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

[edward1]

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

 

[fattdad]

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!

f-d



ípapß gordo ainÆt no madre flaca!

 

[edward1]

fattdad,
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?
edward1

 

[GeoPaveTraffic]

I'm still not sure of your question.

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

Mike Lambert

 

[edward1]

Mike,
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?
Thanks,
edward1