How is compaction done for fills under slabs in buildings 3

[IJR]

I was just curious. I know that rolling is used to compact soil fills under road pavements and slabs on grade covering large area. Someone told me that in buidings you would use ramming.

I need further info on this whole thing, including typical subgrade materials used.

I will appreciate if you help

Thanks

 

[KAM_imported]

I'm not sure I understand your question, but any fill providing structural support to something bearing above should be placed and compacted in controlled lifts. Compaction should be verified by field density testing. The thickness of each lift will be a function of soil type and the size (weight) of the compaction equipment used. If heavy rollers are used to compact relatively clean sands, fill lifts can be 12" thick. In confined areas, where walk-behind vibratory plate or sled compactors are normally used, fill lift thicknesses should be reduced to 6". Sandy fill soils are usually compacted to at least 95% of ASTM D1557 (Modified Proctor) density. It is usually desireable to utilize relatively clean, inorganic, non-plastic sandy soils as fill materials as they are relatively easy to compact, not overly moisture sensitive, and are of low compressibility. Selection of a fill type at a particular site will depend on what is locally available. The type of equipment used to compact fill soils is a function of soil type: vibratory drum rollers or bulldozers can be used to compoact clean sands, rubber tired rollers are used to compact silty or clayey sands, and sheepsfoot rollers are normally used to compact clays. Compaction of sands requires vibration and pressure, while compaction of cohesive soils requires high pressure. Vibration is of no benefit when compacting clays.

 

[JAE]

Good comments by KAM.

Ramming perhaps refers to a pogo-stick like compaction device known in our parts as a "jumping jack". It is primarily used for hard-to reach areas where a vibratory plate would have difficulty in maneuvering around.

Subgrade materials used: There is really no typical material used as it depends upon your locality, availability of materials, and quality of in-place soils. Generally, you will find most engineers/geotechs will specify a removal of all organics from you subgrade, a discing up of perhaps 6 to 12 inches of material with re-compaction to 95% optimum density. Then any fill may be added using either a well-graded granular material or existing soils from the site if they are suitable. Finally, a uniformly graded granular material is placed as a direct subgrade to the slab. This material provides a capillary water barrier under the slab to minimize moisture movement from the soil to your slab. Compaction, again is per KAM's response.

 

[cvg]

assuming it is a larger building, the foundation will probably NOT be on compacted fill at all. The foundation will be excavated to competent material or it will be on piles.

Chuck
cgopperton@stantec.com

http://www.stantec.com/

 

[sc]

In our area (for residential and "small" commercial developments) we use a loamy sand that compacts suitably under wetting. The material is placed and levelled, then soaked over approximately two days, then allowed to partially dry.

This gives a suitable density of material for constructing on.

Regards

SC
(Mildura, Australia)

 

[IJR]

sc, if I didnt get you wrong, you mean no mechanical compaction, only wetting-drying action. If this is true I am really interested in the subject.

Thanks in advance

 

[longisland]

IMHO, it's a bit tricky to use a roller compactor to do compaction if the ground beams
are cast.
BTW, I get the 95% MDD part & material may vary based on locality. So what's the criteria for selecting a fill material? Insitu CBR value at the source? plasticity index?
sieve size of the granular?
If the ground slabs are supported by ground beams, the soil beneath isn't carrying
any load. Is it still necessary to compact to 95%mdd, if so why & if not then what's the
appropriate treatment?

 

[ishvaaag]

Provided compaction is feasible, compaction is good and we advise to be made under slabs in the ground and even under foundation beams. This helps just a bit ro reduce movement. I have seen it be made even without our ordering it by contractors, both with a small roller (for cases where single piles under columns are later joined by one doubly reinforced slab, a practice we have followed for 1 story (on the ground) parkings sometimes, or by the "jumping jack". This must be most beneficial locally than at building level, since general settlement of the building is quite impervious to the kind of foundation used, except if very stiff for the size of the building.