Bedding sleepers in ground to support site office/shipping container.

Hello,
I am going to be using a site office as added space to my existing workshop. It is 20ft X 8ft and I've been told weighs about 2 tons. As you will know all of the weight it put on the four corner feet and nowhere else to stop rusting or water ingress.
I have some old sleepers ( 6 inches thick) cut in half lengthwise ( to about 4ft) and I have dug 4 trenches to about 12 inches deep. One sleeper will support each corner. I plan to fill with mortar as a bed to 8 inches and have the sleepers sticking above ground level by a couple of inches and all level to each other.
My question is should I use a wet mortar bed, a slightly wet dry mortar bed or can I just bed the sleepers on well compacted sharp sand ? As said each corner would presumably have to take 500 kg weight and the site office would not have much more weight inside it.
Thanks
James Ps the soil is a dryish clay type.

Having the sleepers trenched will just let them rot more quickly.
Fill the trenches with hardcore, put the sleepers on top, stop fretting.
Or fill the trenches with concrete & just use the metal feet.

Thanks for advice. I will probably just go for the fill with concrete option. Do you think 12" deep will be enough. How long would concrete need to set sufficiently ?

Once concrete is set it continues to harden over many, many years I believe.
If I was putting half a ton on it I think I would wait at least 2 weeks but someone else may say longer or shorter.

Think the usual rule of thumb with concrete is a day per inch. 12 inches (300mm) isn't deep enough to be below the frost line or be protected from ground heave but on a temporary building who cares, it'll be fine, if it moves get a jack and relevel it.

Why not just lay 4 sleepers on the ground and put the container on top?
Point loading the sleepers seems odd and may sink.

Thanks for advice all. I want the container to be as close to ground level as possible and raising up onto sleepers would make too high.

woodman-46 said:

Thanks for advice all. I want the container to be as close to ground level as possible and raising up onto sleepers would make too high.

Click to expand...

You could just plonk it on the ground, if it's lifted on slings you'll need a way for the driver to get them out from underneath the cabin