1.1 Introduction
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.