Angle of pressure distribution

[GeoGrouting]

A very heavy crane is going to work in a site with the subgrade bearing capacity of 100 kPa. Granular fiil materials have been designed to transfer the crane load to the subgrade. We ideally want to spread the load as much as possible. Is there any relation ship between the gran size distribution and the spreading angle. The spreading angle is usually 30 to 45 degree but that would not be sufficient. What is the range of spreading angle for granular crushed fill materials Thank you

 

[csd72]

Geogrouting,

You either need to use spreader plates under the crane outriggers or use a properly designed crane platform on piles or similar.

I would NEVER use more than a 45 degree spread in granular material and would always try and use 30 degrees.

Cranes are not things to be underestimated as a sudden settlement of even one inch could cause a load to swing out of radius and lead to sudden crane failure.

 

[GeoGrouting]

Further to the comments by csd72, it would be desirable to know what type of fill materials could enhance a spread of 45 degrees. Seems crushed aggregates would be more appropriate. What would be the required gradation and particle sizes to attain the 45-degree spread? Thanks.

 

[Riggly]

Here are some further clarification I would like on this situation. i) Why is up to 45 deg. spread insufficient? ii) Are you assuming that all the loads of the crane would spread out based on the spread of the material? iii) Where is the load of the crane applied in relation to the edge of you stone fill? What is the applied crane load, and over what area is the the point of application?

I agree with csd72 that 45 deg is a sort of upper limit, but to answer your last question, it seems that you will need some kind of reinforced base (geogrid reinforced) and wrap the edges so that the granular material don't keep falling off.

 

[GeoGrouting]

This is for a hydromill crane. The subgrade bearing capacity is insufficient and we want to take advantage of spreading in the pad granular fill. So I am interested in knowing which gradation produces the maximum spread (i.e. 45). I can go up to 1.2 m fill. I hope this explains what you asked. Thanks.

 

[Riggly]

So you considering the spread of the load (which is related to angle of internal friction) rather than the angle of repose of the material?

A few factors affect the angle of friction- not just gradation (type of material, angularity, compaction level, etc). Several diffent gradation may meet the 45 angle criteria depending on the in-place properties as listed above. A reinforced fill material, with geogrid, can better able to spread the load over a wider area and reduce the applied pressure to your foundation, or use the appropriate spreader plates as suggested by csd72.

 

[GeoGrouting]

The spreader plate does not seem applicable because the hydromill has to maneuver on a relatively vast area, as far as I understand spreader plate.

Which materials have a better load distribution, e.g. minus 19 mm or minus 75 mm and what would be the effect of silt sand gravel contents. Thank you.

 

[csd72]

as riggly has suggested I would suggest using a geogrid or a geotextile at the base if you want to achieve the 45 degree spread.

You will of course have to design this to ensure that it has adequate strength and friction against the soil.