Designing Rock Anchors

[weab]

I have been doing work for a mining company for about 10 years. The site engineers are steadily doing less and handing more over to us, an engineering consultant. I have been doing some inconsequential rock anchor designs with little loads. The client likes wall plates with 2 or 4 rock anchors and welding beams to the wall plates to provide lateral or vertical support.

What we use primarily are 20mm diameter anchors (rebar). I am not responsible for the grout or how deep they are drilled. However I would like to be comfortable in my designs.

I have been given a 5 metric ton working load capacity per rock anchor. I have been given a 1 page sample calculation for design of the rock anchor based on a working load. Basically, I must determine the maximum load using "square root of the sum of the squares" and compare that to 5 tons. This seem inadequate for design of structures involving life safety.

Also, sometimes I am given a situation to design a concrete structure to be anchored. Concrete is designed based on ultimate loads, but 1.6 times the 5 tons does not equal the capacity of a 20 dia rebar.

I want to design these safely. Is it really this easy? Is there more to it than what I've been given? If so, please provide for me a reference or something to point to so that I can tell the client that I need more information to design a complicated thing. Or tell me that I am over-thinking this.

Any help is appreciated.

 

[BigInch]

Concrete design is a different concept than the rock anchor design, as you note, based on ultimate strength, whereas rock anchors are based on safe working load. The numeric value of design loads don't have to be equal across those differing concepts.

From "BigInch's Extremely simple theory of everything."

 

[Kwazai]

I've wondered about this (as an outsider) because the thought of using an abandoned underground mine for a solar updraft turbine piqued my curiosity. the turbine would be at the top, solar hot water basically poured down a U tube to the bottom of the mine and convective upward air flow.
With a 'deep' mine steeper than 45 degrees it seems viable. however with the turbine at the top of the shaft it would need to be held down (uplift connection in mine shaft rock walls). Piping to the bottom would be secured for gravity loads.

Are there any reference materials available. (from one who is still trying to figure out how to read the mine maps of the mine under the Lonesome Pine Airport- a neophyte per se)

Mike

Murphys law 28th corollary- If there are five ways for something to go wrong, and you circumvent all five, a sixth will promptly develop.
Kwazai's addition- if you circumvent the sixth a seventh will develop, etc. etc.

 

[miningman]

This is getting a bit off topic relative to the original post , but you dont need any hot water to induce flow in a shaft. Provided you have two shafts, interconnected by some underground workings , the natural ventilation pressure can induce some very strong airflows , and these flows are typically stronger in the winter months because that is when the temperature differential is at its greatest