Lateral earth pressure on pole 2

[canwesteng]

I have a large pole (say 2 feet in diameter) standing in a pile of bulk material. If half the pile is emptied, how would I calculate the lateral pressure from the remaining pile on the pole? And what might the pile look like?

 

[bridgebuster]

The same way you calculated the pressure before removing the pile. I imagine you would have treat the pile like a berm. You can look in the US Navy Manuals, I recall they have info about berms to support embedded walls, which doesn't quite sound like your situation. It becomes an iterative process to determine when the pole will fall over; be conservative in your approach.

The best thing is to ask a Geotech. Otherwise, don't touch this with a 10-foot pole.

 

[r13]

Without knowing the configuration, I assume it is similar to earth pressure calculation, you need to know the friction angle of the bulk material, then it may require a slop stability analysis.

 

[canwesteng]

It's basically a pole in a pile of sand, forming a cone when full. Loaders will remove sand from one side, potentially creating an imbalanced load condition?

 

[BridgeSmith]

Your 'retained backfill' height can conservatively be taken equal to the tangent of the angle of repose of the material, multiplied by half the circumference of the pole. The geotechs here may have a less conservative estimation, but if it was me, I'd use the passive soil pressure to calculate the load in the situation you describe.


Rod Smith, P.E., The artist formerly known as HotRod10

 

[r13]

Depending on the other side (behind the remaining pile) is blocked, thus restricts the material flow, or not. If the sand is enclosed in two rigid supports, then active pressure will develop. However, if it is allowed to slide freely, then the active pressure will be reduced. If you remember how to do a wedge analysis, this is the case.

 

[azcats]

Say the loader removed a scoop directly behind the pole, would there be a be a short term higher surcharge while the sand redistributes?

 

[BridgeSmith]

I think you'd have to consider this like you would a pier in a landslide zone, albeit a very small one; that's why I suggested passive soil pressure. Would that not be the analogous condition?

Rod Smith, P.E., The artist formerly known as HotRod10

 

[canwesteng]

I've approached it as a wedge analysis as well. Seems somewhat conservative

 

[r13]

This is how I see it.

 

[r13]

If the graph depict the situation correctly, the maximum pressure the middle pole can experience is at rest pressure, if the pile on the right chamber stay long enough. And the pole will experience passive pressure only when the loader pushes the pole into the pile on the right chamber. Even with that, the pressure is short lived, as it would rebound back to the original position, thus release the pressure.

If the loader start to work on the full pile on the right, then the pole suffers active pressure plus a vehicular surcharge load.

 

[ldeem]

You might try looking at stacker tube design.

http://civilwares.free.fr/ACI/MCP04/313_97.pdf

This has a few notes but may be enough to get started.

One thing that has always surprised me in designing silo's, bin's etc. is the loads that can develop from material flow. Retaining wall concepts are static so may be understating the actual loads as material moves along the pipe.

 

[canwesteng]

That's absolutely brilliant. Eng tips never fails to deliver.

 

[PEinc]

How do you think you are going to keep a full height of granular soil behind a single 2' diameter, vertical pipe when you dig to remove soil from in front of the pipe? Won't the "sand" just run around the sides of the pile? Also, you will have little to no passive resistance when you excavate a slope, probably to the sand's angle of repose, in front of the vertical pipe. IMO, if you dig in front of the pipe to the sand's angle of repose, the soil around and behind the single pipe will slough or run to the same angle and you will not have any lateral pressure on the pipe. What is the function of the pipe or pipes?

http://www.PeirceEngineering.com

 

[canwesteng]

The pipe is just to soft drop the sand. I have no desire to retain any soil at behind the pipe, I just want to make sure the pipe doesn't fall over.

 

[mfrad]

I agree with PEinc. In fact there is no lateral pressure on the pipe since it will only tilt. Stick a wooden matchstick in container with sugar and "excavate" out one side. The angle of repose will develope initially on one side. The surface elevation of the sugar will become lower and flow on a slope per the angle of repose. If the pole is top heavy it will fall over.

 

[r13]

If the pipe is fixed on the floor, there will be pressure build-up. If the pipe is free standing, unless the stockpile is filled uniformly around the pipe, it will tilt.

 

[PEinc]

Tilting could be a function of how quickly the sand is excavated and how gradually the sand is allowed to seek its angle of repose.

http://www.PeirceEngineering.com

 

[r13]

If no base connection with structural rigidity, the pole is a floating body, it can tilt in any manner, or speed, depends on how the bulk material is placed around.

It is similar to the pier in a river, the upstream pressure is increased above head due to dynamic effect, the downstream pressure is lowered due to loss of head by drag. The speed of flow is important, but foundation must be present, otherwise the pier will be washed away by the river flow.