raft foundation test

[Alexphd1]

Before we start setting out the eps has any body done a load test on the hardcore? It has been well rolled out but my archietect thinks its a good idea for peace of mind.

 

[PeterW]

40 minutes ago, Alexphd1 said:

Before we start setting out the eps has any body done a load test on the hardcore? It has been well rolled out but my archietect thinks its a good idea for peace of mind.

 

 

I thought the whole point of the EPS raft foundations was they were very low ground pressure ..??

 

I've just done a quick fag packet calc from my BoQ and I reckon a 3 bed that is built with standard construction has around 90 tonnes of materials in it. If you double that for good luck, my 90sqm building would exert 2 tonnes per square metre, or 0.2kg/cm2

 

That isn't exactly a lot ..! The bearing capacity of compacted gravel is >300KPa that equates to 3Kg/cm2, the loading applied by the foundation  is vastly less than the bearing capacity. 

 

Who has designed the raft out of interest and who is providing the warranty..??

[IanR]

Is hardcore a suitable sub-base? As it's generic term I'm assuming it can't be certificated in the same way that say Type 1 can be.

 

Or are you then putting a sub-base on top of the hardcore, and in that case you need to ensure the hardcore has the minimum bearing capacity stated for the foundation, which for mine was 100kN/m2

 

52 minutes ago, Alexphd1 said:

load test on the hardcore? - my archietect thinks its a good idea.

 

 

What's more important is that you have a "chain of custody" from Engineering specification to products used to ensure the Engineer's Insurance covers latent defects. (Unless the Engineer is overseeing the work).

[Alexphd1]

Approx 300mm type 1 then 150mm of clean bigger stone (think 50-80mm dont have spec in front of me) topped of with 50mm depth of fine stone. We have followed Tanner structural drawings ie compacting every 150mm etc but my architect has suggested getting it tested for "peace of mind".  I feel this is not needed. We are not bothering with a structural warranty but obviously we are going through the local building control as needed for a completion certificate. 

[IanR]

Ah, OK, you were being non-specific when you said "hardcore".

 

While there's probably a minimum bearing capacity in the spec for the soil under the type 1, there won't be for the type 1 itself, so you've not got a figure to test too to give you the peace of mind your architect is after.

 

The Type 1 spreads any loads applied on it out to a wider foot-footprint of the soil beneath at an angle of 45 degrees, as does the EPS. So a 500mm wide ring beam, sitting on to 300mm of EPS and 500mm of aggregate, theoretically passes its load onto a 2100mm width of soil.

 

The requirement for compacting the aggregate is to just ensure the load is passed on and spread wider, but doesn't itself come with a required load bearing capacity.

 

 

[Declan52]

You could do a dpc test that will plot a graph showing the bearing pressure. 

http://www.lab-quip.co.uk/dynamic-cone-penetrometer-dcp

Any site investigation company will do this easy enough. 

 

Also done a slightly different test where we jacked up a land rover defender with a steel plate under the two jacks lifting the Jeep up. The smarter guys in the office where able to work out the pressure the Jeep put on the plate and how far it sunk over the space of a few hours. Easiest days work I ever done!!!

[Alexphd1]

sorry IanR I should have been more clear.

that's the test the architect spoke about. I think he just been very cautious.