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Vertical/Hori Subgrade Reaction for single pile 1
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so much.First subgrade modulus is not a soil property. Structural engineers need to stop using this for foundation design.
Second, the property you need and should want is Young's Modulus obtained at an appropriate shear strain level. If you are interested in settlement, then that rules out use of "E" estimated by SPT (never should any geotechnical engineer use blow counts to get N, even in sand) and it also rules out CPT
"estimates" because both CPT and SPT completely destroy soil structure and stress history because they shear at strain levels from 10 to over 100 percent. See attached figure.
Third, you need to rely on an in-situ test that tests the soil at an appropriate shear strain for the intended application. For consideration of settlement, typically suitable shear strains are in the range of 0.0001 to 0.001; in this range, both Pressuremeter and flat blade dilatometer testing can be useful. Pressuremeter is good for clays sufficiently stiff to remain open through medium strength rocks. By contrast, the DMT is very appropriate for all sands, cohesive soils, through to soft rock with up to 400 MPa. The lateral Young's modulus is readily obtained from both of these tests.
Second, the property you need and should want is Young's Modulus obtained at an appropriate shear strain level. If you are interested in settlement, then that rules out use of "E" estimated by SPT (never should any geotechnical engineer use blow counts to get N, even in sand) and it also rules out CPT
"estimates" because both CPT and SPT completely destroy soil structure and stress history because they shear at strain levels from 10 to over 100 percent. See attached figure.
Third, you need to rely on an in-situ test that tests the soil at an appropriate shear strain for the intended application. For consideration of settlement, typically suitable shear strains are in the range of 0.0001 to 0.001; in this range, both Pressuremeter and flat blade dilatometer testing can be useful. Pressuremeter is good for clays sufficiently stiff to remain open through medium strength rocks. By contrast, the DMT is very appropriate for all sands, cohesive soils, through to soft rock with up to 400 MPa. The lateral Young's modulus is readily obtained from both of these tests.
Eg1776 - interesting perspective. It sounds all well and good to tell everyone to use DMT or pressuremeter test to determine Young's Modulus (E') however in the real world I think a lot of engineers do use a correlation between N and E'. I have correlations in NZ and it is widely used in the UK too. CIRIA Report 143 'The standard penetration test (SPT): methods and use' gives the correlation of E' = N (MPa). (i.e. for an N of 10, E' would be 10MPa. For cohesive soils E' = 0.9N (MPa). It also gives a correlation for E' from Undrained Shear Strength of E' = 130 x Cu (kPa). I am not saying this is correct and you are wrong, just my two cents.
For most site investigations a boreholes with SPTs are prescribed. U100s would also be prescribed to get undisturbed samples for triaxial or Odeometer tests. DMTs and Pressuremeters are somewhat rare.
Would pressuremeter and DMTs be the 'norm' for testing in you area?
PS - sorry to high jack the thread but couldnt help comment.
For most site investigations a boreholes with SPTs are prescribed. U100s would also be prescribed to get undisturbed samples for triaxial or Odeometer tests. DMTs and Pressuremeters are somewhat rare.
Would pressuremeter and DMTs be the 'norm' for testing in you area?
PS - sorry to high jack the thread but couldnt help comment.
eg1776, nice graph. My experience is that typically, the modulus from the pressuremeter tests is much larger than the unconfined compressive strength tests. As you mentioned, this is based on the strain ranges which is different for both tests.
Ok, are you an engineer dedicated to quality? If you are, you would be like any physician fighting for the life of your patient using the Best treatments and technology available. If not, then you are lazy and ignorant of the importance of continual improvement and innovation and should not call yourselves a professional. Come on, the SPT has not change in any significant way since BEFORE the Wright brothers flew at kitty hawk NC. And if someone prescribes use of SPT, it is your duty as a professional to educate your client and tell them what is needed. If you cannot do that, you should stop calling yourself a professional.
This is not going well. . .
Firstly, the modulus of subgrade reaction [f/l^3] is not the same thing as the soil modulus [f/l^2].
Secondly, the OP never stated the end game. Just because we can tell you something doesn't mean we don't want to know what you are going to do with the answer. I can't think of one good reason why we'd need a vertical modulus of subgrade reaction in designing a single pile. I can think of a reason to get the horizontal modulus of subgrade reaction - i.e., like to look at P-Y relations?
