Two issues: (1) vibration and (2) airblast. The old US Bureau of Mines (now NIOSH) conducted many tests to determine the effect of vibrations on residences, concluding that peak particle velocity (PPV) of 0.5 inch per second is unlikely to cause any damage. Airblast rattles windows and doors...
A safe value for cohesion is zero. Analyse the problem and determine how much cohesion is required to keep the amount of reinforcement within reason. If you are using dowels, they are untensioned and do not develop strength until movement occurs. Is this what you intend? Is water present...
Concrete to rock 0.4, if the rock is sound and properly cleaned prior to placing concrete.
Rockfall netting seems a better choice, cheaper and more certain of result.
You might refer to "Theoretical Manual for Design of Cellular Sheet Pile Structures (Cofferdams and Retaining Structures)." The manual was produced by the Waterways Experiment Station of the Corps of Engineers in 1987. I don't know if it has been updated or if it is available online...
Maybe give a look at the following:
Slope Stability Problems Associated with Timber Harvesting in Mountainous Regions of the Western United States, USFS General Technical Report PNW-21, 1974 (has a good discussion about the relationship between precipitation and mobilization).
Earth Flows...
If the soil is not saturated, you might want to consider soil cement columns. Check with any ground improvement contractor such as Hayward-Baker or Soletanche for advice and cost.
Try "Earth Support Systems & Retaining Structures" published by Pile Buck, Inc. 407-744-8780. It has the answers you seek.
A couple of general references you might find helpful are (1) Chapter 4 (Brittle Failure of Rock) by Evert Hoek in Rock Mechanics in Engineering Practice by Stagg and Zienkiewicz and (2) Chapter 8 (Strength) by John Franklin in Rock Engineering by Franklin and Dusseault. On page 258...
A technique that might work in your application is sonic drilling. You can inquire by contacting Boart Longyear at the office nearest to you. The office with which I am familiar is located in Otis Orchards, Washington, 509-926-9576. Ask for Bob Buto or John Sine.
