Lecture

Lecture 3

NPTEL Course

GROUND IMPROVEMENT
Prof. G L Sivakumar Babu Department of Civil Engineering Indian Institute of Science Bangalore 560012 Email: [e-mail]

Module I



Need for Ground Improvement Classification of ground modification techniques



Emerging trends in ground Improvement

Recap: Classification of Ground Improvement techniques Methods and techniques of Ground Improvement Factors affecting the selection of techniques

Need for Soil Improvement

Soft Clay

Liquefaction and sinkhole formation

Methods for Soil Improvement
Ground Reinforcement • Stone Columns • Soil Nails • Micropiles • Jet Grouting • Ground Anchors • Geosynthetics • Fibers • Lime Columns • Vibro-Concrete Column • Mechanically Stabilized Earth • Biotechnical Ground Improvement Ground Treatment

• Surface • Soil Cement Compaction • Lime Admixtures • Drainage/Surcharge • Flyash • Electro-osmosis • Dewatering • Compaction • Heating/Freezing grouting • Vitrification • Blasting • Dynamic Compaction

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 soilcrete columns

Stone columns

Nailing and Reinforced soil

Geosynthetic products

Fibers and reinforced earth

Effect of fibers on strength response
1400 1200 1000 D eviator stress(kPa) 800 600 400 200 0 0 5 10 Strain(%) 15 20 25 Red soil fl =15 mm fd = 0.25mm σ3 =50 kPa 0% 0.50% 1.00% 1.25% 1.50% 2.00% 2.50%

Effect of fibers on compressibility
0.7
red soil fl = 10mm fd = 0.25mm

0.6

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

void ratio

0.5

0.4

0.3 1 10 log p(kPa)