I think the ENRIRE geotechnical profession understands the limitations of the SPT. To cite such limitations in a disparaging tone, is too aggressive for me!
I think we also understand the successes and limitations of the CPT and the DMT. I mean these have been in use for over 30 years.
I am also a fan of the DMT. That said, I oversee many projects where all we end up with is N-value. With some responsible charge over the geotechnical matters of the third largest DOT in the United States, we still have projects with various data gaps. Heck, I can't oversee them all!
I can certainly tell though when it's a case suited for N-value interpretation and when it's a project that needs the extra mile. I would never extrapolate somebody using N-value on a project is being negligent.
So, to the OP, what's the end game?
f-d
ípapß gordo ainÆt no madre flaca!
Firstly, the modulus of subgrade reaction [f/l^3] is not the same thing as the soil modulus [f/l^2].
Secondly, the OP never stated the end game. Just because we can tell you something doesn't mean we don't want to know what you are going to do with the answer. I can't think of one good reason why we'd need a vertical modulus of subgrade reaction in designing a single pile. I can think of a reason to get the horizontal modulus of subgrade reaction - i.e., like to look at P-Y relations?
I think the ENRIRE geotechnical profession understands the limitations of the SPT. To cite such limitations in a disparaging tone, is too aggressive for me!
I think we also understand the successes and limitations of the CPT and the DMT. I mean these have been in use for over 30 years.
I am also a fan of the DMT. That said, I oversee many projects where all we end up with is N-value. With some responsible charge over the geotechnical matters of the third largest DOT in the United States, we still have projects with various data gaps. Heck, I can't oversee them all!
I can certainly tell though when it's a case suited for N-value interpretation and when it's a project that needs the extra mile. I would never extrapolate somebody using N-value on a project is being negligent.
So, to the OP, what's the end game?
f-d
ípapß gordo ainÆt no madre flaca!
Lazy, ignorant and unprofessional.....charming. Good thing i am thick skinned.
The reason the SPT has been around since before the Wright brothers is because i has stood the test of time. Is it crude?, yes, is fast, cheap and readily available?, also yes.
As stated already, it comes down to knowing the limitations the risk associated with using and SPT when another testing method may be more appropriate. I would guess that far more structures etc have been designed based on SPTs than DMTs....they appear to be doing ok.
The reason the SPT has been around since before the Wright brothers is because i has stood the test of time. Is it crude?, yes, is fast, cheap and readily available?, also yes.
As stated already, it comes down to knowing the limitations the risk associated with using and SPT when another testing method may be more appropriate. I would guess that far more structures etc have been designed based on SPTs than DMTs....they appear to be doing ok.
p.s., for compacted soils, you can obtain correlation between CBR and the modulus of subgrade reaction. Refer to DM 7 (if you can find it).
p.p.s., in today's MEPDG pavement design, derivation of resilient modulus is quite complicated. So complicated, in fact that most of the DOTs are correlating to UCS (fine grained) or AASHTO soil type (coarse grained).
f-d
ípapß gordo ainÆt no madre flaca!
p.p.s., in today's MEPDG pavement design, derivation of resilient modulus is quite complicated. So complicated, in fact that most of the DOTs are correlating to UCS (fine grained) or AASHTO soil type (coarse grained).
f-d
ípapß gordo ainÆt no madre flaca!
SPT's provide excellent correlation for a number of material parameters in situations where the properties of the prevailing soil have been documented exhaustively, or even somewhat so. We use N-values in design work all the time...if anything fishy arises we can pick it up immediately, because we know exactly what we're dealing with.
Good thing we're all thick skinned...vociferous rants don't go hand in hand with good engineering.
The O.P is unusual- as fattdad has suggested- the subgrade reaction modulus could be gauged relative to the material CBR. If however you insist on having accuracy for the in-situ material, relatively expensive testing would need to be sought. I wouldn't pursue that without first consulting a local geotech...it's highly unusual to require precision in the application you've described.
All the best,
Mike
Good thing we're all thick skinned...vociferous rants don't go hand in hand with good engineering.
The O.P is unusual- as fattdad has suggested- the subgrade reaction modulus could be gauged relative to the material CBR. If however you insist on having accuracy for the in-situ material, relatively expensive testing would need to be sought. I wouldn't pursue that without first consulting a local geotech...it's highly unusual to require precision in the application you've described.
All the best,
Mike
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