Foundation Works

[hiluxxx03]

I've got an instruction from our consultant that i don't understand the logic behind... based on the geotechnical report, we can excavate up to 1.5m from the natural grade level to achieve the needed soil bearing capacity but we must excavate 50cm more and backfill in two layers, 25cm per layer and compact up to 95% to prevent settlement. I really don't get why we have to backfill when we can have the 1.5m depth of excavation compacted up to 95% without backfilling or have the 2.0m depth compaction and have it compacted up to 95% and rest my footings there. as per our consultant, he said that soil bearing has nothing to do with settlement but what affects the settlement is the soil properties that's why we need to backfill a good material to serve like a spring that would receive the settlement... can anybody enlighten me regarding this matter? because as my experience, footings or foundations are rested on the natural ground level after excavation and no more backfilling only compaction...

 

[hiluxxx03]

*i mean 2.0m excavation and have it compacted up to 95%...

 

[ukengineer58]

Well it depends at what level you have suitable material. It sounds like the top layers ate unsuitable or at least filled made ground and not suitable. The reason to excavate it is to get matetial back in tha is compacted well. Hence the compaction layers. You won't be able to compact the 1.5m layer in one. You could just cast the foundation at the lower formation level but then you'd have 1.5 or more concrete. This sounds like a pretty standard and basic solution to me.

 

[cvg]

just excavate 2.0 and pour concrete and you should be good. faster, easier and safer than trying to backfill and compact in the trench

 

[BigH]

. . . and this is a double post.