lateral force design for a retaining wall. 2

[SNC STRUCTURAL]

Is there anyone consider a hydraulic force when design a retaining wall for general practice.

 

[msquared48]

Absolutely if the water table in the soil mass is higher than the base of the retaining wall.

Your Geotech should give you the lateral design values if the maximum height of the water table is known.

Mike McCann, PE, SE (WA, HI)

 

[SNC STRUCTURAL]

All of us know about it.
But there is a design in BC Evergreen line with over 9m tall retaining wall not designed with the subsoil water pressure.
Even they provide a subsoil drain on the wall, but the water penetration from top of wall and drain out from the subsoil drain will need a certain of time.
Due to BC in winter season will continue to rain for a month.
Usually, the wall will failure at the time when the backfill fill with water.

 

[jdonville]

If you know for a fact that the wall is deficient somehow, then you have a professional obligation to inform the relevant authorities to protect the safety and well-being of the public.

 

[r13]

Note that msquared48 is speaking the inclusion of the "ground water" in the analysis and design. What you mentioned is the surface water runoff, which is not considered as I am aware of. First of all, it is difficult to quantify the amount of runoff that is absorbed by/passed through the soil, secondly, there are batter ways to avoid damages/pressure increases due to seepage of rain water, than to punish the wall. However, shall problem arises, you shall follow jdonville's suggestion to ensure public safety.

 

[SNC STRUCTURAL]

Thanks for you suggestion.
I did raise up that issue to the BC engineer association but no one reply to me.
I create that talk is to proof as a citizen need to report something wrong and dangerous to life in the city.
But, it seems nobody care.
The issue is a retaining wall beside the Inlet Center station with 9.5m high.
This wall will affect the safe of the Evergreen line track, and CPR track just in font of the wall.
This project is design by SNC Vancouver structural team.

 

[oldestguy]

Your presumption of drainage came from what information? If you have some positive proof, maybe important, but nt personally showing standing water, etc. I'd also not get too excited abut your opinion. Unless compacted backfill, I'd not support your opinion.

 

[SNC STRUCTURAL]

Thanks for oldestguy.
I think you are knowledgeable enough to comment on the Geotechnical design.
The over all design for the stability is right on the Geotechnical point of view.
But, there are a lot of local design on the structural view.
The structural design involve reinforced concrete internal stress analyses.
It relate to loading obtained analyses and the wall self standing design.
The total lateral force by cases, to find out the worse case for the design and make sure it work under a certain case happening within a structural life.
This case is directly affect two transportation system, the Evergreen line and CPR rail both are standing side by side.
Under the life line consideration, the design is not safe during the sliding check only 1.29 on Static case and 0.99 on Seismic case exclude the water pressure.

 

[r13]

If the safety factors as stated, it is slightly fall short of normally desirable, but not by a mile. Is anywhere shown soil corrosion, or localized slop failure, ponding..? Take photos, best in a stormy day, as the runoff is most severe.

 

[BridgeSmith]

the design is not safe during the sliding check only 1.29 on Static case and 0.99 on Seismic case exclude the water pressure.

It'd debatable whether combining the water load with seismic in this situation is warranted, given the tiny statistical probability of major rain event and a seismic event occurring at the same time. The consequences of the 'failure' also should be considered. If the wall slides a few inches in the unlikely event of the design magnitude earthquake, would it be catastrophic(i.e. would lives be in immediate danger)?

We allow for all sorts of things to be damaged or fail during an earthquake, so long as it repairable and doesn't endanger human life. It's written into the AASHTO bridge design code - the criteria for most of our seismic design is "life safety".

Rod Smith, P.E., The artist formerly known as HotRod10

 

[SNC STRUCTURAL]

Thanks, BridgeSmith,
The Civil work design always need to concern about public safety and against the worst case.
There are many cases of safety for the design, if for a life line design anytime the structure should be functionally work.
Can you think about a train running and the track off set a little bit? How many life will be injure?
Is there somewhere I can report to?

