Replies

1. 
   Rein_Taul | Aug 10, 2001 05:40am | #1

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   That is pretty high.
   Will it support the driveway or will it hold earth back from the driveway?

   Supporting the driveway means you will have to support whatever drives on it too. I would be concerned about timbers holding back a cement truck someday.

   If you are excavating the area, think about adding geogrids for the highest parts. They are a lot of work, but not expensive. They can add to the lifespan of the wall.

1. 
   David_Thomas | Aug 10, 2001 06:09am | #2

   *Could you put the 6x6's out a little further and put the 2x10 BEHIND the posts? So as not to rely on the screws. Then placegeotech fabric on the soil, backfill with gravel, and drill weep holes in the bottom. -David

1. 
   Robert_Villa | Aug 10, 2001 05:26pm | #3

   *JLC just had an article on retaining walls. Read it.

1. 
   Erik_Johnson | Aug 11, 2001 04:38pm | #4

   *Jack,I'm a civil engineer. I was also a carpenter for about four years before I went to college. In my experience there are many things in life which are certain. Among them is that wood splits, concrete cracks, and the bigger you build something, the more of a monument it is to your ability to make decisions. A seventy foot wall is going to cost you easily over $1000 - maybe over $2000. You will probably spend 40 to 80 man hours to build it. My gut feeling is that if you only sink in the ground 50% of what you have in the air, it will start to fall over within a year or two. - water is a powerful factor in the design of retaining walls. I strongly suggest that you find a good civil engineer and get him to run the numbers and sketch a simple drawing for you. It shouldn't cost you more than $150 to $200, and it would be money well spent if you follow the plan. The little extra money will be saved when you don't have to replace it in the near future or have to go to counseling or the doctor because of the added stress your going to have just thinking about it.There are four major factors which are going to drive the design of your retaining wall: height, soil type, the live load (cars) and water. It is true that you should always provide a retaining wall excellent drainage, because that is ultimately what will push it over. Tie-backs aren't going to be enough unless you make them very long. An engineer will help you determine how far will be enough.Good luck!!

1. 
   Luka_ | Aug 11, 2001 08:50pm | #5

   *I went through a lot of head scratching a few weeks ago, when I was thinking about putting in a couple of retaining walls, myself.My biggest concern was cost, followed closely by time and effort. I finaly figured out that I didn't need to put one in. But before that, I went through several ideas before I finaly decided on going with one that closely resembles what Ma Nature would do her own self.I am not going to do one now, or if I do, it will not be as extensive as it was going to be. But here is the plan...Instead of making a vertical wall, having to pour a footing, and doing all the anchoring and other work and expense involved... Fill in the area as you want it. Leaving the outside edge of it at about a 20 to 30 degree angle. Now, pile large stones on the slope. Stones about the size of your head or bigger are best. Pile them in such a way that the pile ends up wider, (thicker), at the bottom, than at the top of the slope. The resulting slope should be more like 45 to 50 degrees.You could fill in the spaces between the rocks with gravel, to keep your dirt from washing away through the rocks.Here is a pic...

2. 
   wildone_ | Aug 13, 2001 12:25am | #6

   *Jack,Have you considered using one of the concrete block retaining wall systems? They will last more than twenty years and will not require concrete footings at least the ones I am familiar with. They have been engineered to meet various soil and site conditions. The manufacturers rep. will provide you with application info. We have not discussed soil type have we? Soil stability will have a factor in how you do this. An engineer or architect involvement may be a good idea depending on soil conditions. I believe a concrete block wall will add long term value to your property. In any case you need to provide a way for water pressure to weep thru your wall. That can be done by digging out an additional 12" behind the wall. Placing a landscape fabric against the dirt and fill in the space between the wall and fabric with 1-1/2" clean rock. The clean rock will allow the water to wick thru the wall and the fabric will prevent dirt from clogging the clean rock. A geogrid behind the wall anchored to the wall and embedded and anchored in the dirt will add to wall stability.Good luck.

3. 
   Ian.D.Gilham. | Aug 13, 2001 02:01am | #7

   *There is another way, which is to reinforce the earth backfill.Consolidate the backfill in 12" layers and on top of each layer, along the edge, lay plastic-coated diamond mesh fencing.The method is used on motorway embankments.

2. 
   Jack_Stanton | Aug 13, 2001 02:01am | #8

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   I am a trim carpenter and am going to build a retaining wall to extend my driveway . The wall will be 70 ft long and 7 ft tall at the highest point . I want to use treated 6x6s put 4 ft on center , set 4 feet into the ground for posts . I am thinking about screwing treated 2x10's to the posts horizontally all the way up .
   Since the back side of the wall faces into the woods I can run diagonal
   bracing on the back side ,which would be additional 6x6s set into concrete footings . And of course plenty of deadmen or tie backs . I did a few walls out of railroad ties in the past but they are so expensive in my area. The excavators on my jobs say this will be plenty sturdy and should last 20 years . I wanted to go with poured concrete but once again the price is just way to high . Has anyone used this technique ?? Warnings , Horror storied would be appreciated .