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Part 3 Terraces - The economics of ecology
- Site Considerations
Site conditions effect all terrace projects differently, even when they are right next door to one another. The primary factor that must be addressed in a terrace project is soil conditions. Since a structure is being built to support the soil behind it, each terrace wall has to be sitting on firm, natural grade. As easy as that is to say, it can be difficult to find in some subdivisions where fill material has been piled up, dumped and/or re-graded from surrounding development. An additional excavation expense should be included if there appears to be a chance that fill material may be present on a project site.
Once this natural grade has been established, then comes the critical question: How many terraces and how high should they be? Most jurisdictions allow terraces to be constructed under 48 inches in height without a building permit. But should your project exceed the 48 inches limit or retaining a slope that exceeds a 2:1 grade, then a building permit often is required along with appropriate structural and/or soils engineering.
Example: Let’s say that you have a bank that from the toe to the top is 7 feet in height. What are your options?
Option #1: Your could create one terrace, 7 feet tall! This will require a building permit and engineering in order to build it. In the overall design of a project, you need to know that this will create a fortress look that won’t be easy to hide with other landscaping features.
Option #2: You could create two or more terraces using shorter walls. This option will work provided that you have enough room to allow space between each terrace. The general rule-of-thumb is that you need to have a minimum distance between two terraces that equals the height of the upper wall. If there isn’t room available then an upper wall will create a surcharge weight that will require the lower terrace wall to be engineered to support the upper wall.
One additional site consideration in the design of a terrace project is backfill. As mentioned previously, excavation is an integral part of any terrace. Try to design the placement of your terraces in such a manner that each walls excavated soil will be able to be used as backfill for that wall and the terrace area that it is creating. If this is possible, you can keep your backfilling -- as well as hauling expense -- to a minimum.
Equipment Issues
In new construction, there are not a lot of concerns about what equipment to use to create a terrace project. But in an established neighborhood, selecting the right equipment to complete the project is critical. Often, accessibility to the project site will be the main obstacle that will have to be overcome. This generally limits the use of larger pieces of equipment. A small trac-hoe is beneficial in projects of this sort since they don’t require a significant amount of space to maneuver around. A skid-steer loader is also ideal for moving material in and out of the site. With both of these pieces of equipment make sure that there is enough clearance for them to move throughout the project. Additionally, verify the location of any utilities and sprinkler systems that might be in the direction of travel or within the area of work.
If you are doing a lot of unit masonry wall construction then a must-have is a plate compactor. Most of these systems require that the gravel footing base be compacted. Also, there are the standard tools of the trade that we just can’t seem to get rid of: A pick, shovel and wheelbarrow. While you may try to keep away from manual labor as much as possible, some projects just can’t be done any other way.
After reviewing these factors it
might appear that creating terraces might not be worth the trouble. Yet as with
most processes in the construction industry, it takes longer to explain it then
to just do it. The rewards from customers and local municipalities of a
successful terracing project will surely propel you on to creating more
diversity in your projects.
Part 1 - Introduction
Part 2 -
Materials
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