## Bearing Capacity Calculation

## Bearing Capacity Calculation

(OP)

Hi there,

It's been over 7 years since my geotechnical class, please forgive me for my silly questions:

Q1: There are more than one equation available for calculation bearing capacity in textbooks? Is the Terzaghi's formula the most commonly used, or how do you determine which one is the most appropriate?

Q2: The ultimate bearing capacity equation involves phi' and c' (or Su for clay?). What tests should be performed to obtain these parameters for sand, and for clay respectively?

Q3: Should the parameters in the equation always be under the drained conditions, so are the tests performed to obtain the parameters?

Thanks in advance for your helP and patience.

ymchan2

It's been over 7 years since my geotechnical class, please forgive me for my silly questions:

Q1: There are more than one equation available for calculation bearing capacity in textbooks? Is the Terzaghi's formula the most commonly used, or how do you determine which one is the most appropriate?

Q2: The ultimate bearing capacity equation involves phi' and c' (or Su for clay?). What tests should be performed to obtain these parameters for sand, and for clay respectively?

Q3: Should the parameters in the equation always be under the drained conditions, so are the tests performed to obtain the parameters?

Thanks in advance for your helP and patience.

ymchan2

## RE: Bearing Capacity Calculation

Read some good books, including DM-7.1 and 7.2 for further insight on the rational methods for bearing capacity determination. There are correlations to SPT N-value also. It's quite hard to answer the "best" method without some context (i.e., regional geologic setting and local conventions).

f-d

¡papá gordo ain't no madre flaca!

## RE: Bearing Capacity Calculation

The prefix for each of these standards reflects teh Country/language used, i.e. in the UK it will be BS EN 1997, in Germany it is DIN EN 1997.

There is a real advantage to this, as it links the investigation and testing you have to do to the equation to be used in the design. Therefore when you specify investigaiton, sampling and testing it can be directly linked through the standard to how the data will be handled.

You can still use any equation you feel comfortable with but the standard requires that you provide a justification for it. It also defines three classes of structures to be built, and links what you have to do to the complexity of the design. Big changes in using these are that more 'traditional' methods of sampling, testing and calculating are no longer appropriate for more complex structures.

## RE: Bearing Capacity Calculation

## RE: Bearing Capacity Calculation

It does depend on the structure to be built but also when you go through the appendicies they are direct copies out of the text books 'we' have always used, presented as 'examples of how... can be determined'. I think I missed the point i was trying to make, which was IF you are in a Country which uses the EN system, then the standard identifies appropriate sources of information and methodology to use. For example when interpretting plate load tests to assess the plate settlement modulus, it refers directly to Burland (1969). Lots of the 'examples' refer back to Tomlinson, Burland, Bergdahl, US Army Corp of Engineers, etc... It forms a good starting point to research what options you have in certain cricumstances but does not limit the Engineer to use their judgement.

As mentioned above, the real difference (for the UK at least) is that samples taken with a U100 liner, or in alluminum U tube are now clearly limited as to what quality of specimen they are and what there appropriate use is.

## RE: Bearing Capacity Calculation

Thanks for the reply. I am in the US, and I am just asking these questions in the general sense, no particular project in mind. It seems like Question #1 was too broad to be answered.

Would you mind shedding some lights on questions #2 and #3 though?

Q2: The ultimate bearing capacity equation involves phi' and c' (or Su for clay?). What tests should be performed to obtain these parameters for sand, and for clay respectively?

Q3: Should the parameters in the equation always be under the drained conditions, so are the tests performed to obtain the parameters?

Thanks so much!!!

ymchan2

## RE: Bearing Capacity Calculation

Q3 - for sands and heavily overconsolidated soils, the drained analysis would be used (why for overconsolidated clays - because with the suction of water to counter the negative pore pressures developed on loading, the strength of the clays will decrease with time). For normally or slightly overconsolidated clays, you would use the undrained analysis (substituting Su for c'). If you could determine the actual porepressure response to loading, you could use the drained analysis but would need to be able to incorporate the porepressures in the analysis.

## RE: Bearing Capacity Calculation

The use of this was being proposed for the design of working platforms for tracked plant. The paper suggested that a settlement of 10% of the plate radius was appropriate in most instances. of note was that he angle returned from this paper was generally higher than a correlated SPT N value, a less conservative approach but a specific assessment of the actual ground in question.

I have not used this approach in the design of permenant foundations, but I have found it very useful in instances where there is a limit of information whihc has been provided for review. Tou also need to recognise that the zone of influence from a plate test is limited.

## RE: Bearing Capacity Calculation

## RE: Bearing Capacity Calculation