Sea sand...?

Question

Ok...if you at the beach and you dig a hole..how far can it go? Like how deep untill you can't dig anymore..thought it would be interesting to know..thanx!

Answer 1

You can dig a little below the level of the sea water; but not far.. This is because the sand below the water level is saturated, and the water takes up all the space between the sand grains, and the sand grains pack as closely together as possible. Ever noticed that the sand above the water level is softer ( less dense) than the wet sand; and the dry sand above is even lighter? That is because the pore spaces are taken up by air, which of course is a lot lighter than water, and the air does not help to pack the sand grains as close together.

The natural 'angle of repose' for dry sand is about 30 degrees (slope 1 in 2), That is why, if you dig a hole in dry sand, the sand keeps running in, to fill the hole. If the sand is damp (containing about 5% moisture), the moisture helps to bind the sand together, and you can dig a deeper hole with vertical sides, and construct sand castles using damp sand.

Below the watrer level however, where the sand is saturated, the angle of repose is only about 1 in 5, and you can only dig a very shallow-sided hole (say you dug down 1 metre, the hole would then have to be 10 metres across - one metre in five, for each side of the hole),

Technically, you could dig a quite deep hole in the sand, but it would have shallow sides. When commercial sand dredging operations extract sand from below water level, they have to take these low 'stable dredge slopes' into account., and a dredge hole ten metres deep could be more than 100 metres across.

I used to run a sand dredging operation.

Answer 2

How long is a piece of string?

It depends on the beach. Some 'beaches' are bedrock or a thin layer of sand, some are much deeper.

However, it's pretty safe to say you can't dig much past sea-level if you're using your hands or a bucket and spade. Then the hole will fill with water and it'll be a mess...