Retaining Wall

A good friends house has a 3 tier retaining wall about 50' from their back door holding back about 30' of the hill. The problem I am describing is affecting (5) houses in the row.
During a recent downpour the wall failed at the highest level and had the domino effect, the top fell, pushing level 2 down to level 1, etc. Needless to say it's a mess.
After checking it out I found the retaining wall was build as an upsidedown V from decorative stone and motar, no metal reinforcement was found in the damaged wall. Furthermore all the weep holes, 4" PVC at the lowest level still had small pebbles in them and I found a small piece of paper indicating that NO water had ever come from them.
As far as I can tell the backfill of each level was simply TX dirt with no stones etc to help drainage. To make matters worse my friends home is on the far right which happens to be at the lowest level of the slope from left to right.
Where can I find some information in regards to min requirements for a wall like this?
Thanks!
JimD
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I don't know about minimum requirements.
Are you looking for a solution? This will NOT be cheap or easy. There are multiple solutions, but under the circumstances I think you will need the input of a soils engineer. Traditional poured in place retaining walls strong enough to resist the hillside definitely must be engineered and will require major concrete work. There are many more recent segmental block retaining systems like: http://www.keystonewalls.com / Q&A section: <http://www.keystonewalls.com/pages/DesignPro_pages/DP_consdtls.html
Holding the new walls or saving the old might be helped by using these: http://www.earthanchor.com/mantaapp1.html
There is a new system that shoots soil nails into existing hillsides without the traditional grouting. This system shoots 1 1/2" bolts 18' long. http://www.soilnaillauncher.com /
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