Foundation soil improvement:

• Process of improving engineering properties of soil to make more stable foundation.
• Reduce permeability and compressibility of soil.
• Increase shear strength of soil.
• Increase bearing capacity of foundation of soil.

Method of soil improvement:

• Mechanical compaction
• Dynamic compaction
• Soil stabilization by use of admixture
• Sand compaction piles
• Soil stabilization by injection of suitable grout

1.2 Mechanical compaction

• It is the process of increasing density of soil by application of mechanical energy.
• For cohesive soil compaction is done till optimum moisture content.
• For cohesion less soil compaction is done by vibrating.

Purpose:

• Increase shear strength.
• Reduce compressibility.
• Reduce permeability.

Equipment:

1. Smooth wheeled roller

2. Vibratory roller

3. Impact rammer

1.3 Preloading

• Soil improvement by applying compressive load to reduce settlement and increase bearing capacity.
• It is also known as tempory loading.

1.4 Sand compaction pile and stone column

Sand compaction pile:

• This method is used for improving ground stability, preventing liquefaction and reducing settlement.
• Process: By installing sand into soft ground by casting pipe and vibrating the sand to produce firmly compacted sand piles in the ground.

Stone column:

• This method is used for installing and compacting pile to reduce liquefaction.
• Size of stone are 6 mm to 40 mm.

1.5 Soil stabilization by the use of admixture

• Physical properties of soil can be improved economically by use of admixture like lime, portland cement and asphalt.
• Applicable only in shallow foundation.

Types of admixture:

1. Soil cement admixture

• Mixture of cement and water with soil and compacted to high density.
• PPC cement is used.
• Used in sub base and base course on road.

2. Soil lime stabilization

• Improves strength, stiffness and density.
• Reduce plasticity index.
• Used in canal lining.

1.6 Soil stabilization by injection of suitable grout

• It is the process by which fluid like material either in suspension or in solution is injected in void space of underground soil or rock.

Effective in following case:

• When foundation has to be constructed below ground water table.
• Difficult for access of foundation level.
• Geometric dimension of foundation is complicated.

Types of soil stabilization by injection of suitable grout:

• Chemical grouting ( silica and resins)
• Cement grouting

References:

• Terzaghi, Karl, Peck, R.B & John, Wiley (1969) Soil mechanics in engineering practice, New York.
• Arora , K.R (2008), Soil mechanics and foundation engineering, Delhi: Standard Publisher Distribution.

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