Reinforced soil is the combination of compacted earth fill with tensile reinforcement to create an earth structure. The properties and performance of this earth structure depend on the bonding between the soil and reinforcement. The layout of reinforcement is done between the layers of compacted earth fill, which is an essential part of the construction process.
The reinforcing elements may be metallic, polymeric or even natural materials, but usually they are prefabricated in the form of strips, grids, meshes, webbing, nets or fabric sheets.
Principle of Reinforced Soil
The principle of reinforced soil is that an introduced material provides a tensile restraining force that reduces the lateral stress required to maintain the equilibrium of a loaded soil. As and when the soil element is compressed under vertical stress, it undergoes lateral deformation.
When the reinforcement added to the soil in the form of horizontal layers the soil element will be restrained against lateral deformation as it is acted by a lateral force. It is important to note that the tensile force in the reinforcing element depends on there being lateral strain.
All reinforced soil structures are combinations of suitable earth fill usually with several layers of the reinforcing elements placed on compacted fill. The technique is used to construct:
- vertical walls and abutments
- slopes of embankments steeper than would be stable (or at an acceptable degree of stability) with unreinforced soil
- embankments on soft soils, where the foundation soil has inadequate bearing capacity to support the height of fill
- unpaved roads
- special mattress-type foundations or stress-reducers for soft or backfilled ground
- Repairs to slipped material of earth slopes
Advantages of reinforced soil
- Smaller quantities of earth fill are needed
- Steeper embankment slopes reduce the land take required
- Construction can be directly done on soft ground
- The technique is not a separate operation in the construction process, but is a part of the placing and compaction of the earth fill. Hence structures can often be built more quickly than by conventional methods.
Limitations of reinforced soil
Reinforced soil relies upon deformation for its effectiveness, which means the soil strain has to be transferred to the reinforcement for it to develop its tensile or bearing resistance. There are some concerns about the durability and long time performance of the reinforcing material. Severe and rapid corrosion of steel reinforcement is possible.
Polymeric materials degrade when exposed to ultra-violet rays and can be damaged by rough handling on site or by sharp stones in fill. When constructing on soft soils care has to be taken not to overstress the reinforcement.