RC Retaining Wall - concrete additives required?

[kellez]

Hello everyone, I am designing a 3.5m high retaining wall of which 2.0m will be covered by infill soil. see picture attached

I have specified a layer of bitumen felt to be applied on the wall up to 2.2m high.
Next on top of the bitumen felt i have specified the installation of a geodrain membrane.

Do you guys think i will also need to specify additives to the concrete such as crystalline waterproofing?

Regards

 

[XR250]

I would also show a foundation drain and backfill with a freely draining material. I never specify waterproofing systems on retaining or masonry walls. There is too much liability and it is just another thing i have to stay on top of for new developments. I put a note "waterproofing by contractor as required"

 

[MotorCity]

Why do you want to waterproof a retaining wall? Typically we only waterproof occupied or liquid retaining structures. Drainage mitigation behind the wall is a good idea but that is different than waterproofing. You will also need a drain running along the bottom of the wall and/or weep holes through the wall. You need to provide a path for the water to go once it reaches the bottom of the wall.

 

[dik]

For a 200 wall, do you need two layers of rebar? and you should batter the wall into the soil by 70 to 100mm... so, when it rotates, it becomes more vertical. Also free draining back fill and drains at 1200 with rodent screens.

Dik

 

[WARose]

I don't think I've ever specified waterproofing for a soil retaining wall.

By the way, why no toe on the wall footing? Are you near a property line?

 

[dik]

WARose... same here, just clean free draining backfill, filter cloth and drains...

Dik

 

[WARose]

WARose... same here, just clean free draining backfill, filter cloth and drains...

And you can count on those drains getting clogged eventually.......ergo I always check it with the (additional) hydrostatic pressure. (If applicable.)

 

[dik]

Never had that problem... the geotextile between the clean stone and existing soil keeps the clean stone, 'clean'.

Dik

 

[WARose]

Never had that problem... the geotextile between the clean stone and existing soil keeps the clean stone, 'clean'.

Most of the time my backfills are not that neat/organized.

Anytime they have been....the contractor gripes to the owner, and then I hear about it.

 

[dik]

I insist... and have standard details that are included in the contract documents. I ask the contractor what sort of credit he is prepared to offer... I then explain to the owner about the long term viability of his wall and the redesign and the added loading for hydrostatic surcharge. Never been an issue.

Dik

 

[kellez]

Hello everyone,

The only reason I wanted to provide waterproofing to the retaining wall is because I have seen crystalline waterproofing being used on slab foundations for residential houses here in my country,
therefore i was just wondering if they also use it on retaining walls since they are mostly in contact with soil.

Thank you everyone for your advise, I will make sure to add the detailing for the backfill with a freely draining material and also add a drain pipe at the bottom of the wall, however where is that drain pipe supposed to take the water to? Also how am i supposed to provide an inclination to the drain pipe?

By the way, why no toe on the wall footing? Are you near a property line?

You are right i am exactly on the boundary of a plot which needs to be filled with soil to increase the level height in order to reach the level of the road

For a 200 wall, do you need two layers of rebar? and you should batter the wall into the soil by 70 to 100mm... so, when it rotates, it becomes more vertical. Also free draining back fill and drains at 1200 with rodent screens.

According to my calculations no actually i do not need two layers of bars, but i am being carried away by other engineers designs here in my country, which makes me feel a bit worried to go along and use only one layer while an experienced engineer uses two layers

What exactly do you mean by "batter the wall into the soil by 70 to 100mm"

The drains at 1200 with rodent screens you mention are called weep holes?



Anyone have a picture of the drain pipe with geotextile used on a retaining wall?

 

[kellez]

Any idea where I should drain the water to from the bottom of the retaining wall? Please have a look at the pictures below ti get an idea of the site layout


Blue colour in the plan view below is the retaining wall

https://res.cloudinary.com/engineering-com/image/upload/v1512033297/tips/Screen_Shot_2017-11-30_at_09.59.14_ahrtko.png
[img [URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1512050295/tips/Screen_Shot_2017-11-30_at_15.57.39_uz2i45.png[/URL]

 

[dik]

Unless your concrete placement is really good... I'd not use 2 layers of bars in a 200 wall... 250 wall minimum for 2 layers. You're looking for segregation issues.

I'll see if I can readily locate a wall section.

Dik

 

[kellez]

Unless your concrete placement is really good... I'd not use 2 layers of bars in a 200 wall... 250 wall minimum for 2 layers. You're looking for segregation issues.

I'll see if I can readily locate a wall section.

Thanks for the advise, actually i have seen quite a few 200mm thick being build and poured just fine however the bars of each layer are alternating, what i mean is that one layer is shifted by a distance = half the spacing of the bars therefore the bars of each layer are not exactly on the same axis. see picture for clarification.

However another important reason to use only one layer is the cost savings


so from the top view of the wall it would look like this

 

[JoelTXCive]

Currently you have a cantilevered wall with no toe due to property line issues. I am concerned that your heel reinforcement bars will not be fully developed since you only have the stem to work with. Have you considered battering the rear side of the wall. A battered wall is thicker at the base, which will push your heel's flexure critical section rearwards. That will give you more room to develop the steel in the heel.

Below is an excerpt from ACI's Concrete Design Handbook showing the critical section for the heel. The CRSI Retaining wall design guide has a similar discussion about development length of heel bars.

 

[JoelTXCive]

 

[dik]

kellez: You shouldn't stagger the vertical reinforcement. If same spacing, then the bars should be opposite each other. I should have added that it's the horizontal reinforcing that causes the segregation...

Dik

 

[msquared48]

What about sliding resistance and frost depth considerations?

Mike McCann, PE, SE (WA)

 

[msquared48]

Where in Greece is the project?

Mike McCann, PE, SE (WA)

 

[SlideRuleEra]

Kellez - For a "thin" (200 mm) wall, have the Contractor construct short lengths of the wall. Whether there is one rebar mat or two, there is no room to get a tremie pipe or concrete pump hose to get inside the forms. Agree with Dik about segregation and there is an additional concern:

As the concrete works it's way down inside the forms, it coats the rebar with concrete residue. If the wall is placed quickly (a short length of wall) this is not a problem. If a long length of wall is constructed, it may take too much time to fill the forms. The residue on the upper rebar may have "set" before it is covered... affecting the bond strength.

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