Bearing Capacity Test 1

[abusementpark]

It is very common for a testing program to be implemented into a deep foundation design to gain economy. However, is something similar ever done for shallow foundations with regard to bearing capacity of soils?

Is there a common bearing capacity test that can be performed for footings?

 

[BigH]

Plate load test - although it is much smaller than most footings. Bearing capacity for shallow footings, in my view, is not the best way to choose a design value - the actual bearing pressures will be settlement controlled. Plate load test not appropriate for clay, in my view, due to consolidation settlements.

 

[msucog]

during the subsurface exploration, talk with the geotech. aim for additional soil test borings and increased sampling frequency depths to improve the confidence of the exploration. and as bigh mentions, settlement will usually drive the allowable bearing pressure recommendations. so i'd usually obtain undisturbed samples and perform consolidation testing as part of a settlement analysis. also, provide as much information as you can related to loading, footing spacing, etc. this will help the geotech sharpen their pencil a bit. as i mention, discuss this with the geotech on the front end preferably at the time they are putting together pricing. specifically mention that you are trying to maximize efficiency of the footings and are looking for refined recommendations regarding the foundation support. there are other options available so hire a "good"/competant geotech and discuss the project with them thoroughly. the effort with be well worth it to the project.

for example, a 'typical' exploration where the client wants lowest bid will get a knee jerk reaction exploration. bearing pressures will be 'typical' for the geology (say 3ksf) as long as nothing funky shows up in the borings and loads are not very large. in reality, with a little extra money that 3ksf could easily be 4ksf...again with money to perform additional field work, lab work or engineering to justify the recommendations. if you want to go far to the high end and throw lots of money at it, you can buy yourself a high end foundation design. as you get 'higher end' there are many other aspects/variables that must be considered and documentation to justify the recommendations. just like with designing structures, there are always other ways to design say a CIP wall. change the dimensions and orientations, use better materials, use select backfill, increase this and decrease that, etc etc...or you can default to the tried and true 'quick' design. for most applications 'tried and true' is sufficient...other times, you want to go with an in-depth design to push the envelope a bit but it takes design time and additional testing to make it happen.

 

[mudman54]

in practice, an indirect method is common. this method classifies the soil based on standard pentration or cone penetration results and then compares it to the building code presumptive bearing capacities. for example, massachusetts and city of new york have excellent building codes which identify the material types. the bearing capacity "test" is commonly based on observations and judgement. take a pocket penetrometer with you when you climb down into the footing to be sure it is a hard clay; sand may be more difficult to classify without such a handy test. if your boot sinks in, maybe you do need a soil load bearing test which may include a plate load test or a california bearing ratio test.

 

[fabianjm]

You can do static loading test the same way for pile then the ultimate bearing capacity you can compute based on the load-settlement curve by using Chin's,Manoppo&Koumoto,P-Y Curve,etc..the results can compare with indirect data to make sure..