CLSM Lateral Pressure
CLSM Lateral Pressure
(OP)
We are planning to backfill behind abutment and wing walls of a new proposed bridge with at least 320 psi (preferably 600psi) foamed CLSM (unit weight of 65 pcf). After it is set, what kind of active pressure it can exert to the walls in dry state. We have considered 4 Ft lift height during construction and have already considered horizontal pressure from the fluid CLSM. Your help will be greatly appreciated. Thanks.
RE: CLSM Lateral Pressure
RE: CLSM Lateral Pressure
Thanks a lot for your input. I agree with your view. However, there are people from an extremely reputed firm thinks otherwise. It will be great if I can present some evidence. Will you be able to get me some documents (research paper, guides, or past design performed on a live project, etc.). All I am getting over the internet is few old half done research paper.
Thanks once again.
RE: CLSM Lateral Pressure
if it was a chunk of 3,000 psi concrete or solid bedrock behind the wall, would there be any pressure? What if you left an 1/8 inch gap between the back of the wall and the CLSM, would there be any pressure then? So what if you precast the concrete, then placed it behind the abutment wall, would that cause any pressure?
Does it transmit some force from earth behind it? Will it allow water to build behind the wall to generate full hydrostatic pressure?
RE: CLSM Lateral Pressure
FYI. There will be drainage board behind the wall and weep holes to avoid any hydrostatic build up. There should not be any gap between the flowable fill and the wall backface as the fluid CLSM should fill up any voids.
Thanks for your input.
RE: CLSM Lateral Pressure
RE: CLSM Lateral Pressure
RE: CLSM Lateral Pressure
RE: CLSM Lateral Pressure
If someone believes there will be pressure from the CLSM, ask them to draw a load diagram explaining why there is load and the source of the load.
Mike Lambert
RE: CLSM Lateral Pressure
RE: CLSM Lateral Pressure
You are asking us to prove a negative, can't be done. You need to ask those who are stating that there will be pressure to provide a free body diagram showing the load. Then others can look at that diagram and determine where the errors/misunderstanding are.
Mike Lambert
RE: CLSM Lateral Pressure
See Page 6 of 8 for an example of what I have described. http://docs.lib.purdue.edu/cgi/viewcontent.cgi?art...
www.PeirceEngineering.com
RE: CLSM Lateral Pressure
I also agree that there is some chance that there is unbalanced earth pressure working on the back side of the CLSM. So is there sufficient shear strength to hold back the CLSM?
f-d
ípapß gordo ainÆt no madre flaca!
RE: CLSM Lateral Pressure
www.PeirceEngineering.com
RE: CLSM Lateral Pressure
This is the fill which will be covered by an approach slab (a structural slab designed to span between the abutment and another approach structure on one side and between abut and a sleeper pad on the other side). The flowable fill below should not see any load from above the roadway. The fill will be contained in a 4 sided enclosure (45 ft by 30 ft approx.) behind one abutment. On the other side geotechnical straps will be provided to retain the soil beyond the limit of wingwalls. So, there should not be any material that will induce active pressure on the fill mass. Also, the grade on both approaches slopes down away from the abutments/bridge.
Say the minimum compressive strength of the 65 pcf flowable fill is 320 psi. The shear strength should be 2*fc^0.5 (assuming concrete type property), which will be around 36 psi. So, self weight of the fill (max height 15 ft approx.) is the only weight that will have to induce a shear stress (along the sliding plane from the wedge above) greater than 36 psi to initiate lateral movement. Is it going to happen? It seems like the factor of safety is too high for this lightweight material. Even if we assume that there will be some residual lateral pressure, what will be a reasonable value? 35 psf equivalent fluid pressure seems too high.
Thanks for all of your active participation in this discussion.
Thanks,
MR
RE: CLSM Lateral Pressure
That said, I overstated in my previous post.
Really need a sketch to see what is really going on.
msrrr77 - you really need to have your geotech address this issue. I suggest that the first step would be a good sketch followed by a free body diagram to look at load paths.
Mike Lambert
RE: CLSM Lateral Pressure
Keep in mind that a 320 psi compressive strength is a lot if you think of it in lbs/sq. ft. like soil cohesion (1000's of PSF) which does not take much to reduce earth pressures to nothing.
BTW, You might be able to make a case that an approach slab is not needed if the the entire zone behind an abutment will be filled with the material. Not sure how it would settle differentially without cracking. More chance of the settlement to be behind the lightweight concrete fill mass.