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Soil improvement in its broadest sense is the alteration of any property of a soil to improve its engineering performance such as strength, reduced compressibility, reduced permeability, or improved ground water condition. This may be either a temporary process to permit the construction of a facility or may be a permanent measure to improve the performance of the completed facility. We will discuss about the details of soil improvement.Contents:
Techniques of Soil Improvement
There are various techniques used for the improvement of the soil based on the construction activity and type of soil. The soil improvement techniques are,- Surface Compaction
- Drainage Methods
- Vibration Methods
- Precompression and consolidation
- Grouting and Injection
- Chemical Stabilisation
- Soil Reinforcement
- Geo textiles and Geo membranes
- Other Methods
1. Surface Compaction
One of the oldest methods of soil densification is surface compaction. Construction of a new road, a runway, an embankment or any soft or loose site needs a compacted base for laying the structure. If the depth to be densified is less, the surface compaction alone can solve the problem. The usual surface compaction devices are rollers, tampers and rammers. All conventional rollers like smooth wheel, rubber-tyred, sheep foot, vibratory and grid rollers can be used.
Fig 1: Plate Compactor
Fig 2 : Jack Jumping Rammer
2. Drainage Methods
Ground water is one of the most difficult problems in excavation work. The presence of water increases the pore water pressure and decreases the shear strength. Further heavy inflow of water to the excavations is liable to cause erosion or collapse of the sides of open excavations. Certain methods are available to control the ground water and ensure a safe and economical construction scheme.
Fig 3: Vacuum Dewatering system
3. Vibration Methods
Vibration methods can be effectively used for rapid densification of saturated non-cohesive soils. Vibrations and shock waves in loose deposits of such materials cause liquefaction followed by densification accompanying the dissipation of excess pore water pressures. Some of the mostly adopted vibration methods are blasting, Vibrating probe, Vibratory rollers, Vibro-displacement Compaction Piles, Vibrofloatation, Heavy Tamping etc.
Fig 4: Vibroflotation
4. Pre-Compression and Consolidation
This method aims to consolidate the soil before construction. Various techniques adopted are Preloading and Surcharge Fills, Vertical Drains, Dynamic Consolidation, Electro osmotic Consolidation etc.
Fig 5: Dynamic Consolidation
5. Grouting and Injection
Grouting is a process whereby stabilizers, either in the form of suspension or solution are injected into subsurface soil or rock for one or more of the following applications:- Control of ground water during construction
- Void filling to prevent excessive settlement
- Strengthening adjacent foundation soils to protect them against damage during excavation, Pile driving, etc.
- Soil Strengthening to reduce lateral support requirements
- Stabilization of loose sands against Liquefaction
- Foundation Underpinning
- Reduction of machine foundation vibrations
Fig 6: Soil Grouting
6. Chemical Stabilization
Chemical Stabilization has been widely used in the form of lime, cement, fly ash and the combination of the above is widely used in soil stabilization. Chemical Stabilizations reduce permeability of the soils, improve shear strength, increase bearing capacity, decrease settlement and expedite construction. Chemical Stabilization is used for surface soils more successfully. Mixtures of soils and chemicals are mixed either mechanically in place or by batch process. Some of the chemicals used are Lime, Cement, and Fly Ash etc.7. Soil Reinforcement
Soil Reinforcement is in the form of a weak soil reinforced by high-strength thin horizontal membranes. A large variety of materials such as rubber, aluminum and thermoplastics have been used successfully.
Fig 7: Fiber Reinforcement
8. Geotextiles and Geomembranes
Geotextiles are porous fabrics manufactured from synthetic materials, which are primarily petroleum products and others, such as polyester, polyethylene, polypropylene and polyvinyl chloride, nylon, fibreglass and various mixtures of these. Geotextiles are used as separators, filters, Drains, reinforcement, geomembranes etc.
Fig 8: GeoCells
Fig 9: Geo Textile
