Though winter is only halfway done here in Australia, a report published this week in the Nature Scientific Review is enough to cheer cold hands and give hope to parents everywhere, while perhaps teaching a thing or two to engineers as well.
According to physicists, the secret to sand castle success is combining 99 per cent sand and one per cent water.
While some may question the importance of their contribution to science – physicists spending hours working in laboratories in Amsterdam and Paris constructing beach sand columns simply to come up with a complicated mathematical formula for a stable and long-lasting sand castle, especially when the answer is so simple-sounding – there is no questioning the science behind the find.
But according to the scientists the results are particularly significant and of interest for those in civil engineering and soil mechanics, where structural stability and integrity are paramount.
“If this optimum concentration (99% sand and 1% water) is used, sandcastles reaching five metres in height can be built,” said Daniel Bonn in the journal Nature Scientific Reports.
The key, according to the scientists, is to use just enough water to create ‘capillary bridges’ that will bond individual grains of sand. Too much water, they found, would weigh the sand castle down and make the structure prone to landslides.
The formula gets a little more complex when one considers the desired height-to-base-diameter ratio and sand compacting force. For example, a sand castle with a diameter of 7.5 centimentres could theoretically be built to a height of two metres.
While families are hardly going to start packing tape measures and measuring cups in their beach bags, there is a tip that everyone can take to the seaside, and that is the importance of packing down the sand. The researchers ‘thumped’ typical beach sand 70 times in a PVC pipe before the tube was removed to test the free-standing sandcastle.
In one final test, the researchers came up with the solution for everyone with an Atlantis fantasy – how to build an underwater sandcastle. The scientists found that using hydrophobic (water-resistant) sand, this was possible since the forces between grains in the structure were constant. Interestingly, because the water means the effective weight of the sand castle is smaller, it is possible to build more elaborate sandcastles under the water than above.
Family weekends at the beach may never be the same again.