Foundation for one-side-formwork 3

I don't believe formwork is typically designed for the reaction of the entire form full with liquid concrete. Not even the wood form could handle that. I believe they are designed for a rate of pour that allows a certain amount to harden enough to support the next lift without compounding the pressure.

Another option is a forming system like this which designed for blind pours.

Another option is to install tiebacks into the soil (assuming its an earth retaining structure) behind. The tiebacks could have threaded rods that bolt through the forms to capture whalers.

Similar to what pvchabot is stating, get the formwork designer to verify/check the 42k/4' frame horizontal force.

If the pour rate was 11'/hour (way, way too high, but let's assume) then you would have 11' x 150 pcf = 1,650 psf at base, and this equates to 9k/ft at h/3, so over 4' frame width that equals 36k/4' horizontal force frame, so close to the provided 42k/frame value.

I would be placing this wall at less than 4'/hr, so about 600 psf MAX, so a lateral component of about half of 42k/frame.

yes.. you are missing something..

Although 42 kips per frame is too conservative , i assume the design load provided by formwork supplier.. You do not need passive thrust to resist horizontal load 42 kips.

The horizontal load is resisted by R1x and the OT moment is resisted by the couple R1y and P3y... R2 y will develop as vertical reaction prior to concreting and after concrete get hardened..

If we assume fresh concrete depth 11 ft , the width of the bracket from R1 to P3 is 5 ft and assume the horizontal fresh concrete load is 42 kips, and neglect the wt of bracket ;

- R1x will be 42 kips,
- R1y = P3y = 42*11/(3*5)=31 kips.

The diagonal anchor at R1 SHALL resist to 42 kips V, 31 kips H. loading ..

The following picture ( found at web ) explains the one side formwork concept

Sorry I forgot to clarify, all the forces in red are given by formwork supplier, which is based on a pour rate that limits maximum pressure to 1250psf.
R1x = R1y = 42kip
R2y = 29kip
R3y = 13kip
I think where I made it confusing is that the “R” forces are actually applied forces that I need to resist. I have yet to figure out how R1x can be counteracted as explained in my original post.

In my experience in the formwork industry, many one-sided jobs like this would consider the ACI minimum pour pressure of 600 psf, which requires the contractor to place the concrete much more slowly. I do remember some one-sided projects where the contractor needed/demanded a high pour rate, and the strip footing at the base needed to be enlarged to accommodate the higher reactions. However, I was never involved with the analysis of the footing itself, so I can't help with your fundamental question. But depending on the status of the job, it may be worth investigating if the lower pour pressure could be utilized.

HTURKAK said:

yes.. you are missing something..

You do not need passive thrust to resist horizontal load 42 kips.

The horizontal load is resisted by R1x and the OT moment is resisted by the couple R1y and P3y... R2 y will develop as vertical reaction prior to concreting and after concrete get hardened..

Click to expand...

HTURKAK: I think the OP understand that the reactions from the forming system are locally reacted by the concrete footing (diagonal cast-in anchors etc), but OP is concerned with the global concrete footing (as a mass) in resisting this temporary (albeit very short-term) action.

Yao1989 said:

which is based on a pour rate that limits maximum pressure to 1250psf.

Click to expand...

Yao1989: I think you need to get the contractor to reduce the concrete placement rate substantially. Maybe two placements, each of 11'/2 = 5.5'?

Dear Ingenuity, If the designer needs passive thrust of the footing to resist the unbalanced horizontal load of fresh concrete, he should be ready to accept a horizontal displacement in the range of 50 mm..

The horizontal load transferred to the ftg via the diagonal anchors shall be resisted by friction or balanced by counter load from the across wall etc..

The following excerpt ( Illustration of active and passive pressures with usual range of values for cohesionless and cohesive soil.) from Foundation Analysis and Design ( by Joseph E. Bowles )

HTURKAK said:

The horizontal load transferred to the ftg via the diagonal anchors shall be resisted by friction or balanced by counter load from the across wall etc..

Click to expand...

HTURKAK: The OP stated that with the applied dead loads (self weight of hardened concrete footing and wet weight concrete wall being placed) with soil friction at the base of the footing there was not of sufficient resistance.

I am not too sure what you refer as "across wall". May I ask you to explain? Thank you.

I think the placement rate has to be substantially reduced to make this work.

I have seen concrete counterweights ('deadman') used in some one-sided formwork situations, but they do not look like an elegant solution.

@HTURKAK: may I ask where you got took the graph in your last post from? That's interesting and I've not seen it before.

English is not my first language may be i should say a similar one side formwork at opposite side. If the OP provides full picture , we could see the applicable options..

I have the same opinion that if the total friction resistance can not provide FS against sliding , the placement rate should be reduced..IMO, the use of deadman could be an option if displacement of the wall surface is acceptable ..

Koot,

That chart exists in the Canadian Foundation Engineering Manual I believe.

I'm currently on holidays or I'd check for you.

EDIT - Wait...based on your DWG the SOG is already cast prior to the wall being formed? Why is that not taking our sliding pressure exactly?

EDIT 2 - Alright...maybe that is not a SOG? Would make more sense just it boxed out like that. Bah haven't had coffee yet! Anyways, alright so we still have a problem. Some comments!

A) Increase footing depth / add a shear key instead of making it wider to increase passive resistance
B) Grade beams from wall to wall or else props at base of wall should adjacent parallel walls be close enough
C) Big ass concrete blocks as Ingenuity suggested
D) Reduce pour rate to something manageable like 4-5' / HR if the wall is long enough (if it's short you'll never get the guys on site to wait for it to setup)

Yao1989, no, you are not missing anything. These one-sided wall forms do require a big, deep footing/block to resist the lateral pressure - unless you can use a smaller footing/block with some type of tieback anchor.

Thanks everyone for the feedback! Very useful info.

So I ended up asking to reduce pour rate to 4'/hr, and the reaction load has then reduced, but still 34kips or horizontal load to resist.

Seeing how much deflection before using passive pressure, I changed to use Ko at rest instead for soil pressure.
in below I have combined R1y & R2y into a single P1. long story short, even with reduced pour rate I still get nowhere close the sliding resistance. I'm pretty sure I have the correct free-body-diagram, so I guess one-side-formwork just need really robust foundations.

For my project I ended up asking the secant pile engineer if we can attach some D2L welded rebar to their steel secant pile to help resisting the horizontal sliding force. This makes most sense to me as now I have a situation that is almost like a tied formwork, except I only have a single tie at the base.