GROUND IMPROVEMENT TECHNIQUES

Need for Ground Improvement

1) Abandoning the site and locate the structure elsewhere.

2) Designing deep foundation to carry the weight of the structure.

3) Redesigning the structure according to the ground conditions.

Improve the properties of the ground prior to construction.

WHAT IS GROUND IMPROVEMENT?

Ground Improvement is the modification of the ground properties in order to achieve the required ground conditions for the particular use of ground.

The areas of usage include a broad construction spectrum from industrial, commercial and housing projects to construction of dams, tunnels, ports, roadways and embankments. These techniques can be used for varied types of soils ranging from coarse grained to fine grained.

GROUND IMPROVEMENT TECHNIQUES

Help

• to reduce permeability• to reduce compressibility• to increase shear strength• to increase bearing capacity

Methods of soil improvement

• Vibro-Compaction• Grouting• Vertical Drain• Dynamic Compaction• Stabilisation using Admixtures

VIBRO COMPACTION• Vibro compaction densifies clean, cohesion less granular soils by

means of a down hole vibrator which is typically suspended from a crane and lowered vertically into the soil under its own weight.

• Penetration is usually aided by water jets integrated into the vibrator assembly. After reaching the bottom of the treatment zone, the soils are densified in lifts as t he probe is extracted.

• • During vibro compaction , clean sand backfill is typically added at

the ground surface to compensate for the reduction in soil volume resulting from the densification process.

• • The vibratory energy reduces the inter-granular forces between

the soil particles, allowing them to move into a denser configuration, typically achieving a relative density of 70 t o 85 percent . The treated soils have increased density, friction angle and stiffness.

GROUTING

Defined as the injection of a special liquid or slurry material called ‘grout’ into the ground for the purpose of improving the soil or rock.

Types of grouts:

a) Cement Grouts

b) Chemical Grouts

Grouting Methods

Intrusion grouting• Consists of filling joints or fractures with

grout.• Helps in reduction of hydraulic

conductivity.• Used to prepare foundation and

abutments for dams.• Done using cement grouts.

Permeation grouting• Injection of thin grouts into the soil.• Once the soil cures, becomes a solid

mass.• Done using chemical grouts.• Used for creating groundwater barriers

or preparing ground before tunneling.

Grouting Methods

• Compaction grouting• When low-slump compaction grout is

injected into granular soils, grout bulbs are formed that displace and densify the surrounding loose soils.

• Used to repair structures that have excessive settlement

• Jet grouting• Uses a special pipe with horizontal jets

that inject grout into the ground at high pressures.

• Commonly used for ground water control projects.

• Suitable for stabilizing soils before excavation or tunneling.

DYNAMIC COMPACTION

• Uses a special crane to lift 2-50 tons to heights of 7m-35m and then drop these weights onto the ground.

• Cost effective method of densifying loose sands and silty soils up to 15 to 30 feet deep.

• Good densification occurs up to a depth of 5m-10m.

VERTICAL DRAINS

• Vertical drains are installed under a surcharge load to accelerate the drainage of impervious soils and thus speed up consolidation.

• These drains provide a shorter path for the water to flow through to get away from the soil.

• Time to drain clay layers can be reduced from years to a couple of months.

• Consolidation takes place in only one direction .

• Vertical drainage path may be substantially longer.

• It may take more than 10 years to consolidate.

• Pore water will flow laterally.• Pore water pressure dissipates as

the layer drains and water is conveyed through vertical drains.

• It takes only about 6 months to consolidate.

INSTALLATION

ADVANTAGES OF VERTICAL DRAINS

• Minimum disturbance to soil layer during installation.

• High water discharge capacity.

• High tensile strength prevents the collapse of flow path.

• Fast and easy installation up to 40 m.

Stabilization Using Admixtures

• Most common admixture is Portland Cement.

• When mixed with soil, forms soil-cement which is comparable to a weak concrete.

• Other admixtures include lime and asphalt.

• Objective is to provide artificial cementation, thus increasing strength and reducing both compressibility and hydraulic conductivity.

• Used to reduce expansion potential of clays.

• Used in surface mixing applications.

CONCLUSION

• Ground improvement is a rapidly developing field as suitable sites for construction are not available these days.

• Its applicability has been proven in the recent past for a wide range of structures such as roads, runways, ports, power plants, railways, dams & other infrastructure facilities .

• These techniques have been used all over the world for a wide range of soils starting from loose sands, silts, marine clays to weak rocks.

• Based on the soil conditions, loading intensity and intended performance, an appropriate ground improvement technique can be designed to attain the desired performance.

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