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Requirements of Underground or Basement Walls

requirements of basement walls

requirements of basement walls; Image Courtesy: Anderson Homes

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Understanding the basic requirements of underground or basement wall construction helps to attain durable basement walls with minimum maintenance. These basement walls are subjected to different forces and loads which will require standard design and construction practice to achieve the desired quality. There are certain functional requirements every underground or basement wall must possess to attain durable service period.

Functional Requirements of Underground or Basement Walls

Underground walls must support the following functional requirements whether it is in a framed structure or a load bearing structure. They are:
  1. Structural Stability
  2. Durability
  3. Moisture exclusion
  4. Insulation
  5. Proper Backfilling Method

Fig.1. Load and Moisture action on Underground or Basement Walls

1. Structural Stability 

The underground walls are subjected to high pressures, both axially and laterally. The lateral force exerted by the mass of earth which surrounds the walls can have a considerable effect, particularly in the case of walls to deep basements. Following requirements must be satisfied to maintain structural stability
  1. The lateral loads must be adequately resisted to maintain the stability of the wall. This is generally done either by bracing the walls or by constructing walls that are sufficiently robust to cope with the stresses involved.
  2. To resist the loading, bracing walls can be constructed below ground level with temporary supports or utilize the floors of the buildings as permanent braces. Walls can also be constructed to minimize the ground pressure by bracing them gradually as the work proceeds.
  3. The basement slabs are subjected to water table pressure. It is required to provide a 4-inch layer gravel beneath the slab to provide proper drainage.A pathway to relieve this water must be planned and constructed.

2. Moisture Exclusions 

Construction of basement walls in areas with high water table lets moisture and salts to interfere with the construction process of the building. This will affect the durability. These problems create restrictions on the nature of the construction of walls below ground level and it is particularly important in the case of the basement to be used as internal building space. To exclude moisture:
  1. Materials with low porosity are to be used. Porous materials absorb moisture from the ground and expand on freezing, causing spalling and friability of the material. Non-porous materials also tend to perform better in terms of moisture exclusion, since they do not transfer moisture through capillarity.
  2. Provide Water proofing membranes or damp proofing
  3. Provide proper water drainage systems

3. Durability 

The most important concern in underground or basement wall durability is the moisture penetration. As these structures are constructed deep into the ground, they are exposed either to high-water table levels, ground moistures, and salts. These concerns are an issue during the basement construction and if proper treatment is not provided to the basement, the issue sustains throughout the life of the structure. The durability requirements of underground or basement walls are:
  1. Dampproofing or waterproofing basement walls
  2. Design and construction of impermeable and dense concrete walls
  3. Use of construction materials that are less porous
  4. Instead of normal drainage, a perimeter footing drainage system can be constructed. This helps to relieve the hydrostatic pressure.
  5. An exterior and interior drainage system are recommended by experts
  6. The drainage must be properly connected to an outlet

Fig.2: Interior and Exterior Drainage System for Basement Walls; Image Courtesy: Concrete Network

4. Insulation 

An insulation to the basement walls helps to protect the waterproofing membranes provided to the walls. This insulation will help to reduce the expansion and contraction taking place in the wall membranes due to changes in moisture conditions. Insulation reduces the potential for cracking. This helps to increase the durability of wall membranes.

5. Proper Backfilling Method

Once the basement wall is constructed, the backfilling process must be started from the corner in a slow process. The soil pressure must be evenly distributed on the exterior walls of the basement. Use of small equipment help reduce the pressure of soil on the walls. Use of heavy equipment can create large pressure and result in structural cracks.

Fig.3: Backfilling of basement walls; Image Courtesy: Concrete Network

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