The ground can be improved by adapting certain ground improvement techniques. Vibro-compaction increases the density of the soil by using powerful depth vibrators. Vacuum consolidation is used for improving soft soils by using a vacuum pump.
Preloading method is used to remove pore water over time. Heating is used to form a crystalline or glass product by electric current. Ground freezing converts pore water to ice to increase their combined strength and make them impervious. Vibro-replacement stone columns improve the bearing capacity of soil whereas Vibro displacement method displaces the soil. Electro osmosis makes water flow through fine grained soils.
Electro kinetic stabilization is the application of electro osmosis. Reinforced soil steel is used for retaining structures, sloping walls, dams etc. seismic loading is suited for construction in seismically active regions. Mechanically stabilized earth structures create a reinforced soil mass.
The geo methods like Geosynthetics, Geogrid etc. are discussed. Soil nailing increases the shear strength of the in-situ soil and restrains its displacement. Micro pile gives the structural support and used for repair/replacement of existing foundations.
Grouting is injection of pumpable materials to increase its rigidity. The jet grouting is quite advanced in speed as well as techniques when compared with the general grouting.
- Latest Ground Improvement Techniques
- Vibro-Compaction Method of Ground Improvement
- Vacuum Consolidation of Soil for Ground Improvement
- Preloading or Pre-Compression of Soil for Ground Improvement
- Thermal Stabilization of Soil for Ground Improvement
- Ground Freezing Technique for Ground Improvement
- Vibro-Replacement Stone Columns for Ground Improvement
- Mechanically Stabilized Earth Structures
- Soil Nailing Technique for Ground Improvement
- Micropiles for Ground Improvement
- General Grouting for Ground Improvement
- Grouting Techniques
- Jet Grouting Technique for Ground Improvement
Latest Ground Improvement TechniquesFollowing are the recent methods of ground improvement Techniques used for stabilization of soil:
- Vibro Compaction
- Vacuum Consolidation
- Preloading of soil
- Soil stabilization by heating or vitrification
- Ground freezing
- Vibro-replacement stone columns
- Mechanically stabilized earth structures
- Soil nailing
Vibro-Compaction Method of Ground Improvement
Advantages of Vibro Compaction Method:
- Reduction of foundation settlements.
- Reduction of risk of liquefaction due to seismic activity.
- Permit construction on granular fills.
Vacuum Consolidation of Soil for Ground Improvement
Applications of Vacuum Consolidation of Soil:
- Replace standard preloading techniques eliminating the risk of failure.
- Combine with a water preloading in scare fill area. The method is used to build large developments on thick compressible soil.
- Combine with embankment pre-load using the increased stability
Preloading or Pre-Compression of Soil for Ground ImprovementPreloading has been used for many years without change in the method or application to improve soil properties. Preloading or pre-compression is the process of placing additional vertical stress on a compressible soil to remove pore water over time. The pore water dissipation reduces the total volume causing settlement. Surcharging is an economical method for ground improvement. However, the consolidation of the soils is time dependent, delaying construction projects making it a non-feasible alternative.
Applications of Preloading of Soil
- Reduce post-construction
- Reduce secondary compression.
- Improve bearing capacity
- Immobilization of radioactive or contaminated soil
- Densification and stabilization
Ground Freezing Technique for Ground Improvement
Applications of Ground Freezing Technique
- Temporary underpinning
- Temporary support for an excavation
- Prevention of groundwater flow into excavated area
- Temporary slope stabilization
- Temporary containment of toxic/hazardous waste contamination
Vibro-Replacement Stone Columns for Ground Improvement
Principles of Vibro-Replacement TechniqueThe stone columns and intervening soil form and integrated foundation support system having low compressibility and improved load bearing capacity. In cohesive soils, excess pore water pressure is readily dissipated by the stone columns and for this reason, reduced settlements occur at a faster rate than is normally the case with cohesive soils. There are different types of installation methods which can be broadly classified in the following manner:
- Wet top feed method
- Dry bottom feed method
- Offshore bottom feed method
Summary of Vibro Replacement Method
|Land / offshore application||
Applications of Vibro-Replacement for Ground Improvement:
- Reduction of foundation settlement
- Improve bearing capacity/reduce footing size requirements
- Reduction of the risk of liquefaction due to seismic activity
- Slope stabilization
- Permit construction on fills
- Permit shallow footing construction
|Clays||Marginal to good|
|Minespoils||Excellent (depending on gradation)|
Mechanically Stabilized Earth Structures
Principles of Mechanically Stabilized Earth Structures:
- The reinforcement is placed in horizontal layers between successive layers of granular soil backfill. Each layer of backfill consists of one or more compacted lifts.
