Ground beams question

[Gus14]

In normal practice ground beams are at the foundation level to support the ground floor partition load and prevent differential settlement. But if the foundation depth of embedment is very deep, for example 3 meters, the ground beams would be about 2 meters above the footing. In this case is it necessary to provide another tie beam at the foundation level to prevent differential settlement or not ?

 

[HTURKAK]

If the foundation depth ( above the footing ) is more than 2.0 m., it is better to have basement floor. With this set up, the effective stress will reduce so the settlements..

If you do not want to have basement, you are expected to extend grade beams to top of footings and make filling.

If this is a real quetion , pls post some details and more info. to get more helpful responds..

 

[Gus14]

I have a sand soil with an allowable bearing capacity of 200 KPA at 2.5 meters depth of embedment. The clear distance between the ground beams and footings is 1.55 meters I attached a quick sketch. Do you think I should extend the ground beams down to the foundation level in my case ?
I couldn't find information or guidance about ground beams location and function in any textbook.

 

[HTURKAK]

Dear GUS 14, the sketch that you provided does not give any info. regarding the ground floor level, grade, size and no of storeys...Pls provide more info.

You are saying allowable bearing capacity 200 kPA at 2.5 depth .. What is the reason that you need 200 kPA ? Why not use 100kPA so the foundation depth will be say 1.0 m , and grade beams with ht 80-100 cm ?..

 

[Gus14]

Sorry for the late response, well this is a three story residential building, the building area is ( 26 m x 12 m ). The ground floor level is (+0.15 meters ). Most columns approximate loads are 750 kn, three columns have 1400 kn and four columns carry 200 kn. Using 100 Allowable bearing stress means that the net stress is 65, which would require unreasonably large footings.

 

[HTURKAK]

Dear GUSS 14,

IMO, it is not reasonable to excavate around 3 m for foundation excavation and use shallow depth grade beams , tie beams and backfill ..

You have a lot of options,

- Assuming the loose sandy soil at uppermost 3-4 m, you may consider soil improvement ( jet grouting , soil exchange ..etc..)
- You may consider inverted bowl type raft
- Grid foundation with say grid beams 30/80 and footings having depth 80 cm at nodes
- Continuous footings..

Etc..if you post the plan you may get more helpful responds..