NPK IS THE LEADER IN RETAINING WALLS:
Construction and repair for the Bozeman area. We are able to construct walls out of all different types of materials. From boulders, stone, manufactured block, wood, and concrete.
Here is an image (with terminology) of the different type of walls that can be constructed.
The type of wall you or your contractor chooses is dependent of factors such as the height of the wall, the soil load behind the wall, where the wall is located, soil under the wall(stability issues), and appearance to name a few.
Most retaining walls in the residential and smaller commercial projects are either Gravity walls, or Anchor walls(wooden wall with deadman, or manufactured block with geogrid). This simply comes down to cost, and the size of the walls being built in this arena. Generally they do not become large enough to necessitate using the other wall types.
It is extremely important that whoever you hire to construct your retaining wall. That they have the knowledge to properly choose the correct type of wall to build for the situation, and have the knowhow to go about it correctly. The last thing anyone wants is to spend money, time, and energy having a wall constructed just to have it fail a few years later. Then hoping the contractor is still around, and will guarantee their work.
At their root retaining walls are simple structures, however if you start to look around town you may see a lot of existing walls that are bulging, leaning, or have failed. There are many reasons a wall might fail, but generally it comes down to either poor construction, or old age.
Poor construction can come in many forms. Such as improper wall weight or anchor system to the soil load behind the wall, improper drainage system, incorrect base construction, or improper back fill techniques. Any one, or combination of these can result in wall failure.
An image of the different types of possible failures:
Besides old age preventing wall failure is pretty simple. Just take the time to build it correct in the first place!
That is why we feel it is extremely important to hire a qualified contractor. Sometimes(but not all) building a wall correctly is not going to be the cheapest option. You may run into a contractor that isn’t aware of proper techniques, so they may skip vital steps in the construction process. Once the wall is built you cannot tell what they did under(base construction), or behind(backfill, anchor, and drainage) of the wall. It may appear to be a solid wall, but wait a year or two and things may begin to fall apart. In skipping certain steps in construction they can provide a cheaper price because they are not doing as much work or using as much product. Which makes the overall project price less expensive.
However, in the long run this is going to be more expensive than building it correct in the first place, because you will begin to have costly repairs and may have to build the entire wall over again if you experience complete failure.
Some build basics are:
1. Dig the soil down to 3″ to 12″ inches below where you want your base layer to start. This is dependent on many variables, but you need to start with a flat area the length of the wall.
2. Dependent on the wall type you will need to create a base layer of “roadmix” crushed aggregate gravel, or a concrete footer.
3. Lay down your first layer of wall build material – stone, block, etc..
4. Once that is done lay landscape fabric behind the stone and up the side of the hill.
5. Install a perforated drain tile the length of the wall at the base layer. Make sure this drain tile slopes from high to low.
6. As you build the wall you will be adding clear washstone as backfill. Shovel in backfill as you build the wall, one tier at a time. Don’t add all the backfill at the end—it won’t compact thoroughly. Tamp down the washstone as you go with a hand tamper. Behind the top tier of the wall add about 6 inches of topsoil.
Some of the different types of walls, and picture examples are discussed below: