Heave and shear 2

[btomcik]

In designing temporary / short-term sheet pile wall and soldier pile wall earth retention systems, have you in your experience checked for system stability such as heave?

Also, is shear commonly checked when designing said earth retention systems?

Please share your experiences.

 

[escrowe]

Heave of the excavation bottom is significant
with very loose and/or permeable soils,
and when working below groundwater.
To check for heave or a quick condition, you must
determine the permeability of the soils
and the elevation of groundwater.

Retaining systems are essentially designed to resist shearing forces, including loads from saturated soils
and swelling clays. The piles will certainly be subject
to unbalanced lateral loads.

Your geotech should help you address these concerns.

 

[btomcik]

What methods or procedures are there to check stability of an earth retention system? I'm talking about temporary sheet pile and soldier pile systems.

 

[escrowe]

The first step is gathering subsurface data
related to groundwater location and soil strength.
Think SPT or CPT borings.
That data can be modeled to design and/or
check the stability of the retaining system;
programs like LPILE and CWALSHT are sometimes used to
confirm the size and embedment of the members
and to calculate soil-pile interaction.

Individual piles can also be subject to lateral load tests,
which are handled by the contractor and geotech test company.

---

How temporary is temporary? More importantly, what size is the excavation?
If the project only calls for shoring a utility trench excavation (for example)
it might be better to consult with the utility contractor
or contact an experienced shoring contractor:
there are temporary, portable, hydraulic shoring systems that
are suitable for trench support, which are primarily limited
by depth and width of the trench.
I've seen portable integrated systems
that can handle 25-foot deep excavations.

 

[PEinc]

btomcik,

No offense intended but you should read some of the references you requested in other threads before asking all of these questions. Please don't ask questions as a substitute to first doing your homework.

 

[btomcik]

Not much offends me. But the holier-than-thou attitude that some people exhibit in these forums is uncalled for. It's a help forum, and nothing more. Yes, people should do research first, but when they already have, there is no reason they should be told their questions are too basic or simple or they need to do more homework.

I've read a ton of references and am asking a lot of questions because the references are unclear and I don't have an engineering mentor or consultant I know of that I can ask questions to.

Here is a list of references I've read and re-read:
Principles of Foundation Engineering, Braja Das
USS Steel Sheet Piling Design Manual
Design of Sheet Pile Walls, US Army
Trenching and Shoring Manual, CalTrans
Civil Engineering Reference Manual
(next on my list - Sheet Pile Design, Pile Buck)

Where am I going wrong? I apologize if my questions are too basic or simple.

Thank you to those of you who have responded to my posts and have taken the time to answer my questions. Your insight and input has been incredibly valuable especially as I start again in the field of design.

 

[PEinc]

As I said before, no offense intended; no apology needed. I never said your questions were too basic or simple. To the contrary. Some are probably too complicated to discuss in a forum. The references cover the topics better than you can get in a forum. When you ask if certain things need to be checked, the answer is yes. However, you will find that some, such as soldier beam or sheet pile shear and heave, are usually not a concern if you have relatively normal soils. Until you have done a few designs and built the walls, you may not have a feel for what is needed. What you have to check (not what you need to check) sometimes depends on who is reviewing and approving your design. Some engineers and agencies obsess over designing some things that really don't often need to be designed (such as temporary lagging boards and soldier beam web crippling). The more references you read, the more conflicting information you will find. Some references are heavy on theory but light on common sense and real world experience.

 

[escrowe]

I try to remember that almost every project has been done before, and lessons have been learned.
In our wonderful age of the internet, a lot of this wisdom is available on line.

So rather than agonize over the perfect design procedure, I focus on gathering the existing wisdom.
This is a good place to start, and I've found that providing more project-specific information often generates more useful and insightful answers.

 

[btomcik]

escrowe:

Thanks for your posts in this thread. For me at this point, I’m not concerned with a perfect design procedure and I don’t have a specific project yet to ask specific questions on. Each project is different and no specific or perfect design procedure will fit each case anyway.

I’m getting reacquainted with earth retention design after many years away from it. As mentioned in my last post, I’ve read a ton of references trying to get back into the swing of things. I ask a lot of questions because as a professional engineer, I don’t believe in blindly accepting the mathematics or something just because it’s printed in a book. I want to understand why something is so I can use that knowledge to make an appropriate engineering decision on a project in the future. Some of the information is unclear or conflicting between references, and since I don’t have a mentor or consultant I know of to ask questions to, this forum in the only place I can go.

Maybe for some who have decades of experience in this field, my questions are stupid, a waste of time, something I should already know, or common knowledge. Well for me they’re not, or I wouldn’t be asking them. Coming to a help forum, people expect to get help, not chastised. Sometimes people need to be reminded of that.

In the future I will try to be as specific as possible with my questions. Thank you again for your help.

 

[DRC1]

Don't feel bad. Not a lot of people really understand how to do shoring. The references you have listed are good, except I am not really familiar with Das. If you are getting Pile Buck, get the new Pile Buck. The Old one is very similar to The US Steel Book. One other reference is Bowels Foundation Design and Analysis. Although I don't agree with everything he does, he does a pretty good job of explaining how to design things both geotechnically and structurally.
I statred with the old Pile Buck ,which is very similar to the USSheetpile Manual. I read the thing studied the problems, then went back and tried to solve the sample problems myself. Then I worked My way through the poblems in Bowles. There is no quick course and there are not a lot of people who really understand it. Sheeting design, for many reasons is somewhat different than geotechnical engineering.
To answer your question - yes I have checked for heave or piping. Heave occurs in cohesive materials. Piping or quck condition occurs in sands blow water table. US Steel Details how to do both of these post back if you have questions. Heave occurs if the clay is too soft for the excavated face and is similar to a bearing failure. Deep excavations in soft clay can be tricky.
Piping occurs when the water flowing into the excavation has sufficent upward force to reduce the effecive stress of the sand. Typically if you can control the excavation with pumping, piping is generally not (but not allways) a problem. Due to the permiable nature of soldier pile & lagging, they are generally not used in situations where piping may be an issue.
The best thing to do is a) don't worry about having the perfect design. Start by being fairly conservative and as you get more of these designs under your belt, you will be more comfortable with what you can do.
B) get out in the field to see how it is being built. Construction engineering is very interactive and there will be a lot of feedback from the field.
Good Luck and keep posting.

 

[PEinc]

B) get out in the field to see how it is being built. Construction engineering is very interactive and there will be a lot of feedback from the field.

Excellent advice, DRC1. Most field crews know so much more about what wall members are needed than does the engineer designer. If you don't believe me, just ask the field crew. You need to keep both eyes on them, even the better crews.