Plate bearing test - Crane Outrigger Loading - Modulus of Subgrade Reaction

[Eng9876]

I have been given a plate load test to try and make sense of in preparation for a crane lift. The worst case load on the outrigger is 60Tons/ m^2 using a 2mx2m pad.

My initial observation was that the test has only been carried out to 30tons/m^2 (using a 450mm diameter plate) and we are loading 60tons using a 2m^2 plate.

The test results show only the 'K' value at the 30T/m^2 level. (the K value turned out to be 45t/m^2/mm)

My question is this:

1. Am I right in saying I need them to test for at least 1.5-2 times the applied load in order for us to determine the settlement of the outrigger pad through interpolation and not extrapolation?
2. Is the approach of using satisfactory settlement criteria to an outrigger pad (say 50mm or 2 inches)to work out settlement the right approach for a crane lift. If the settlement is too much then my approach is to do some remediation to the supporting ground until satisfactory settlement is achieved. (I am sure it is, but am asking as I have been told by a few engineers (none qualified) this is the wrong approach and I should just take the k value of 45t/m^2/mm as being the 'Bearing capacity' (as this is what they have done in the past) and the lift is good to go on the k value of 45. - I think this is wrong information and feel that I can't really do anything with the data as I can't interpolate from the results as the test hasn't been carried out to large enough values).
3. Can I work out a bearing capacity based on the section modulus of 45t/m^2/mm (settlement 0.7mm?).

Any advice would be appreciated!

BTW-The company have always used plate bearing tests for the ground tests for crane lifts.

 

[Eng9876]

Just to clarify, the crane loading is 240tons. Giving 60tons/m^2.

 

[SimpleJohn]

What is your task? Are you trying to determine settlement of the crane pad, or determine the allowable bearing capacity of the site for the lift?
The K value you previously determined will be the highest you could expect, as higher loadings will generally encounter higher increments of settlement. That value "could" be used for your estimation of settlement, given some degree of estimation. However, if you have not independently calculated a bearing capacity for the site then this test is useless. You are correct to request a proof test to 1.5 or 2X the design load. Even then, the results of the site investiation should be used to calculate a bearing capacity for the actual size & shape of crane pad used. One can not extract a bearing capacity of a soil/foundation from a subgrade modulus.