Soil classification and implication

wander25m · Jun 28, 2006 4:29 pm

My soil tests come back with a M/H rating, plus a P for presence of uncontrolled fill. The developer said there were only cuts and no fills when the land were developed. The P class would require compaction etc otherwise special footing design is required. My question to any builder out there is:

-normally there is an "allowance of fall" typically 0.5m or 1m across the site. does that mean the top 0.5 or 1m will be removed, compacted to achieve compaction level for building? If not, what does that mean ?

-the builder can't just lay the bloody slab on the ground as it is can they ? there definitely has to be some compaction, leveling required, does that change the "uncontrolled fill" thingy?

thank heaps
Newbie

builda · Jul 01, 2006 12:27 am

Quote:

My soil tests come back with a M/H rating, plus a P for presence of uncontrolled fill. The developer said there were only cuts and no fills when the land were developed.

No matter what anyone 'said' was there a soil test done? Also, the fill could be old as in an old sink hole or dam filled in even before the development - not uncommon!

Quote:

The P class would require compaction etc otherwise special footing design is required. My question to any builder out there is:

-normally there is an "allowance of fall" typically 0.5m or 1m across the site. does that mean the top 0.5 or 1m will be removed, compacted to achieve compaction level for building? If not, what does that mean ?

No, not necessarily. Vegetation is to be removed but not down that deep unless there was a cut and fill design for the block. Certainly not standard. Natural soil does not need compaction for a house slab but issues with fill could require it.

Quote:

-the builder can't just lay the bloody slab on the ground as it is can they ?

Yes, so long as the vegetation is gone but the whole slab design should be completed by an engineer with his design based on a site specific soil test. That is the only way that you wil know it is right. The best failsafe way is to get this done BEFORE you sign the building contract as it will avoid a nasty variation.

Quote:

there definitely has to be some compaction, leveling required,

No, raft slabs are designed to be like a raft where the only structural contact is via the edge and internal concrete beams. The area between the beams does not require much support at all but as stated earlier does require the vegetaiton to be removed.

Quote:

does that change the "uncontrolled fill" thingy?

Uncontrolled fill is a problem if you want to build on it. Maybe get your builder to cost the option of screw piles - much cheaper than trying to dig out the fill and recompact. The screw piles simply drill down through the rubbish and found on solid ground underneath. Again, you need an accurante soil test to determine how deep the fill is as screw piles may not even be appropriate.

Hope that helps a little bit?

wander25m · Jul 01, 2006 10:15 pm

Great thanks for your response builda, No I haven't signed any building contract, so I am just tinkling between the ideas of getting it done myself, or squeeze a litte more from my developer as I can literally reject the land with a P class soil.

However we've resolved the situation amicably so I'm quite happy and looking forward to my home being built soon.

Thanks.