Buliding a house on a fill yet has to be made

[mar2805]

Hello.
We are in progress of designing 4 modern houses on a location that mainly rocky soil.
The client wants the hoses to be elevated for 3m above the egsisting level due to the sea view.
I have never designed anything on a fill that yet needs to be constructed.
Can you give me some gudiance on how the fill should be made, what materials to use, what compaction degree, and finaly how to test the fill and get the soil/material parameters like angle of internal friction, densisty of soil.....
Thank you

 

[phamENG]

If you don't know, you should a hire a geotech to design the fill. Even if I knew, I would still insist a geotech design the fill. Engineering of dirt is sort of the point of their existence.

 

[dik]

as pham notes, you need a geotekkie...

Is the object to build an elevated house with the intent of providing fill under it as sea level rises? An alternative is to build an elevated struct with adjustable 'stairs' or to provide access. The fill required at the time of construction. This is where the geotech info is needed. You need to provide a type of fill that provides support when it is saturated and a stabilised slope or containment for it. The containment has to be designed for the saturated/unsaturated lateral soil pressure as well as the weight of the structure. It's an interesting task...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[mar2805]

Thank you for the advices.
One fast question, is there any correlation between the dynamic plate load test and the Proctor test?

 

[EireChch]

none at all. plate load test is a load-settlement type test and can be correlated to a CBR.

Proctor testing determines the optimum dry density

 

[mar2805]

Not the "standard" plate load test, but the dynamic plate load test...I think there is a big difference.
Can you comment

 

[EireChch]

Sorry, you are correct. The dynamic load test is a light weight deflectometer test. I have heard of them but never seen them used or specified.

Seems like there is a german DIN standard for correlation to degree of compaction.

I cant say more than that, but if it is a german standard then it is certainly a good reference.

 

[LittleInch]

Are the house foundations intended to sit on this mysterious yet to be defined fill or would you need to included piles or similar down to the rocky soil?

Anything which has fill will always settle after a period of time - the issue is just how much and how long do you leave it.

A good soaking from the air (rain) always does it some good, so min 4 months?

Can't you just build a large concrete frame and use the space for a garage or something?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BigH]

First off - we do not know what the fill will be sitting on. If it is soft or firm clay, 3 m of fill will cause settlement by consolidation. This needs to be addressed. Consolidation can take a long time. Do we need to speed up the consolidation by drains, etc.? If it is on stiff clay - there might not be a problem. Similarly, what if the supporting soil to the fill is cohesionless?

Secondly - you have not given us any idea of the topography of the land onto which the fill will be placed.

Thirdly - the use of engineered fill. Best choice is using a sand and gravel - say like a roadway subbase. This will cause very little problems if any over the short or long haul. If using local "clayey" or "silty" fill - this has to be addressed.

Testing - during fill placement, unless the new fill is highly stony, normal Proctor comparisons can be used. Use of sand cones, nuclear density gauages, etc. If the fill is large, you could consider "smart compaction" on the compactors to confirm stiffness of the fill placed. Fill lift thicknesses need to be addressed.

Finally - Get this all in writing, like others have suggested, by a geotechnical engineer

 

[mar2805]

Sorry for the long delay.
To answer some questions.

The virgin soil is made from rocks and dense sand
The fill would be made from sand and gravel, no clay!
We taldked to a geotechnical engineer and he also mentioned using nuclear density gaugaes to measure the compaction and the desity of the fill.
What I dont understand way not use SPT on this newly made fill in order to get some values on the bearing capacity of the soil/fill?

 

[EireChch]

SPTS are time consuming and costly, especially for only 3m of fill.

Take samples and do shear box testing, remove the gravels and your phi will be conservative.

Or you could assume phi of 33 if you ensure it’s well compacted. 33 is likely very conservative for a sand/gravel mixture fill.

For residential houses you’re not going to have bc issues on this material if compacted properly

 

[mar2805]

Thank you