Building the tallest sandcastle

The Canadian National Exhibition (CNE) opens in Toronto next Friday (can’t wait!) and they hold an international sand sculpting competition every year. I’m always impressed by the size and detail of these sculptures and wonder if the competitors ever consider the science that’s behind their work?

Recently, I came across an interesting piece of research on‘s Scientific Report on How to construct the perfect sandcastle. Maryam Pakpour of the Institute for Advanced Studies in Basic Sciences in Iran, and colleagues from the University of Amsterdam in the Netherlands and the Laboratorire de Physique Statistique de l’ENS in France investigated the answer to this question by determining the relationship between height and stability of a sandcastle.

Just by scooping up a handful of dry beach sand, you know that you can’t build a sandcastle with it. Dry sand simply won’t hold any kind of shape as it can hardly support its own weight. You can transform these loose grains of sand into an “adhesive”, formable material by adding water. Wet sand holds because water forms liquid bridges between sand grains. But add too much water and you’re left with an unstable pile of sand that ultimately collapses (think landslides).

Aside from water content, the stability of sandcastles is equally dependent on having a sturdy base. Just look at the world’s tallest sandcastle which stands at 11.53 m high. Built by Ed Jarrett of the United States, his sandcastle has a fairly large base and progressively narrows towards the top.

World’s tallest sandcastle (Source:

In this research, the team started by investigating the stability of columns of wet sand, which would allow them to determine the maximum height of sandcastles that could be built. The idea is that a column of sand reaches its maximum high when it starts to buckle under its own weight.

The team reported a mathematical model that considered the maximum strength of sand packing, density, and gravity, and also verified their model experimentally. They found that the maximum height (h) varies with the radius of the column (R) as hmax ~ R2/3. Beside the size of the sandcastle base, the model shows the height of the sandcastle could be increased by increasing the compaction of sand (a known technique to sandcastle builders). Furthermore, decreasing the density of the sandcastle would also allow a taller sandcastle to be built. The team tested this idea by building their sandcastle underwater, decreasing the effective density of the sandcastle.

A sandcastle built underwater

The team notes that normal beach sand can’t be used to build underwater sandcastles because the liquid bridges holding the sand grains together get destroyed. But they show it’s possible to build an underwater sandcastle using commercially available hydrophobic (water-hating) sand because air rather than water forms the bridges between sand grains.

The tallest “sandcastle” the team built was a uniform cylinder that stands at 1 m tall, so it is unlikely that competitive sandcastle builders will follow the team’s “recipe” on building the perfect sandcastle–especially when it comes to building sandcastles with complex shapes and designs. However the study offers an improved understanding of the behaviour of partially saturated granular materials, and may be useful to those working with geophysical applications such as soil stability.

Pakpour M, Habibi M, Møller P, & Bonn D (2012). How to construct the perfect sandcastle. Scientific reports, 2 PMID: 22870378

Featured image by Flickr’s marc e marc

39 responses to “Building the tallest sandcastle

  1. Pingback: Blogs Worth Cheering For: So Close, So Far Away | Science Cheerleader·

  2. I’m taking my kids to Lake Tahoe this weekend…and I’ve decided to show them the pictures in this post, just to make them feel truly inadequate as they construct their silly little sand castles. 😉


  3. An underwater sandcastle? I had no idea that was even possible. The sand would probably need to be the insistence of clay.

    The St. Regis in Monarch Beach has an elaborate sandcastle built in their lobby every year at Christmas time. The builders really are incredibly talented artists.

  4. Pingback: Building the tallest sandcastle | AuzBul·

  5. I remember going to the Ex as a kid! I haven’t been in decades, but at that time, I had several cousins & aunts & uncles in Toronto, and we went to the Ex every year. I still have tiny Coke bottles that were given out with each cup you bought.

    The sandcastle photo is brilliant. Makes me want to go to the beach and put theory into practice. Thanks for the inspiration!

  6. cool! i was born and raised in toronto (i live in montreal now) and for the life of me i can’t remember there being sandcastle competitions at the ex!!! i used to go every year! i was actually just there last weekend and didn’t see anything of the sort (though i did see some butter sculptures)! such a great post, thank you!! x

  7. This is really fascinating – I had no idea. And the world’s largest sandcastle is amazing! Looking forward to checking out the rest of your site. And, of course, congratulations on being fresh pressed!

  8. Pingback: Redgrove Wet Sand Beach « myothervoices·

  9. Pingback: Blogs Worth Cheering For: So Close, So Far Away | Science Cheerleader·

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