- A free draining, non plastic backfill soil is required to ensure adequate performance of the wall system.
- For walls reinforced with metallic strips, load is transferred from the backfill soil to the strip reinforcement by shear along the interface.
- For walls with ribbed strips, bar mats, or grid reinforcement, load is similarly transferred but an additional component of strength is obtained through the passive resistance on the transverse members of the reinforcement.
- Facing panels are typically square, rectangular, hexagonal or cruciform in shape and are up to 4.5m ^2 in area.
- MSEW- Mechanically Stabilized Earth Walls, when the face batter is generally steeper than 70 degrees.
- RSS- Reinforced Soil Slopes, when the face batter is shallower.
- RSS structures are cost effective alternatives for new construction where the cost of embankment fill, right-of-way, and other consideration may make a steeper slope desirable.
- Another use of reinforcement in engineered slopes is to improve compaction at the edges of a slope to decrease the tendency for surface sloughing.
- Stabilization of railroad and highway cut slopes
- Excavation retaining structures in urban areas for high-rise building and underground facilities
- Tunnel portals in steep and unstable stratified slopes
- Construction and retrofitting of bridge abutments with complex boundaries involving wall support under piled foundations
Micropiles for Ground ImprovementMicropiles are small diameter piles (up to 300 mm), with the capability of sustaining high loads (compressive loads of over 5000 KN).The drilling equipment and methods allows micropiles to be drilled through virtually every ground conditions, natural and artificial, with minimal vibration, disturbances and noise, at any angle below horizontal. The equipment can be further adapted to operate in locations with low headroom and severely restricted access.
Applications of Micropiles for Ground Improvement
- For Structural Support and stability
- Foundation for new structures
- Repair / Replacement of existing foundations
- Arresting / Prevention of movement
- Embankment, slope and landslide stabilization
- Soil strengthening and protection
Example of Micro Piles for Ground Improvement:In India, in some circumstances steel pipes, coated wooden piles are used as cost-effective Options in improving the bearing capacity of foundation or restrict Displacements to tolerable levels and similar uses in stabilization of slopes, strengthening of foundations are common. Sridharan and Murthy (1993) described a Case study in which a ten-storeyed building, originally in a precarious condition due To differential settlement, was restored to safety using micropiles. Galvanized steel Pipes of 100 mm diameter and 10 m long with bottom end closed with shoe, driven at An angle of 60o with the horizontal were used and the friction between the pile and the soil was used as the design basis in evolving the remedial measures.
General Grouting for Ground ImprovementGrouting is the injection of pumpable materials into a soil or rock formation to change the physical characteristics of the formation. Grouting selection considerations are Site specific requirement, Soil type, Soil groutability, Porosity. Grouting can be prevented by Collapse of granular soils, Settlement under adjacent foundations, Utilities damage, Day lighting. Grouting can provide Increased soil strength and rigidity, reduced ground movement, Predictable degree of improvement. Steps for General Grouting Technique for Soil Stabilization
- Identify underground construction problem.
- Establish objectives of grouting program.
- Perform special geotechnical study.
- Develop initial grouting program.
- Develop performance prediction.
- Compare with other solutions.
- Refine design and prepare specifications.
Grouting TechniquesThe various injection grouting techniques used by grouting contractors for ground improvement / ground modification can be summarized as follows:
- Compaction Grouting
- Jet Grouting