Where I First Heard the Term “Blowing Sands”
This page is written by Will. I am am Geologist (amongst other things) and I also worked on Land Based Drilling Rigs for about a year in my 20’s. Some of the rigs I worked on were shell and auger rigs, and it was working with this sort of equipment that I first heard the term “blowing sands”.
What do Blowing Sands Look Like
Blowing sands do not look overly different to any other sand although if you were to pick up some in your hand there would they would be wet. In order to blow sands need to be in a mixture with water or other fluid (should also bear in mind that is entirely possible for Sands to blow as a result of gases although this is much more rare) but in short they look similar to the wet sand which you might scoop up along the shoreline at a beach.
How do Blowing Sands Behave
In order to understand why blowing sands are named as such we must first have a little bit of an understanding of how a shell auger drilling rig works.
When drilling through sand it is typical to drill or bore an initial hole. After a while the sides of the hole will start to collapse, and it is then that you hammer in some casing. This casing is a steel tube which is a slightly larger diameter than the cutting tool that you might be using.
As you drill (or bore) the hole deeper and deeper and hammer further casing down further and further you will eventually reach the water table and this is where you are most likely to encounter blowing sands.
Sands mixed with water when exposed to vibrations will very often behave as a liquid, the sand water mixture combined with the vibration of the cutting tool will become liquid and it will “blow” back up inside the casing. One minute you’re at 10 meters depth and the next minute you’ll hole is only 6 meters deep, because the sand and water mix is flowed up (blown) inside the casing and then set solid again so this is why drillers call blowing sands as such: because they blow back up inside the casing when given a certain set of conditions.
The liquefaction process is caused by water or air being forced in between the grains of the sand (from vibrations or pumped water) and reducing the friction between them, to the point where it can flow.
Search Terms
When the vibration is added and the solid becomes a liquid this in geological terms is a process known as liquefaction it can happen on a very large scale during an earthquake when buildings or other heavy loads, that our built on sandy soils. The wet soils and the shaking of the ground can cause the sands to liquefact and the buildings literally starts sinking to the ground so it’s quite an interesting topic . It can also cause less dense items in float, as shown in the below video.
In the context of geo hazards you will also see the term running sands. “Some rocks can contain loosely packed, sandy layers that can become fluidised by water flowing through them. Such sands can ‘run’, removing support from overlying buildings and causing potential damage.”.
So if you were advancing a borehole through either of the above “soils”, it would quite likely “blow”. Drillers find this very annoying as it can undo a couple of hours work, and many drillers get paid for the depth of the hole they are drilling, you might find that they add on additional words at the beginning of the phrase such as “f***ing blowing sands” etc etc.
