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.