Determining Settlement of Utilities under Crane Loading

[jsburk0]

I am looking for anyone who has had experience in determining settlement of utilities under crane loading. I have a client who is looking to move a large generator with a crawler type crane and is concerned about damaging the underground utilities. Any help/guidance with similar experiences would be appreciated.

 

[SlideRuleEra]

Ok, I done that. You will need to know the soil properties and a lot of other details:

Need the weight of the generator and any significantly heavy harnesses or lifting fixtures.

Need the full specs on the crane including it's lifting capacity, weight, size of the crawler tracks, etc.

Need to know how the generator will be handled by the crane, i.e. what will be the boom angle? will the crane swing while it is holding the load - that will change the load distribution.

The load distribution will NOT be uniform on the crawler tracks - need to make some reasonable assumptions for that.

Is the ground level, or on an incline - if so, how much?

What will be the duration of the load on any given spot? Perhaps a small number of minutes, maybe longer if there are delays.

Need to know the depth and properties of the of utilities (pipeline? direct buried cable? concrete encased electrical duct bank?) Also, need to have a realistic idea of how much settlement, if any, is allowable.

Once you have this info and have made necessary calculation and assumption you should get an idea of expected soil settlement.

IMHO, the best answer to your project is to take steps to minimize settlement. This could include the use of a crane with larger crawler tracks, or the use of (structural, usually wood) mats between the crawlers tracks and the soil. Maybe even a temporary soil surcharge over the path the crane will take.

Sorry, no easy answers... just a lot of assumptions based on engineering judgment and a detailed conservative examination of the entire move.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[oldestguy]

If this is a private emergency generator move, chances are the utilities for water and sewer are too far down to be of concern. It isn't just the settlement of the utility, it also will be the settlement of the area as soil compresses taking the utilities along with it. More likely the risk is breaking the conduits, not settlement. So, if this really is a high risk thing, you don't take any chances and bridge the area as indicted above. Is the job worth all that expense and grief, or can one just do the work that is common to avoid damaging pavements, etc?

 

[racookpe1978]

Yes, but the second (more dangerous!) half the same settlement question under a very heavy - and non-static!! - crane load is the settlement of the CRANE under that load. Particularly if only one side (or one end) of the crane begins to settle, but the other sidfe is on firmer grounds, or is on better soil (less wet, more compact, different type, different mix, a road itself, over a culvert that is not moving, etc.)

Then, if ANY substantial sagging of one side starts, the crane settles towards that side, the load on the boom shifts as the boom moves, and that load movement is TOWARDS the sagging (downhill) side. Feedback continues as more weight moves towards the downhill side of the crane and boom -> and the load collapses the crane, often turning the entire crane over and killing/hurting the crane operator because he cannot escape the cab.

1. Do NOT plan on moving this heavy a load by the crawler crane if you have ANY question about the soil being moved over.
2. Get a series of 4 sets of soil samples over the path of the crane: one to the left and right of the right-hand tread, and the set set of samples to the left and right of the left-hand tread. Sampling the soil between the treads will give you a nice sample, but there is no load there.
3. Once analyzed over a specific path for the crane or - better yet! - the heavy mover, do NOT allow the crane or heavy mover to deviate from that studied path.
4. At the end, where are you going to put the load, and how long will it be stored on what kind of surface? I have seen powerplant rotors, casings and turbine assemblies "sag holes" into even asphalt pavement when arbitrarily stored in the wrong place in a parking lot designed for cars and panel trucks.

 

[mudman54]

use crane mats