Digging a hole for a basement is not as simple as picking up a shovel or starting up a backhoe and digging out some dirt. Basements are parts of homes and buildings that are fully integrated into the building's structure. As such, the basement must be constructed well enough to help support the rest of the building above. Techniques for excavating basement holes vary and may be adapted to the particular situation of the builder.
When attempting to select the proper technique for excavating a basement hole, one of the primary considerations is the type of soil in which the basement will be constructed. Soil sliding is a common problem faced in basement excavation. It requires proper planning and supervision. Toppling is another common problem that occurs when stress fractures appear in the walls, causing the soil to topple over into the hole.
Protective Support Systems
Because of the potential problems associated with soil sliding and other forms of collapse, any type of digging technique for excavating a basement must have some type of protective support system in place. These generally involve creating retaining walls, or benching, the sides to avoid collapse. It can also involve creating some type of shield around the area in which workers are performing their duties. Another common technique that relates directly to digging involves sloping the sides of the hold so that they do not form an angle of a horizontal-to-vertical ratio greater than 1.5 to 1.0.
One way to safely dig out the hole for a basement excavation is to use the island method. This involves a partial excavation in which the central core part of the basement is built first in the center. From there, the outer walls of the basement are sloped until they can be properly braced and fully constructed. The outer walls are eventually braced by the completed inner structure until the entire basement is complete.
The top-down method of construction for basement excavation is one that is often used in large cities or congested areas. In the top-down method, the load-bearing walls of the basement are constructed and the ground layer slab is poured above where the basement will go. The building may even be fully constructed prior to the completion of the basement itself. The basement is not dug out completely until later, when the building and its foundation are fully in place. This method basically involves carefully digging out a portion of the ground below the building.
- Deep Excavation: Support Systems for Deep Excavation
- Builders Websource: Principles of Residential Drainage and Basement Waterproofing
- North Carolina Department of Labor: A Guide to the OSHA Excavations Standard
- Build Your Own House: How to Dig a Basement
- Middle East Technical University: Deep Excavation
- City University of Hong Kong: Excavations and Basement Construction
- Photo Credit Jupiterimages/Photos.com/Getty Images