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Raft foundation

Raft foundation

Raft foundation

Hello guys
We are planning on studying a building with 9 storeys plus 4 underground parking lot . The soil layer which we will be constructing our raft foundation upon ( 10 m x 10 m raft dimensions ) is made of marl with limit pressure PL of about 25 MPa . This marl starts from a depth of -8 m and our raft anchor depth is at (-12 m )deep . All the soils above the anchoring depth will eventually be removed

My questions are :
1- How do we deal with such deep rafts in term of bearing capacity ? does the same analytical equations for shallow footings apply in this case ?
2-Does the bearing capacity calculated from say analytical methods or pressumeter test pertains to the vertical load divided by the raft area or should we divide it by the area afterwards ?
3-What about computing the bearing capacity using pressumeter results for this semi-deep foundation? i proposed to my colleagues to use load-unload cycles in the pressumeter test ?
4-The oedometer test should also have an unloading cycle by removing the same amount of effective stress at the depth of -12 m and then continuing the test ? and is it possible that after an unloading cycle in this test to have void ratio get about the initial value at the start of the test ?

Thank you

RE: Raft foundation

I took a look at your posts for the last 1.6 years and see you are relatively new to the field. This job appears to be major project where mistakes can really be serious. Even though you have an "idiot boss", it would be to the firm's advantage to make contact with an outside firm which is much more experienced for this job for advice. Sometimes using a firm from a distant area works out, since they may not be in competition. We all have done this and it does not detract from our reputation. In fact we developed some great professional contacts that helped on other jobs also.

RE: Raft foundation

Your building is 13 storey in total and approximately 260-300 kPa maximum loading.

As oldestguy said, your questions are advanced questions to be answered here. Thus, you should consult some firm. However, I can easily say your raft's bearing capacity is OK. Most probably settlements are OK too.

Lastly, what oedometer test? In marl?

RE: Raft foundation

yes in the bearing soil which is marl .

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