Raft foundation

[BlackMask]

Hello All,
. I am constructing a g+2 house. As a result of soil testing , i was asked to go in for a raft foundation as the soil is loose.The engineer has suggested a 8 ft excavation on which a 2ft boulder, 6 inch pcc and a 2feet raft will be put. The columns will be raised on the raft. I would like to know if this is ok and the steel inforcement details for the same.

Thanks
BM

[girishd]

@BM,

Just like when doctor suggests a big procedure you take second opinion, you should do the same for this problem too.

My Structural Engineer is doing Ph.D in con-conventional structures. He studied our soil testing reports and suggested foundation depth. PM me know if you need his contact.

[Nivas]

how much was the sbc ?

[BlackMask]

The report is as below:

bore no values. Sbc T/m2
bh01 5. 5.0
. 40. 20.0
bh02. 6. 6.0
. 31. 20.0

bh03. 5. 5.0
. 40. 20.0

[BlackMask]

Pls read it as boreno. nvalues. Sbc (T/m2)
. 1. 5. 5
. 40. 20
. 2. 6. 6
. 31. 20
. 3. 5. 5
. 40. 20

[Nivas]

you did a very good thing going for the SBC test , in fact it should be a safe practice when buying the site as well.
5T/M2 is low Bearing Capacity , your site could be a marsh with low water table or Unmanaged landfill , you might have to go with raft as suggested by your engineer. If you carefully read your remarks on the test report \ inference,it might have suggested kind of foundation or at least mentioned not suitable for Shallow foundation. Or you can call the test agency and get their opinion free of cost.

[pvn]

Is this 5T/M2 or 20?

regards

[BlackMask]

The table has 2 n values for each bore point. For a n value 5 it is 5t/m2 and for a n value 40 the sbc is 20t/m2.

[BlackMask]

Also the first set is for a depth of 1.5 m from ogl and the second set if for 4.5 from ogl.