Bruno, Politecnico di Torino, Italy
Their computer simulation is now being used to develop a hybrid approach to assess the performance of sand mitigation measures in another project called HyPer SMM. Dr Raffaele and his team improve the model by incorporating wind tunnel test measurements with sand.
âThis allows us to compare wind tunnel measurements and numerical results, identify deviations and fit the computer model to the wind tunnel measurements by adjusting the value of certain parameters,â said Dr Raffaele.
So far, the team has performed initial wind tunnel tests to characterize how sand moves at different wind speeds, starting with a flat sand bed. They measured the concentration of sand in the air and the speed of individual grains of sand, for example. Their results were used to fit the computer model.
Next, they plan to conduct wind tunnel experiments with sand and scaled-down sand mitigation measures, focusing on barrier or ditch solutions, as these are the most widely used. The measurements taken in the wind tunnel during the introduction of a mitigation measure will be compared with those obtained from the simulation for the same measurement at reduced scale. Once both methods give the same results, the model can be validated. It can then be applied to test the mitigation measure on a large scale, bypassing the problem by extending the wind tunnel results.
Dr Raffaele and his colleagues plan to make all of their results publicly available. Companies and universities will be able to validate their own computer simulations using, for example, their measurements in a wind tunnel. Or the results of a validated computer model could be used to help predict the effectiveness of a sand mitigation measure before infrastructure construction, using information about local environmental conditions, such as speed and the direction of the wind and the size of the sand grains.
Dr Raffaele expects their hybrid approach to be used primarily by companies building new rail lines or expanding existing networks in the Middle East, North Africa and China. But it could also be of interest in coastal areas of Europe, where windstorms often cause sand to accumulate around buildings and infrastructure in small villages. A tram line in northern Belgium, for example, is often disturbed by sand on the tracks, as in a storm last September. âThey had to clean everything for several days,â said Dr Raffaele.
In addition to new approaches to assess sand mitigation measures, more effective measures are also needed. The SMaRT project team developed a new type of barrier with a curved projection at the top, designed to be placed between a sandy area and a railway track. It changes the flow of the wind and reduces the speed of the wind so that the grains of sand fall. The sand is therefore trapped far from a railroad track, which would reduce costs since rail traffic would not need to be stopped to clear the sand.
“Workers would sometimes need to remove the sedimented sand around the barrier, but this maintenance is easier (since it is) away from the railroad tracks,” said Dr Bruno.
They also designed a second sand mitigation measure, which is in the process of being patented. It is intended to be placed near a railroad track and is designed to harness the energy of the wind to disperse the grains of sand. Dr Bruno says that ideally the two measures would be used together. The barrier would stop most of the sand while the second measure would disperse the remaining grains.
The team also examined how advanced technology can improve the site assessment of mitigation measures. In field trials in the Namibian desert, they used some of these techniques to assess the performance of a special track system that had been installed to help alleviate sand on a railroad track. Typically, assessments are done using anemometers to measure wind speed and a device called a sand trap to assess the amount of sand carried by the wind. However, in this case, they used a laser scanner to measure the sedimented sand and piezoelectric sensors to measure the flow of sand. “These measurements are much more precise than the sand traps adopted so far,” said Dr Bruno.
Using this new technology, the team was able to develop a new method that can be adapted to assess the performance of any type of sand mitigation measure in the field. While their computer model will now help evaluate measurements at the initial design stage, field testing will remain important at the end. “They are meant to check that everything is fine before a railway line is in service,” Dr Bruno said.‘Measurement tools and techniques must therefore be precise, reliable and robust. ‘
The research in this article was funded by the EU. If you liked this article, consider sharing it on social media.