GROUND IMPROVEMENT

NPTEL Course

Prof. G L Sivakumar BabuDepartment of Civil EngineeringIndian Institute of ScienceBangalore 560012Email: gls@civil.iisc.ernet.in

Lecture 3

Module I

Need for Ground Improvement Classification of ground modification

techniques Emerging trends in ground Improvement

Recap:Classification of Ground Improvement techniquesMethods and techniques of Ground ImprovementFactors affecting the selection of techniques

Need for Soil Improvement

Soft Clay Liquefaction and sinkhole formation

Methods for Soil ImprovementGround

ReinforcementGround

ImprovementGround

Treatment

• Stone Columns• Soil Nails• Micropiles• Jet Grouting• Ground Anchors• Geosynthetics• Fibers • Lime Columns• Vibro-Concrete

Column• Mechanically

Stabilized Earth• Biotechnical

• Surface Compaction

• Drainage/Surcharge• Electro-osmosis• Compaction

grouting• Blasting• Dynamic

Compaction

• Soil Cement• Lime Admixtures• Flyash• Dewatering• Heating/Freezing• Vitrification

Benefits/Objectives of ground improvement techniques

Increase of strength Reduce distortion under stress (Increases

stress-strain modulus) Reduce compressibility (volume decreases

due to a reduction in air voids or water content under loads)

Continued :

Prevent detrimental physical or chemical changes due to environmental conditions (freezing / thawing, wetting / drying)

Reduce susceptibility to liquefaction Reduce natural variability of borrow

materials and foundation soils

Jet grouted soilcretecolumns

Stone columns

Nailing and Reinforced soil

Geosynthetic products

Fibers and reinforced earth

Effect of fibers on strength response

0

200

400

600

800

1000

1200

1400

0 5 10 15 20 25Strain(%)

Dev

iato

r stre

ss(k

Pa)

0%0.50%1.00%1.25%1.50%2.00%2.50%

Red soilfl =15 mmfd = 0.25mmσ3 =50 kPa

Effect of fibers on compressibility

0.3

0.4

0.5

0.6

0.7

1 10 100 1000log p(kPa)

void

ratio

0%0.50%1.0%1.50%2.00%2.5%

red soilfl = 10mmfd = 0.25mm

Effect of fibers on swell response

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

1 10 100 1000 10000Time (minutes)

Swel

l (%

)

0%0.50%1.00%1.50%

Black cotton soilfl =15mmfd = 0.25mm

Effect of fibers on piping resistance

0.00

0.05

0.10

0.15

0.20

0.25

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5Hydraulic gradient

Seep

age

velo

city

(cm

/sec

)

0%0.25%0.50%0.75%1.00%

Red soilfl = 50 mm

Trends Today

Environmental Geotechnics and solid waste management using ground improvement techniques

Containment and constructive use of waste materials

Low-cost technologies with soil and additives

Geosynthetics Biotechnical stabilization

Catalysts and accelerators

Development of new machinery, particularly for deep compaction

Availability of new construction materials such as geofoams, geocomposites

Emergence of better guidelines for determining the suitability of specific techniques for certain types of soils and site conditions.

Better understanding of the geotechnical processes involved and appreciation of the significance of the construction sequence.

Refinement of methods of analysis and computer modeling techniques

Likely Trends Tomorrow Microbes to stabilize or remediate soils, Nanotechnology to modify the behavior of clay, Nano-sensors and MEMS to characterize and

monitor the behavior of geomaterials and geosystems,

Remote sensing and noninvasive ground-based sensing techniques, and

Next-generation geologic data models to bridge sensing, computation, and real-time simulation of behavior for adaptive management purposes and geophysics for urban infrastructure detection.