Retaining Wall For Trash Question 2

[starcasm]

This is my first post here so please bare with me. I didn't think this belonged in the Geotech forum because it's not soils that I am dealing with.

I have a retaining wall problem that I could use some guidance on. It's not a typical retaining wall that involves retaining soils. It is a wall that needs to retain trash. There's an open bay door about 28 feet wide that is being filled in with precast planks. The precast design and connection to the columns is not the issue in this post. I need to calculate the worst case uniform load which would act on the bottom most plank. The angle of repose for the trash is about 45 degrees. The density of trash that I am using is 25 PCF to be conservative. I couldn't find alot of information on that. I was looking in my references for some guidance and found examples of retaining walls that dealt only with soils and no angle of repose. It's throwing me off and it shouldn't. I believe there's got to be an easy solution to this. Could someone point me in the right direction?

Here's a sketch for reference.
Thanks in advance!
Daniel...

 

[parrot77]

Excuse me starcasm but I'll have to convert this to SI units as I am in Ireland. The density 25psf = 4 kN/m cub. Is this not small? Anyway the coefficient active pressure is 1-sin 45/1+Sin 45 = 0.2 The pressure at the bottom of the bottom plank in SI units is 0.2*4(kN/m cub.)*10.05(Height in m)= 8.04 kN/m sq= 16.8 PSF. The infill plank will not be fixed along its lenght at the base.Depending on the width of the plank therefore it may be designed for 16.8 PSF or the pressure may calculated at the top of the plank by varying H and an average load taken. Note safety factors should be applied to these loads

Incidentally the factored bending moment will be in the region of 102 kNm/m... well within the range of precast planks.

Once again I would say check your chosen density and angle of repose.. 45 degrees seems large.

Best of luck

 

[hokie66]

The hazards of switching back and forth between unit systems. Parrot77, you lost a decimal place. 33 ft x 25 lb/ft3 x .2 = 165 psf.

The density and repose angle quoted may be realistic for loose landfill material, but I don't think that would be the controlling condition. I imagine this as some sort of refuse transfer station, and think the appropriate loading would have to consider the loading from equipment placing the material and recovering it, etc. I have seen D9's operating in these stations.

 

[parrot77]

Ouch your right hokie66!!! Dont really have a feel for the empirical units. Sorry guys.

Ye regardless of machinary or parameters it seem a very light load to be taken at the bottom of a 33ft wall. If machinary is working on top of the trash and not just at ground level shoving it in /out surcharge will be present. This surcharge loading will be of far greater magnitude than that of the trash as hokie66 has suggested.

Hope you have gained some indication on how to approach the design starcasm

 

[starcasm]

Thank you for the replies! Parrot77, you are correct that the precast planks would not be fixed along their lengths. The unit density for trash is small. But if you think about it. Water has a unit weight of 62.4 pcf. If this trash were put in bags (poked with holes), it would definately float on the water.

The material is shredded and pushed by conveyor through an opening in the precast plank wall I am designing. Only a minor surcharge would be present which would be the weight of the grapple that runs on a monorail. There would be no other machinery on that side of the wall because there is another 40 foot of trash below the opening that I need to fill with precast planks. But that surcharge is a good point!

Thanks,
Daniel...