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procedures for foundations on fills

procedures for foundations on fills

procedures for foundations on fills

(OP)
I like to know the procedures to make foundations on filled
soil. How to determine the bearing capacity and other soil parameters for the design of foundation.

RE: procedures for foundations on fills

Make a search in Google for

Considerations When Building on Landfills
Prepared by:
Tom MacDougall

In general, poorly consolidated fills have a significant time component to its behaviour. Floating foundations (with the need to equilibrate weights and uplift) may be convenient.

More frequently and if feasible, deep foundations are better. Always consider then the further settlement of the fill loading through friction the piles.

Intercalation of permanent jacks may help to keep the main structure as intended upon variable settlements, but this is not be going nor cheap nor it is very clear how to adapt ordinary structures and foundations to these contraptions.

Don't forget to check a pair of books on foundations.

RE: procedures for foundations on fills

Your considerations will be dictated by the depth and character of the fill material, as well as the geotechnical properties of the soil beneath the fill.

In general, the issues are:
1)  Make sure the fill was placed over competent material (this is done by a geotechnical investigation)
2)  Determine the character and properties of the fill (lab testing for classification, in-place density testing for compaction, plate bearing tests if appropriate for indications of bearing capacity)
3)  Evaluate these concurrently with respect to your building loads

RE: procedures for foundations on fills

Usually the fill soil is compacted to 85-100 percent of the maximum density as determined by the Standard or Modified Proctor compaction tests.  If you know this to be true in your case and the soil is granular, the angle of internal friction of the soil may be estimated indirectly from published relative density charts.  Typically, if your relative density is in the 85-100 percent range, the angle of internal friction for the soil is usually up around 40 deg.  Bearing capacity can then be calculated in the usual manner. To obtain this data directly, samples should undergo a direct shear test, triaxial test or relative density test.  

If the soil is cohesive, samples should undergo an unconfined compression strength test.  From the unconfined compression strength the bearing capacity can be calculated.

If the fill soil was not placed under field control, it should not be used to support structure foundations without first taking soil borings and performing tests (as recommended by Ron above) to determine the allowable bearing capacity.

RE: procedures for foundations on fills

Also, for fills a frequent consideration is the attainment of terminal settlement.  This is ascertained from a planned settlement monitoring program.  
For cohesionless soils, settlement is in the main immediate while for cohesive soils, the consolidation characteristics will provide a guide for the determination of the settlement monitoring program - long term settlement.
A note of caution though, soil science is not an exact science.  Theory always gives conservative results.

For a fill, settlement results from both the fill material (duration dependent on fill material), depth/thickness of fill, thickness and depth of underlying clay layer - from a sub soil investigation survey.

The choice of foundation type will depend on the type of facility proposed and loads in service.
NB  Hydraulically placed, well graded granular fills can support light structures - for which a pad foundation may be proposed.  For critical facilities however, for which settlement is a key consideration, then a pile foundation is the answer.  Even for piles, ongoing settlement gives rise to negative skin friction.

Frequently though, it is often the practice that fill grounds serve only to provide a working platform subjected to minimum service loads - roads, walkways etc.


kay

RE: procedures for foundations on fills

I have heard there have been recent studies on the long-term consolidation characteristics of deep compacted fills with respect to negative performance.  Can anyone out there help me out with any sources.

RE: procedures for foundations on fills

hi friend,
 To consturct the foundation on fill it has been always a
 challenge..... but one  can  constuct a safe structure on it.
     my filling is that first of all you should do some SPT test and get the idia of bearing capacity of soil ... second generally in fill material some oxidizing materials will always be present so it makes  the water, acidic, presented in soil mass... which can destorts the foundation material. to design the foundation is as usual.. what procedure is following as a standard. but you should always consider secondary consolidation while designing. also if you are going to place precast pile so my suggestion is that use epoxy coating on plies before installing.
       i think i gave reply from my best level.
  byebye friend

RE: procedures for foundations on fills

Just a word of caution regarding foundations on fills. Fills compacted dry of the optimum moisture content are prone to collapse settlement upon inundation (e.g. raising of groundwater level or excessive surface runoff from heavy rain). Therefore, proper control of compaction is very important.

RE: procedures for foundations on fills

Consider a pier system (into load bearing soils) and a raised wood floor (reduces burden) to minimize differential settlement problems.

Cheers  

RE: procedures for foundations on fills

....and do check that there are no gases being generated within the landfill site; gas memebrane and vent system may be needed under the footings and ground floor slab area.

RE: procedures for foundations on fills

For clean fills (no bricks, concrete, asphalt, broken bottles, etc), our firm performs a standard geotechnical exploration and we treat the fill just like a native soil.  We have two concerns at that point.  One is the variability of the fill encountered in the borings.  If it is uniform, great.  If it is variable, we choose roughly the worst results as the basis for analysis.  The other concern is consolidation of the native soil below the fill.  We treat the fill as a surcharge weight and evaluate the settlements accordingly.  A consolidation test will take out some of the "engineering judgement."

Regarding collapse potential...  We have only seen it in granular soils.  And, the collapse potential test (ASTM D5333) has shown that at whatever moisture content 95% of D1557 is achieved, the collapse potential is slight.

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