Selecting excavation equipment

[DFrancom]

The Caterpillar Performance Handbook and the Corps of Engineers use siesmic wave velocites to help determine the type / size of excavation equipment needed to excavate a given soil. Does anyone know of other methods to help determine what equipment will be necessary to excavate "hard" soil using more readily obtainable site information/data like the SPT N-value, soil density, etc?

 

[dtrisler_imported]

The UBC has ranges of SPT N values correlated to ranges of shear wave velocities. These could be considered very rough estimates. Check the soil types in Chapter 16. Better yet, see if earthquake hazard maps exist for the site vicinity. If so, they may have representative shear wave data for different geologic formations.

 

[DFrancom]

dtrisler,

Thanks for the information. I was not aware that the UBC had such a table.

 

[WideMike]

Suggest that you begin accumulating production data on this project for future use. Nothing better than your own actual production figures to estimate future work. Regards. WideMike

 

[Focht3]

Correlations between rock/"hard soil" rippability and SPT blow counts scare the hell out of me. Even looking at RQD and % Recovery can give you dangerous answers if you don't know the geology. [blue]WideMike[/blue] is right on target - develop your own judgment on this topic.



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[DFrancom]

The project is nearing 90% completion on the design and will be going out to bid fairly soon. Our A/E firm had a subsurface site investigation performed, which provided SPT blow counts, standard proctor data, PI, and moisture content along the pipe alignment and other excavation areas.

Our worry is that the successful contractor will ultimately have a difficult time excavating and will file a "differing site conditions" claim against us. We want to insure that we have provided them enough useful data that they will be able to accurately determine the effort and equipment needed to perform the excavation. This way we can avoid any claim. We also want this data so we can determine the cost of excavation based upon the effort and equipment needed.

It still appears that the only direct correlation between "excavation effort" is through seismic velocity (Corps of Engineers and Caterpillar manual).

Thanks to those above for their input!

 

[Focht3]

How about some test pits to check out the rippability in selected areas of the site?



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[jheidt2543]

A couple of thoughts:

1. What would be the basis for a Differing Site Conditions claim? If the subsurface investigation fairly represents the actual conditions to be encountered, on what basis is a claim filed? Actually, I suppose you can file a claim for anything, the question is does is does it have merit and will it prevail.

2. Prequalify your bidders. Make sure the bidders have had experiance in the work you are bidding, including working in the same soil conditions.

 

[cvg]

If your material qualifies as "rock", the excavation should be bid as rock excavation. The borings should indicate if it is rock (put the boring logs on the plans) Or, ask the geotech to provide an addendum to the report with his opinion of the rippability of the material or for recommended equipment to be used in excavation. I typically ask for this information in reports.

 

[KRSServices]

If the project is ready to bid and 90% completed on design, you should have a very good idea on the types of soils that are going to be encountered on the job. Assuming you or your firm are experienced on this type of job and/or terrain, why are you so concerned about the degree of difficulty the contractor may experience? If the tender package includes a geotechnical report, complete with soil logs, then it is up to the contractor to bid it accordingly. Your task will be to provide an accurate pre-tender to your client.

If you are really not sure, there is no harm in contacting a reputable contractor to provide some insight into the job. Although he'll likely be bidding as well, it could help you in your estimate.

Regarding the claim, now is the time to write an appropriate clause(s) in your contract to minimize the claim. That is unless, of course, you have insufficient information for bid and the contractor has to guess. Contractor's are notoriously bad guessers.

Your original query was specific to the types of equipment that will be required. Again, as the project engineer either you or your firm should have some ideas int terms of an estimated value. The contractor will determine what equipment they will use based upon thier bid. It is not the responsibility of the engineer to specify the type or make of equipment to be used on a job.

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