correlation between modulus of subgrade and pmt test

[killswitchengage]

Hello

Are there any correlations between Menard test and Ks modulus of subgrade by any chance ?

thank you

 

[SoilRocks]

I assume you are referring to a pressuremeter test. You probably could get some elastic properties from a test (initial loading) in homogenous materials at a similar depth (I assume near surface). This would only be relevant for very shallow influence loads in unsaturated soils. For instance, if you were trying to figure out the k value under a slab for forklift or rack loading, etc. It would not be very appropriate for footings or mats with much deeper zones of influence, consolidation of saturated clays, etc. Remember, modulus of soil subgrade values are not soil properties - they are model elements just representative of the load-deformation response of a defined loading condition.

Hope this helps.

 

[Okiryu]

Perhaps you can get the elastic modulus from the PMT and then calculate the Ks using Ks= Es / B* (1-v^2) in F/L^3 units. See Bowles book equation 9-6a.

 

[killswitchengage]

Thank you both and sorry SoilRocks for being late . Yes we are having a bit of an issue conducting plate load test in a quay in order to design slabs for forklift and rack loading vehicles , however the soil is actually a fill up to maybe 9 m. About the modulus of subgrade do you mean that it might change from one point to another ?

Okiryu thanks a lot this can could be handy .

 

[GeoEnvGuy]

I am not a supporter of determining settlement through the modulus of subgrade reaction, I know the structural engineers like the theory so I ask them what they want to use for the foundations or piles youngs modulus and moment of inertia or foundation stiffness.

Okiryu has provided a simplification of the original Vesic interpretation presented in Bowles. The full formula is provided in the image below where Bowles simplifies a twelfth root and 0.65 to be equivalent to 1.

 

[SoilRocks]

Killswitchengage - You are fine just using assumed properties for industrial floor design for forklift and rack loads, or better yet, get a sample of the import fill, and run a CBR or R-value and correlate to subgrade modulus. Multiple PCC and other correlations have good correlations for the analysis you are looking at (because it is shallow zone of influence, and unsaturated). You can also typically increase the modulus somewhat by including a good quality baserock layer underneath the slab as an underlayment. Of course, a plate load test on the finished subgrade would be really cool to get and high quality, but not always possible. There are references out there for industrial floor design for just this design process. As I mentioned before, this would not be useful at all for foundation design - this is just for industrial floors. Let me know if you need more input. Cheers!!

 

[killswitchengage]

I am not sure if i understand you guys , but i am trying to use Westergaard method for rigid pavement design . Thing is , since the quay is fully operational demolishing the already existent slabs and reaching out for the sub grade is kinda tricky , not to mention that papers authorizations can be a pain and since PMT tests were conducted so i was curious about that , i mean the two tests are kinda similar to a certain extent at least for the pseudo elastic region .

One thing is for sure the subgrade will be replaced by a better suited compacted material maybe a unbound gravel 0/40 mm ( i am using imperial units here ) so maybe a young modulus of 400 MPa is possible , and like SoilRocks said plate load test will be carried out as the project progresses to confirm these values.