A retaining wall has one function, to hold back the weight of the soil and rock behind it. Soil, like any granular substance, will always seek to return to its original position. The retaining wall must prevent this movement and keep the backfill in place.
Only a wall of sufficient size can exert the lateral force needed to prevent the wall from sliding or overturning. So, what factors determine the size of the retaining wall?
Retaining Wall Height
The taller the wall, the more weight and force it will bear. Higher walls need stronger retaining wall materials and more complex foundations.
The Underlying Soil
Soil and rock have different weights and load-bearing capacities. Clay soils, for example, have a higher weight-bearing capacity than sandy soils. Likewise, solid rock has higher weight-bearing capacity than loose gravel. Retaining walls must be designed and built to accommodate the underlying and backfill conditions.
Retaining Wall Materials and Foundations
The retaining wall foundation is a primary factor in determining the appropriate wall size. Sometimes the foundation is designed according to the retaining wall materials. For example, a poured concrete wall typically has a cantilever foundation designed to use the weight of the soil to hold the wall in place. The base plate is usually about 70% of the height of the wall. The result is a narrower wall that takes less space.
A wall built from concrete blocks may not have a cantilever foundation, depending instead on gravity to provide the strength to hold the natural forces at bay. If this is the case, a larger, heavier wall is necessary. Xpress Engineering always designs walls with cantilever foundations for this reason.
One of the biggest causes of retaining wall failure is the accumulation of water behind the wall. Water increases the retained weight, so the provided drainage must be efficient. Drainage is delivered by weep holes or a drainage pipe behind the wall.
Surcharge loads, like buildings, concrete surfaces, swimming pools or parking, increase the load on the wall. The engineer must also factor in wind loads, hydrostatic loads and possible seismic activity when designing the wall size and foundation.
Call Xpress Engineering for quick and inexpensive engineering designs for retaining walls and make sure that your wall has what it takes to bear the load.