Foundation recommendation report 3

[Geosubhtech]

Hello,

I am working in a project of eleveted corridor of 14km length. So boreholes were planned in 75 m intervals. The span lengths are varying from 26m to 80m. So the client is asking for a separate report for the consideration of Boreholes for the calculation of pile capacity for each pier. So i need help regarding the documentation part. Any help regarding how to write up the report will be very useful.

Thank you.

 

[EireChch]

Jes where to start. It is a very open ended question. One thing that is crucial is that you understand the ground conditions and their potential variability in the vertical and horizontal directions. I would have an experienced geologist develop geological long and cross sections.

Boreholes been spaced at 75m. If piers are spaced at 35m, is there a chance that you have a pier that doesnt have a borehole within 35m? I would have ensured that boreholes were located beneath proposed piers...

 

[PEinc]

I agree. Try to get the pier layout and do a boring at each location.

http://www.PeirceEngineering.com

 

[oldestguy]

Depends on budget and common sense. I'd go by the EireChch recommendation.

 

[dik]

I would suggest it depends on the variability of the results... @ 75m, if you have 300 boreholes that are nearly identical, there is little to be gained by doubling the number of boreholes. You just have to realise that things could be different between the hole locations.

Dik

 

[fattdad]

I'm not sure I see the reason to drill at each pier location. I do see the reason to describe variability in the stratum(a); however.

That said, working for a state DOT if there is federal money, we will drill at each pier, 'cause that's what their program requires.

f-d

ípapß gordo ainÆt no madre flaca!

 

[oldestguy]

I used to be the first "soil engineer" for Wisconsin DOT back in the 50's. There was a reason for "drilling at each pier". It was due to almost all the jobs were river crossings. Due to erosion and deposition there could be significant differences even within each pier. Drilling first through existing bridge decks or under overhead power lines did have an effect on where to drill. I'd bet most Geotechs these days would not know what "wash and chop" means, or 50 feet a day was a good one or who mister Gow was. However, with the Interstate and the overheads not being in river crossings, and knowing the general geology, we could adjust the number as the job went along, but always at least a few at each structure. One thing I found frustrating was the need for preparing for the future, with possible expansion or some utility digging a trench next to a footing. I did get a structural engineer chief to agree to spread footings on one job. Bedrock was at pile cap grade. Otherwise piles were the rule even if you had to drill a hole first.

 

[Mad Mike]

Sounds like you should be running a Preliminary investigations contract and following it up at a later stage with the Detailed investigations.

For the Preliminary drilling you could put down say 1 borehole every 250 - 500m; try place as many as you can at structural elements so the field data can be reused in the detail design. Understand as OG says, that all river crossings probably need to be drilled. Put down a good number of inspection pits in addition to the boreholes.

Setting up a detailed investigation of this scope is incredibly tough without having any preliminary data, even if the soil conditions are relatively well documented.

All the best,
Mike

 

[Ron]

You indicated an elevated corridor. I'll make the assumption that this is in an urban area, or at least urban to suburban. Given that assumption you likely have a plethora of geotechnical information from a variety of sources. Start with a paper search and fill in with boring information. I agree with F-D and dik...not sure you need a boring at every pier unless required by the client.

Also agree that a preliminary and final phase of investigation should be done. From those develop a good subsurface profile, using the preliminary subsurface profile to dictate the final geotechnical phase. The last part is the evaluation of your data. The data won't tell you everything....you'll still have to use engineering judgment to develop the recommendations for the foundation system.

 

[Geosubhtech]

Thank you everyone for your replies.

As Ron said we did a preliminary investigation at 450 m interval and detailed we did at 75 m interval. Data came mostly similar not varying much. There are all total 800 piers. if we go for each pier each drill it will not be economical. and below 10 piers are falling on the banks of river.
So, by engg. judgement only we have to decide i think if conflict comes in between adjacent boreholes.

 

[EireChch]

@Shubh_123 - Sounds reasonable.

And also like a job i would like to be involved in!!!

 

[oldestguy]

Assuming this is in a populated area the future may include buried utilities in the right of way. Thus, pile foundations or similar deep foundations will be the rule. Thus, If some unusual condition develops on the job, you can always bring in a drill rig and check it out. Thus, a boring at every pier is not justified for this situation..

 

[mikeofBelAir]

"Chop and wash" indeed. You may the "oldest guy"....but not by too much.

 

[dik]

Mike... OG is as old as dirt...

Dik

 

[oldestguy]

dik hit it right. Actually the handle came about when I joined and wanted to use "old guy". Someone already owned that one. So far havne't seen older competition and likely won't find them over 90. Hey friends I plan on at least ten more here.

 

[ukbridge]

From a lurker bridge engineer, who's at that age where you start to put on a bit of weight and lose a bit of hair, I've always enjoyed reading your posts oldestguy, dik, MadMike, fattdad et al.

heres to another twenty+ years, please keep posting!