foundation bearing capacity site tests 2

[scut]

In general, we come across a variety of soil types. I am involved in inspecting foundations for two storey houses prior to pouring of concrete. Is there any practical site test which can be carried out without laboratory equipment, to determine the bearing capacity of the soil.

 

[ishvaaag]

The proper thing requires geotechnical investigation have been carried on far before placing concrete, and this is as well true for design build things, that must mean better logistics, not disdain of required practices. Then with time the classical tests can be executed and the report made and you have no reasonable doubt more or less the thing is going to work without relevant problems.

If occassionally you find some irregularity, this you solve normally by piercing by force if piles, or bridging to other capable members.

But soil capacity being in doubt at the time of placing concrete is not the proper way to go. In any case if brought under proper logistics and a daily practice, all the geotechnical test become simple, be penetrometres or plate loads. Some lookup to charts or tables or input to a mini PC program and you have your capacity.

 

[emmgjld]

I normally do what you are asking, determining an approximate bearing capacity within the 'open excavation', ONLY UNDER CERTAIN CODITIONS. Some sort of penetration test or in-place soil density testing is usually required BUT

You MUST understand the general soil profile of the area.

You MUST understand the locations of the general and specific Water Table and the seasonal variations.

You MUST understand what actually determines the particular soils' Allowable Bearing Capacity (Shear, Consolidation, Swelling Characteristics)
You MUST understand the soil profile, ground hydrology and the potential of changes after development & landscaping.

You MUST know the characteristics so well that your penetration testing, possible in-place density testing and your visual assessment of the site and the area are confirming what you already know.

ishvaaag is right in that the normal and proper practice is to know most of the answer before construction begins and then appropriate observations and field testing is performed to 'prove' the knowledge.

 

[nbryan]

The answer to the question is NO.
Unfortunately, I've had the opportunity to visit properties
where poor soil conditions were bridged with compacted fill.
Unfortunately, the foundation sytem was bearing under the fill.

 

[Ron]

The answer to the question is....well, maybe!

If you are carrying out inspections in similar soil conditions, you can develop correlation tests using a hand-held cone penetrometer, or probing with a probe rod. Check with a local geotechnical engineer...they have likely done this already.

Plate load tests can be used for estimating bearing capacity. They are relatively expensive to run and are site specific in their results; however, familiarity with local soil conditions can lead you to develop a level of comfort with other correlated tests. Keep in mind, the structures you have described are relatively lightly loaded, so unless you have significantly adverse soil conditions at the footing bearing level, the bearing pressure and capacity are likely not that significant.

Further, don't place all your emphasis on bearing capacity. Residential structures are rarely compromised due to bearing capacity failure....they are much more likely to be distressed by underlying soil conditions that result in settlement or from poor construction practices.