bridge abutment settlement 1

[ac4u2nv]

Dear all
Im looking at a bridge which has suffered from settlement since construciton 20 years ago. It is beleived the abutments were built on mass concrete fondations on Weald Clay, and this clay wasnt allowed to presoncolidate fully due to time constraints.

How do it test the clay beneath the abutment foundations? I was planning on comapring that with another neary by borheoles result to see how much the it could theoritically consoliate and how much much consoldaition has taken place already (beneath the abutmenet) and how much more can be expected.

Please advise.

Thank you

 

[fattdad]

don't rule out secondary compression. In otherwords, make sure the time readings extend sufficiently beyond the end of primary to get a good value of C-sub-alpha. If the stress history in the formation was originally the same, you'll then see both the influence of the abutment on strength, Pp and C-sub-alpha.

f-d

ípapß gordo ainÆt no madre flaca!

 

[oldestguy]

Adjacent sampling should be oK. However, are you sure there also isn't some displacement of support soil perhaps due to erosion by flowing water?

 

[Okiryu]

I am working in a similar project now- investigate current settlements of a warehouse slab due to consolidation settlement. But since the structure was constructed 20+ years ago, I am considering secondary compression as fattdad mentioned.

 

[msquared48]

Impact? Vibrational settlement?

Mike McCann, PE, SE (WA, HI)

 

[HENRYZAU]

Borehole is a rather crude method for soft clay, I would go CPTu or DMT thru the embankment (predrilling may be required) and in virgin ground nearby (not affected by the embankment load), then compare the yield stress of the soft clay before and after the embankment and work out how much primary to go and how much creep (secondary) to go in its design life.

 

[ac4u2nv]

fatdad - i have no hisotirlca data on the ground or testing prior to or during construction. how would i be able to compare if i dont have any stress hisotry?

 

[r13]

Outside of the backfill zone, the soil should be quite representative of state of pre-construction condition.

 

[ac4u2nv]

how do i compare the preconstruction soil to that which is below the abutments foudnation without being able to sample that area?

 

[r13]

I would like to think there is method for coring as the abutment is an isolated structure rather than clustered footings. You might have to asking around.

 

[fattdad]

To my question: Drill a few hundred feet away from the bridge in a natural setting. Then also drill into the same formation at the bridge site. Run a lab program and compare the results.

f-d

ípapß gordo ainÆt no madre flaca!

 

[geotechengineer1]

To determine where you can drill, think about the zone of influence of your foundation (using a 2V:1H load distribution or whatever you prefered method is). You should find that it is not absolutely necessary to drill through the abutment itself.

Some testing ideas:

CPT's, particularly with dissipation testing can be quite useful.

Cored boreholes with slug testing

Cored boreholes with frequent push tube samples to run 1-D consolidation tests on.

That being said, you really need advice from a senior / principal geotechnical engineer at your firm for a job like this.