How 'small' is it and what is the top-size of the fragments?

It is -5 mm particles average.

What is the size of the stockpile, moisture and top-size?

5mm is good as you're in with a chance of getting a decent sample - next key question many tonnes is the stockpile

Normally moisture it's about 6-8 %, but now it have been a changed and the stockpile grow bigger but I’ll give an estimation of the base dimensions of the pile considering that it is approx a cone volume 1675 m3.

The best solution is to move the total pile over a conveyor and take stop-belt increments from the conveyor - if you can hire a mobile conveyor and you have a loader handy that would be best option. Hopefully some of the coal people in the group can give you an idea of the size and number of

increments used in commercial coal sampling plants. Otherwise have a look at the Australian Standard for sampling AS 4264.1-2009 for some advice on the matter. You will still need access to a crusher and splitting device to sub sample the increments and again look at the AS standards for advice here.

If you can't get hold of a conveyor you could implement the fractional shovelling method using a small loader - but you will burn a fair bit of time doing this not to mention diesel. The idea here is to collect increments throughout the pile as you go, and crush and split the increments as you go. You can cobble together a reasonable rotary splitter out of a carousel of 6 44-gallon drums and a hopper to break down 1 m bucket increment into something manageable for crushing and splitting by

hand. Aim to do at least 30 to 50 of these through the pile.

Certainly a challenge but at least the top-size is manageable - if this is for a commercial transaction you may wish to get some professional advice.

Sample the stockpile manually is cumbersome. Automated suggestions are expensive. A form is quartering the stockpile; I suggest separating it into two lots the stockpile by increments, an increase to a lot and 4 increases to another lot. After re-subdivide Lot 1 increment generated to obtain the sample. But it is still cumbersome, I cannot think otherwise.

Ok thank you for the advise learn one thing and hope I don't repeat the same mistake:

It is better to sample the coal before it goes to the pile;
I've learned about the stop-belt sampling method few months ago it seems to be interesting i would try to do whenever i have the possibility, but I don’t think my superiors will accept but ok thank you for everything.

Would sonic drilling be an option? I know the recoveries in unconsolidated materials are very good and the samples can be taken without introducing any fluids to the stockpile.

The solution we have a client who did cooking coal in Germany with great success. Obviously the handling of sample and barrel is a bit challenging but can be won.