Hand Probe
Hand Probe
(OP)
Is using a hand probe a good method to determine foundation bearing capacity? For MSE wall foundation, what would you recommend to be used to check/calculate bearing capacity?
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RE: Hand Probe
Not trying to be difficult, however. . .
f-d
¡papá gordo ain't no madre flaca!
RE: Hand Probe
probing essentially checks the surficial consistency. in my opinion, the probe rod is probably the best tool we can carry with us. we also perform hand auger borings with dcp during construction and soil test borings during the exploration phase. the wall designer should specify the testing criteria so that the geotech "understands" what is expected.
on another note, the wall designers (at least some) attempt to throw the stability analysis back on the geotech. i still maintain "what the heck are they designing if they use a cookbook approach selling the same design year after year and don't actually do any engineering to design the wall for the site soils instead of simply providing a wall design with the expectation that the owner or owner's rep is responsible for making the onsite soils satisfy the design". simply put, the wall designer should be responsible for contracting the geotech for these things so that the owner is not stuck taking the liability. then, if the designer's geotech wants to do all the design work with no fees, that's between the designer and geotech.
ok, i've worked in my soapbox speech so i'll not beat it to death.
RE: Hand Probe
Kinda seat of the pants engineering, but it works for me.
Mike McCann
MMC Engineering
RE: Hand Probe
RE: Hand Probe
RE: Hand Probe
Then, using the rod probe technique, related to what you have experienced when you run field density tests and look for some degree of percentage of compaction on production of compacted fill, chances are you will find that probe is not too bad for a general idea of relative density or percentage compaction, etc.
On the thought as to where you may stand in court using this as an "engineer's tool", tied in with your years of experience, it would be difficult for someone to argue that I don't know what I am talking about using this method, when you look at the hundreds of cases where I've used it with no failures to make quick evaluations of soil conditions, followed by more sophisticated testing to back it up. It is a step above an umbrella that once was common.
RE: Hand Probe
Still, we had a few failures of a 9m high wall sitting on Su = 20kPa clay some 6m thick. Rightly, this embankment fill (made of the RE Wall) might technically be called a slope stability problem/failure (using Bishop or other methods of analysis) clearly the 10m x 20 kN/m3 = 200kPa > 6 x 20kPa (ultimate bearing - approx) - and the wall did a tumbling in rotation - like the bearing capacity problem in Lambe and Whitman (Chapter 32 on Shallow Foundations with Undrained Conditions (Fig 32.1).
RE: Hand Probe
don't construe my somewhat negative comments about mse walls or their designers as opposing the use of the things. i think they are an excellent choice in some situations. however, some (not all) of the designers here (which apparently is not the "norm" elsewhere) choose to take a contractual approach that transfers their liability to everyone else involved...but owners and even some geotechs unknowingly accept it because they don't see the potential implications. the more and more geotechs i've seen that get bit by lawsuits for these things, the more and more they reject the ridiculous language and assumptions put out there by the designers.
RE: Hand Probe
My company started out providing geotechnical parameters for MSE walls, then evolved to providing plans, then just said to heck with it and started building the darned things.
I once saw an MSE wall failure attributed to tree growth at the top of the wall. We estimated a surcharge of about 75 tons of vegetative matter.
RE: Hand Probe
Personally, I would not utilize a probe rod only to determine bearing capacity. I have used the probe rod in the field during site grading and construction, with experience and supplemental subsurface testing (hand auger borings, test pits, additional soil test borings, etc.) to complement the original geotechnical investigation.
Personally, most MSE wall plans I have seen do stipulate a bearing capacity. Now, when checking the bearing capacity using the traditional formulas, I use the reinforced length as the foundation width.