 

[BridgeSmith]

If you can have a conversation with the engineer who designed the wall, I would start there. If you have the opportunity for that, be respectful and open to the possibility (I daresay probability) that your information about the design is incomplete, and the guy who put his stamp on the design, taking the responsibility for its adequacy and safety, did actually know what he was doing, and you don't. Forgive me for being blunt, but questioning another engineer's design is not something to do lightly or flippantly. If there are site considerations he wasn't aware of, I'm sure he'd want to know.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[SNC STRUCTURAL]

Yes, total agreed.
I have been working in the industry for 50 years. I wouldn't easy comment on other's design until I found something danger to public.
I did go through the Geotechnical report and the design brief there are some grey area.
But, my question is very straight forward against the local failure on sliding because it is a self standing cantilever retaining wall.
Public safety always be consider the first!!

 

[BridgeSmith]

Can you think about a train running and the track off set a little bit? How many life will be injure?

Depends on the typical speed of the train and whether there happens to be one at that particular place at the moment that the earthquake hits.

"I have been working in the industry for 50 years."

And you've been an engineer for the all that time?

"I wouldn't easy comment on other's design until I found something danger to public."

There's many potential dangers to the public, some more likely than others. There are not unlimited funds to address every potential danger, regardless of the likelihood of occurrence. Being theoretically within 1% of the wall not even moving during the design earthquake may have been deemed an acceptable risk. There's also the possibility that the engineer used a different method to calculate the seismic loading. Seismic design is constantly changing as new data and experience refines, and sometimes revolutionizes, how we quantify the effects of earthquakes. Are you sure your analysis incorporates the most up to date understanding of seismic load effects on retaining walls?

I just want you to be sure that you know what you think you know, because making those kind of accusations without a solid foundation can get you into a world of trouble.



Rod Smith, P.E., The artist formerly known as HotRod10

 

[r13]

"working in the industry for 50 years" does not make your ungrounded question on an existing design reasonable, nor the lacking evidence threat claims of "public safety" would. Please bring in some measurable evidence of potential failure, otherwise there is no legit reason for concerns.

 

[miningman]

Gotta say it. The OP appears to be an employee of SNC Lavalin , whom he claims was responsible for the design of this structure. Fromm these posts, it appears that English is not the OP's first language and yet he claims to have 50 years experience...... that puts him at over 70 years old. I wouldnt say something doesnt add up here,, Id say theres a whole pile of stuff that doesn't add up!!!.

 

[BridgeSmith]

The OP appears to be an employee of SNC Lavalin, whom he claims was responsible for the design of this structure.

Good catch! I didn't notice the "SNC" in the OP's handle and the design group before, but now that you brought it to my attention, I noticed that the OP is in British Columbia, and the OP said the design was "by SNC Vancouver structural team". So, it would seem the OP not only works (or worked?) for the company that designed the wall, but presumably in the same office. I looked a little more, and I see 19 offices in BC, so maybe not the same office. Still, a "structural" working for the same company, in the same province, should be able to easily contact a member of the design team directly with any concerns.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[SNC STRUCTURAL]

Thanks for everyone's comments.
There is a very important basic concept soil and water always be the first consideration for a retaining wall design.
Most of the failure of a retaining wall is the soil contain high volume of water.
You can find those retaining wall beside the a rail track that create a concern of safety to the public.
This case I saw the geotechnical report denoted a subsoil drain needed for the wall.
That means water is a concern in the design.

 

[BridgeSmith]

Again, I suggest you discuss your concerns with the design engineer.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[phamENG]

but the water penetration from top of wall and drain out from the subsoil drain will need a certain of time.

This is the crux of it, isn't it? Did you happen to do an analysis of the drainage system to determine how much water can be retained? It's not a question of time, really - it's a question of static head required to produce maximum flow through the drainage system. Until you calculate that, I would say it is inappropriate to formally accuse somebody of an unsafe design. If you have, and determined that even at max flow the drainage layer will still have 3m of water and the wall was designed for no water, then you should absolutely bring it up. But if you don't have that number and you're just going on a hunch that it wasn't properly accounted for, you're setting yourself up for professional embarrassment (at best) or possible legal action if you're proven wrong.

As for seismic - I completely agree with BridgeSmith. The odds of a design rain event occuring during seasonal high ground water just before a design earthquake are laughably small. On top of that, a train would have to be running on or within stopping distance of that point to be negatively impacted. The odds of that happening are about as good as everyone on the train buying the same winning lotto ticket numbers AND being struck by lighting. It's simply out of the realm of reasonable design conditions. If there is a significant earthquake, trains won't be running. They'll have to inspect the track for damage first. The odds of the train itself being toppled over in a design event is probably higher than the wall moving an unacceptable distance.