In UK we go with BS EN 1991-4:2006. Look for “Eccentricity” there are some calculations for it. You are right wall friction, internal friction etc. do play important role. ■

Three thoughts/plus questions come to mind;

No matter what you will have the total down pressure of the entire mass to deal with as gravity is still gravity.

If anything the weight per square foot will increase in relation to the cavity size. its all "Sir Isaac Newtons" fault.

Is this bin for a skip loader pocket with a hopper underneath feeding the skip loaders or is it for a screening plant surge pocket?

Are you using an apron feeder or a vibratory feeder for drawdown?

A vibratory feeder will vibrate and pack any small fines and in the process stop every thing above it left on long enough and the minor slope will be a magnet for build up especially with high moisture.

A very small apron feeder will do the job very well and eliminate the possibility of packing, bridging, honking or ratholing due to the movement of material in mass.

If you are using it for run of mine ore it will rat hole and bridge over definitely unless you use an apron feeder.

The problem of silo, honking, burping/mass sliding/mass movement of material when the material bridges also comes forward due to the crystaline structure of rock salt for both the R.O.M. salt and finished sizing.

If you are designing that thing for rock salt you are going to have problems due to the natural tendency for it to bridge and rat hole-due to the crystaline structure of rock salt; take it from someone who knows.

Are you going to rock bolt and install wire mesh on the walls and exposed bin surfaces of the silo/bin? what is the size of the opening/drawdown point?

How is the cavity to be mined and how big is it? Is it going to be shot from the bottom up or the top down with small diameter drill holes and a cluster of relief holes in the center of the shot design? ■

Greetings and salutations from my corner of the soon to be frozen eastern wilderness,

Judging from your drawing I will tell you that the forces are the same as you will have flow en mass.

How well the bin is mined out and repaired with mesh and rock bolts is somehting that MSHA will oversee and require proper construction for as there is a drawdown cavity under the orepass.

evrything will need to be rock bolted with either resin bolts or mechanical rock bolts.

Now that I see your drawing JSD it makes more sense ore passes of any kind are a "cock up" as my friend john would say as they are trouble magnets.

Your ore will move freely but I will suggest that you order a pre made hopper from a company that makes steel outdoor bins for gravel plants as they are tapered on all sizes "Erie" is or was a going concern" and the tapered bins are perfect for this-I will explain why in full.

First: by ordering a tapered hopper bin with a top opening wider than the ore pass you gain by eliminating any area for buildup as all of the ore must fall to the feeder floor.

Second: The ore will not flow over the edge of the hopper as the hopper edge is wider than the ore pass and can only pile on material at rest and not spill over. oversized recieving bins are used in bagging plants to allow for fast drawdown and to help with emptying the overhead bins.

The oversized hopper will also reduce cleanup as well.

It also nearly eliminates the need for entry and those risks-I will explain further.

The mine where I worked had a surge pile feeder for ROM salt and it was prone to plugging as the design was poor due to a flat bottom bin floor in rock with two vertical galvanized culverts for drawdown to a vibratory feeder feeding a 36 inch belt,- at first they had one culvert and they did not have very good drawdown-lots of plugging- and they did not pay attension to gravity. My closest friend was killed and another coworker died threee days later due to being brain dead from lack of oxygen.

I dont mean to digress but my uncles decision cost two men their lives.

If you do anything eliminate the shoulders surrounding your apron feeder in the drawing by ordering an oversize hopper larger than the drawdown hole/orepass diameter and you and the client will have zero problems due to the reasons above.

Sand and gravel hoppers come in lots of sizes so ordering one for this orepass will be easy and you will not have any headaches especially since you are using an apron feeder-the hopper can be designed with a apron feeder drawdown in the bottom of the hopper easily. and the outside hopper walls will be ribbed to add strengh and support to the hopper reducing the stress on the tapered side walls.

Good conveyor skirting for the apron feeder is a must of course

and the hopper builder can easily incorporate skirt boards and skirt board holders in the bottom of the hopper to fit the apron feeder.

If your client is in the USA they will need to rockbolt and mesh the walls(per MSHA) of the feeder so you will need to ask them about that as it will be easier to rock bolt and mesh the walls of the feeder from the bottom of the opening by using an arial man lift or scaffolding and staging.

Save your self a lot of work and headaches JSD as I can tell you even though I am a layman what works and what won't simply from my work experience underground.

lzaharis

please use my email off the board if you would like.

lzaharis@lightlink.com ■

The UK National Coal Board had a Standard for Staple Shaft Design (Underground Bunkers) almost as you describe. My copy had a bright orange copy but even so I can't find it for you.

Alternatively the Kallenborn catalogue describes lining methods for ore passes & underground bunkers do there might be something there to help you. The pressure on their bassalt tiles must be addressed in there somewhere.

Staple shafts have a spiral loading chute running down the rock wall for the material to roll down and reduce the drop height. This must modify the overall download & might do it along the lines you indicate.

Don't forget to drain the water away whatever you do. ■