Laws behavior

[killswitchengage]

Hello,
I've been thinking about it , where i studied we were fed all the time the notion that Mohr Coulomb criterion is reliable in soil mechanics" all the time" . But after seeing the vast number of laws that exists out there , for instance visco elastic or visco elasto plastic behavior which are never used by engineers , let alone know there existence ! i am starting to believe that engineers should not stick to long held notions or beliefs and rely on their instincts . If i feel that a particular criterion is useless or unreliable , i should use another one.

Finally what do you guys think about it ? what do you use ?

 

[Ron]

It's called "engineering judgment".

 

[Retrograde]

I agree with Ron. Depending on the situation you may want to consider more advanced models such as the Hardening Soil Model or the Hoek-Brown model.

 

[killswitchengage]

can someone provide an example he faced ?

 

[Retrograde]

A project I am currently working on the piling contractor used the Hardening Soil model with small strain stiffness in Plaxis for the contig pile wall design.

 

[SlideRuleEra]

I am starting to believe that engineers should not stick to long held notions or beliefs and rely on their instincts...can someone provide an example

Driving timber piling to obtain point bearing in soil with thin layers of limestone marl. Pile penetration slows when a layer is reached. If a few more hammer strikes are allowed to formally determine the blow count, either the pile point brooms or the pile punches through the layer and starts moving again. Best to go with real-time observation, intuition and experience to terminate driving after one or two low-penetration hammer blows. If the pile driving is being performed with a typical single-acting hammer operating at approximately 60 blows / minute, that allows about 2 seconds to make a decision.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[killswitchengage]

interesting
i have another example , if you are facing a highly sensitive soil best stick with a thixotropic model behavior for the mud rather than the typical Mohr Coulomb especially when we are talking about mudslide for instance.
Another example relates to geosythetics and their creep behavior or relaxation

 

[Ron]

SRE....good example. Also in some of our marls to the south of you, the remolded strength after driving is significantly greater than the blow counts would support during initial driving. Let the pile sit for a couple of days then go back and re-tap.....the blow counts go up tremendously.