Can foundation trench be skipped in specific conditions?

Hi good people.

I live in an area with "a subtropical climate with abundant sunshine" - it never frosts, and never snows.

The ground onto which I am thinking about placing earthbags is also very very hard. It's the type of ground that one never wants to dig into!

The specific site I have in mind for a small earth-bag project will be completely protected from moisture and water. Like this:



Also, the earth-bag component of this project (should it go ahead) will only be about one metre high max, possibly only half a metre. Straw bales might constitute the walls thereafter, or even timber framing and cladding.

Considering the specific conditions I have listed, do I need to make a rubble-gravel trench, or can I get away without it?  

Thanks,
Dave  

I guess I would be concerned with ground water.
A roof can make a big difference but water will wick through most soils.

William Bronson wrote:I guess I would be concerned with ground water.
A roof can make a big difference but water will wick through most soils.

I'm certain that no ground water will get near the bags.

Then the main issue will be whether the existing ground surface is firm enough to hold the weight of the total future construction without sagging. One purpose of a footing is to spread the wall load over a large enough area that it doesn't sink in. If the surface is packed hard, you may be able to build directly on it. If you can dent the surface, you may need to dig down to more solid ground.

I'd still do the trench. I love that you're certain that no ground water will get near the bags. That's great. I'm certain that, despite your certainty, there's a large probability that water will be drawn up through the soil in a way that is completely impossible through a gravel trench, to dampen your supporting wall bags from the inside-out.

Digging a foundation trench might be difficult. Trying to fix the problems caused by not digging a foundation trench would likely prove completely unworkable.

Could a foundation trench be skipped entirely in certain conditions? Probably. But those would be where you have another, probably more intensive, method of keeping water from getting at your structure. The foundation trench is really the simplest, safest approach.

-CK

I would not skip it.  The depth and width of it may be debatable.

david pittaway wrote:Hi good people.

I live in an area with "a subtropical climate with abundant sunshine" - it never frosts, and never snows.

The ground onto which I am thinking about placing earthbags is also very very hard. It's the type of ground that one never wants to dig into!

The specific site I have in mind for a small earth-bag project will be completely protected from moisture and water. Like this:



Also, the earth-bag component of this project (should it go ahead) will only be about one metre high max, possibly only half a metre. Straw bales might constitute the walls thereafter, or even timber framing and cladding.

Considering the specific conditions I have listed, do I need to make a rubble-gravel trench, or can I get away without it?  

Thanks,
Dave  

I think that you would be ok skipping it, if is as dry as you said. How is your average humidity? Subtropical? Does it rain? Subtropical arid?

Wicking of ground water would still occur with a concrete beam, unless you fit a plastic or steel sheet barrier.
I have seen slabs of rock set on the ground, in Melbourne where 4 storey brick buildings have been built.
The top soil is removed and the rock is laid on hard clay.

In your case I would try it without concrete, you stated it's a small project and nothing beats experiments.
Perhaps clean loose soil away, lay down a moisture barrier and see how it goes.