We are considering building a wall to retain a bank. Have seen timber walling used before. Want to find out method of construction in my own time and without commitment to supplier/manufacturer. Was hoping there would be somewhere on the web to help.
Given favourable ground conditions was hoping there would be information giving different heights of wall and their thicknesses, i.e 1m high Xcm thick, 2m high Ycm thick etc
You're dealing with a fairly complicated subject; whole textbooks have been written on the subject. You would be better off hiring a good local geotechnical engineer to help you. S/he can save you a lot of time and headaches. There isn't a lot that we can do in terms of on-line help with the very little amount of information you have provided.
River banks are particularly tricky. (You used the phrase, to retain a bank - it sounds like you are dealing with a river bank.) You have to consider not only the dimensioning of the wall for lateral loads, but also erosion, bearing capacity - and slope stability. Simply dimensioning the wall for the expected lateral forces is the easy part...
If I have misunderstood your problem, I apologize. Please provide additional details.
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Thanks for such a quick response. The bank is effectively the change of ground levels. Everything is stable at the moment. The reason for wanting to erect a "structure" is to define boundaries and landscape what is currently untidy.
Below the bank is solid ground. Above the bank will be gardens.
All we were hoping for was a no obligation ball park guideline, if possible.
For the simple cost, why not hire a local geotechnical engineer. He/she can then provide a few recommendations as to options and save some headaches for you. Without looking at the site, it is nearly impossible to provide you with information that will be useful. Most comment will generic and vague because an experienced and trained eye may see something that, unless remedied, could be a potential hazard or detrimental to the project.
I agree with [blue]KRSServices[/blue] - you need to hire a local geotechnical engineer. If your bank was only 1.5 meters or less in height, we could point you in the right direction. But 7 meters? That's a major design effort - with significant risk to lives and property if it fails. I go back to my second post: would be better off hiring a good local geotechnical engineer to help you. To do otherwise is to court disaster -
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my rule of thumb is that any wall over about 3 or 4 feet requires a structural stability analysis and input from a geotech on the allowable bearing pressures on the soil and active/lateral earth pressures. Less than that, there are often standard designs available.
One method you might consider is a stepped back wall. Four feet high timber cribbing, step back about Four feet, another Four feet timber cribbing, step back, etc. Still, you would need some advice from a geotech on the width of the terraces and the effect of the surcharge on the bottom wall.
jim7,
A 7 meter high retaining wall is not a do-it-yourself home project. Talk to one or more contractors who specialize in designing and building retaining walls. Are you building a wall and backfilling behind it or are you excavating to build the wall? The first wall may require a Reinforced Earth wall, a segmental block wall with geogrid reinforcement, a series of terraced low gravity walls, or some other type of precast concrete gravity retaining wall. The second wall may require a tiedback or soil nailed wall. Different contractors specialize in different types of walls. Most consulting geotech and structural engineers do not specialize in any of these types of walls. I would start with an experienced retaining wall contractor who has in-house design capabilities and licensed engineers. The contractor will be able to get any required testing or design parameters needed. Be prepared for a very expensive cost estimate. If the wall has a relatively small exposed face area, the price per square foot will be expensive and contractor interest may be low. If the wall has a great face area, the unit price will drop but the total price and contractor interest will become great.
I agree with PEinc, I also don't like the look of timber walls, but that is personal. As I work for a geosynthetics company that also provides design assistance and have access to loads of software, I agree that you should consult with those who deal with these types of situations on a daily basis. Local segmental retaining wall licensee's usually will do preliminary designs for you as well, and have a relationship with a consulting engineering firm who can do final designs. Another option is a gabion faced reinforced wall.
Why not gabion walls - these have a long history. For timber cribs, I believe that Tschebetariof's book has a good section on it.
I agree that 7m high walls are not "run of the mill". What do you do about 13m high walls with designers "assuming" that there's no problems!!! I'm in the middle of it. Trying to bathe in grease for all I'm worth.
Done right this is going to be very expensive. Reinforced earth is the standard these days but you would not be able to do this kind of wall as a do it yourself. A rule of thumb is you need reinforcing every third course of block extending back 2/3 the height of the wall. Select backfill is also required (gravel). You would thus need to excavate 4.3 meters behind the wall to install the reinforcing fabric. For a 7 meter wall that is 119 cu yds of backfill every 10 ft. At $20 a yard the cost of backfill alone would be $2200 every 10 ft. You could die if there is no shoring in place, be very careful.
If you approach this as terracing, not as a monolithic 'retaining wall', it becomes a bit easier.
If you propose to break the elevation into 3-4 foot walls, each higher level set back 6-8 feet, you might find the audience a bit more receptive.
If you are attempting to gain more area at the lower grades you should reconsider the suitability of the site.
You should also accept the loss of area at the top of the hill. If you cannot accept these trade-offs, then don't do it.
If you are simply attempting to take a steep hillside and 'square it off' to allow easier maintenance, there are thousands of years of experience to learn from.
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