Solutions: Weak Soil > Building Foundations
When building a wall, whether it is a basement wall or an outdoor
retaining wall, it is necessary to make it strong enough to resist
the pressure differential from the soil side to the open side. This
pressure will consist of two elements:
- Soil Pressure, which is a function of the soil depth and type
- Hydrostatic pressure, which will be simply the depth of the water table against the wall
times the density of water
The designer has two choices on what to do about hydrostatic pressure:
- Hydrostatic pressure can be factored in to the wall design, requiring
a wall at least twice as strong as would be required from soil pressure
- Hydrostatic pressure can be eliminated by providing a drainage
path for water adjacent to the wall.
It is much more cost-effective in most cases to provide a hydrostatic
pressure relief system. Today there are two basic types:
- Crushed Gravel: A clean gravel is placed against the wall as backfilling
takes place. This is a very slow labor intensive job with unpredictable
results. Furthermore, waterproofing membranes applied to the outside
of the wall can be damaged in this process.
- Synthetic Sheet Drain System: Some type of sheet drain is used.
Advantages of the
Insulated Drainage Panel for use as the part
of a Hydrostatic Pressure Relief system:
- It insulates the wall from the soil, saves energy if interior is heated, moves dew point to exterior.
- The flow characteristics can be predetermined by the designer
through their choice of thickness.
- The waterproofing is protected from backfill.
- The Insulated Drainage Panel will provide a degree of compressibility,
to mitigate the problems arising from swelling soils.