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310 feet of 137.5 pcf soil embankment on precast concrete box culverts

310 feet of 137.5 pcf soil embankment on precast concrete box culverts

310 feet of 137.5 pcf soil embankment on precast concrete box culverts

FLAC uses model of the soil that uses a hyperbolic relationship between stress and strain for the soil. GEO5 currently only has the capability of an elastic – perfectly plastic soil (Mohr-Coulomb).The current report highlights as well as some of the literature highlights the limitations of the Mohr-Coulomb soil model. Furthermore, the Mohr-Coulomb soil as it is modelled in GEO5 creates instabilities in the model (the model fails to converge to a solution). I have been trying multiple scenarios (different meshes, soil properties, heights of soil layers) to get the models to converge to a solution but have been unsuccessful to get a full solution from a fully inelastic soil model. I do get a full solution from GEO5 when the soil directly surrounding the boxes is modelled elastically. Ultimately, this results in higher pressures than predicted by the FLAC analysis.

In the interim until I can get a fully inelastic soil model that I am comfortable with, I will run scenarios with the partially elastic model that I have currently working. Since the pressures are higher than those reported by the FLAC analysis, I consider the analysis to be conservative

RE: 310 feet of 137.5 pcf soil embankment on precast concrete box culverts

I'm unclear on the actual question. I am aware of this very project and look forward to your findings and the comments of others!

From my understandings, the hyperbolic model is to depict strain softening - i.e., modulus values decrease with confinement. Elastic materials do not behave like that - one modulus for all!

I am aware of conditions where the normal loads on such buried structures can actually exceed gamma*H. So, what do you mean by, "Higher Pressures?"

Good luck and wishes in your analyses. I'll wait for the book to come out!


ípapß gordo ainÆt no madre flaca!

RE: 310 feet of 137.5 pcf soil embankment on precast concrete box culverts

The pressures from GEO 5 FEM are higher than pressures from FLAC. These pressures from both programs that are higher than gamma*H are from shear forces from more settlement along exterior of culvert walls. See attached pdf?

RE: 310 feet of 137.5 pcf soil embankment on precast concrete box culverts

I'm still not sure of your question.

Yes, the pressure on an buried culvert can be higher than gamma * H.

Mike Lambert

RE: 310 feet of 137.5 pcf soil embankment on precast concrete box culverts

fattdad answered the why of GEO 5 being higher than FLAC. I was answering his question So, what do you mean by, "Higher Pressures?" Also, I was curious if anyone had similar results and work around with GEO 5?

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