Phi angle for wet concrete?
Phi angle for wet concrete?
(OP)
I'm looking at a steel sheet pile cell design that may require tremie concrete cell fill due to concerns with vessel impact.
Does anyone have any information regarding the phi angle of wet concrete? I'm trying to determine the earth pressure coefficent for the design.
Thanks!
Does anyone have any information regarding the phi angle of wet concrete? I'm trying to determine the earth pressure coefficent for the design.
Thanks!





RE: Phi angle for wet concrete?
RE: Phi angle for wet concrete?
RE: Phi angle for wet concrete?
RE: Phi angle for wet concrete?
RE: Phi angle for wet concrete?
This might be related to when soils compacted against a wall give high lateral pressures because they yield during compaction, and some of the stress is locked in. The aggregate acts as a granular material that is not completely fluid.
Or maybe not.
RE: Phi angle for wet concrete?
We placed numorous instruments in two different pours and the measurments showed higher than Ka=1 conditions. Not for a long time but the pressures did spike during placement and vibrating.
RE: Phi angle for wet concrete?
the vibration is what i've always seen cause problems during wall placement. it depends on the things peinc mentions above. check out ACI 309 for info regarding the vibration and effects of vibration on concrete. for tremie placement, i visualize that there would be additional forces due to the pump itself pushing the concrete to displace the water....but i'm getting out of my area of knowledge so i'll leave the discussion to you folks that are more experienced than myself.
RE: Phi angle for wet concrete?
RE: Phi angle for wet concrete?
RE: Phi angle for wet concrete?
RE: Phi angle for wet concrete?
RE: Phi angle for wet concrete?
RE: Phi angle for wet concrete?
If you have concrete with a slump of 6 inches, doesn't that imply that there HAS to be a friction angle? Wouldn't that also imply that the friction angle would be pretty high (again, I may be misguided)?
To me, there is a liquid component to the wet concrete, but there is also a fair amount of aggregate that will develop internal friction. With this internal friction, there should be a corresponding affect on the lateral "earth" pressure acting on the retaining wall. I've never studied this at all (so again, I may be misguided), but it does lead me to wonder. . .
f-d
¡papá gordo ain't no madre flaca!
RE: Phi angle for wet concrete?
RE: Phi angle for wet concrete?
RE: Phi angle for wet concrete?
f-d
¡papá gordo ain't no madre flaca!
RE: Phi angle for wet concrete?
i don't know the answer to the question(s) at hand but thought i'd throw in my field experience from a past life to add to the discussion. i'll leave the remainder of this discussion for those more knowledgeable than myself.
RE: Phi angle for wet concrete?
We should remember a little bit about what we are talking about here, for Ka to be equal to or greater than 1, what we mean is that the lateral pressure is equal to or greater than the vertical pressure. i.e. both c, and phi are = to 0, not just phi, in other words the concrete acts as a full fluid which by definition has no shear strength. For concrete to have any slump it must have some internal strength that acts agains shear forces. It would either have to be adheasion, cohesion, or surface tension to prevent it from flowing our completely to fill its container. Since we are all comfortable with the terms of phi and c that is how we are describing it but that may not really be the correct terminology to describe the forces acting within the wet concrete.
So for us to say that Ka was measured to be greater than 1 what we are saying was that the horizontal pressure measured was higher than the static unit weight of the material. i.e. if we have a concrete with a wet density of 150 pcf then the hoizontal pressure was greater than 150 psf. The only way to get such a pressure is if we have placed concrete in the formwork and as we vibrate it we are inducing the pore pressure to exceed the overburden pressure and create a quick condition where the interlocking forces of the aggregate etc. are exceeded and the aggregate are floated like we see in liquefaction. When the pore pressure is raised then we may feel a higher pressure on the load cell placed on the forwork, than we would expect in a fully static fluid condition. But we should remember that this pore pressure will act in all directions equally so the ratio of actual pressure in the region of the vibration for hoizontal to vertical would not exceed 1, so therefore Ka trully does not exceed 1, it just seems like it.
If you are concerned about the additional pressures on your forwork, than in you design just add a few feet to the fluid height you have chosen for design to add some conservatism to it. Usually the reason forwork was blowing out was that the rate of placement greatly exceeded that of the design, and so you would have much more that 4 feet of concrete pressuring the forms.
RE: Phi angle for wet concrete?
Excessive vibrating can cause problems with concrete forms. However, I don't believe that designs should be made overly conservative just to account for any possible sloppy field procedures. In my opinion, contractor supervisors, inspectors, and quality control personnel should control improper field procedures - not designers.
RE: Phi angle for wet concrete?
Dik
RE: Phi angle for wet concrete?
The manual also references Lateral Pressure Design Formulas contained in the Americam Concrete Institute's "Guide to Formwork for Concrete, (ACI 347 latest revision)."
RE: Phi angle for wet concrete?
RE: Phi angle for wet concrete?