Crane Assembly Hardstand Check

[ronanon]

Hello,
I am wondering if I could get some help with a problem I am currently having. I am looking for a standard procedure for testing a crane assembly hardstand.

To explain, the cranes my company use to assemble wind turbines, i.e. Liebherr LTR11200, exert a significant pressure through the bearing pads to the hardstand. We specify a minimum bearing pressure of 220kN/m2 over an area of 45m x 20m (sorry, Metric values but the concept should be the same). As subcontractors carry out the work, I need to be sure that this bearing pressure is achieved with a method that is simple and economical.

The data I do have, SPT values so I can approximate the sub-grade bearing, i.e. SPT value x 10.
CBR value, I can check whether the CBR value is acceptable. What would be an acceptable minimum for this purpose?
I am not comfortable with equating CBR value to bearing as the CBR value is only local to the material used as surfacing.
I will also receive the sub-grade CBR value.

I know of the plate bearing test, I assume this is the procedure that could be used. But I do not have an exact procedure for this test on-site.

Does the plate test equate a ratio of youngs moduli to measure the stiffness, if not what is this test?

Also, one small thing, Youngs Modulus is a measure of the stiffness. What stiffness is required to reach the values of bearing needed.

If there is any further recommedations I would be most grateful. Thanks.

 

[BigHarvey]

You will find procedures for the design of working platforms for crawler cranes on the following organizations websites :

Federation of Piling Spacialists ( FPS ) in UK
SOFFONS in France

 

[ronanon]

Thank you for your reply, I will review the information over the coming days.

 

[iandig]

BS EN 1997-2 (Eurocode 7) Annex K discusses a range of methods for assessing plate load test results, which in turn can be used to assess the undrained shear strength, or plate settlement modulus. The equations are no different to many soil mechanics textbooks, but they are encapsulated in a European Standard.
The FPS dcoument on working platforms for tracked plant referes to the BRE document BRE BR470 "WORKING PLATFORMS FOR TRACKED PLANT". The process of assessing the bearing capacity of the ground uses a more complex set of equations than some parts of Europe, but once added into a spreadsheet can assess the requirements of the working paltform very quickly. The basis of the assessment using the BRE BR470 guidance is either by undrained shear strength for cohesive soils or by angle of shearing resistance inferred from SPT data. A very recent paper on the design of working platforms (Ground Engineering magazine February 2010, pp29-31) proposed an imporved method of assessment using plate load tests to calculate the ultimate bearing capacity of the ground, then by using a nominal FOS converting this to allowable bearing pressure and/or angle of shearing resistance which can then be used in the BRE BR470 calculations to provide a more 'ecconomical' design (i.e. thinner).
BRE BR470 requires the designer to check the ground to the full depth of influence from the tracked plant, and for this assessment uses the 'characterisitic' dimensions of the tracked plant, which in turn are calcualted by following the FPA process.
Can plate load tests be used - yes if the ground is homogenous and increases in strength with depth, or any variation in strength can be assessed as seperate layers.