Lecture 3
NPTEL Course
GROUND IMPROVEMENT Prof. G L Sivakumar Babu Department of Civil Engineering Indian Institute of Science Bangalore 560012 Email:
[email protected]
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 Red soil f l =15 mm f d = 0.25mm σ3 =50 kPa
1200 1000
0% 0.50% 1.00% 1.25% 1.50% 2.00% 2.50%
) a P k ( 800 s s e r t s r 600 o t a i v e 400 D
200 0 0
5
10
Strain(%)
15
20
25
Effect of fibers on compressibility 0.7 red soil f l = 10mm f d = 0.25mm
0% 0.50% 1.0% 1.50% 2.00% 2.5%
0.6
o i t a r 0.5 d i o v
0.4
0.3 1
10
log p(kPa)
100
1000
Effect of fibers on swell response 7.0 0% 0.50% 1.00% 1.50%
Black cotton soil f l =15mm f d = 0.25mm
6.0 5.0 ) 4.0 % ( l l e w S3.0
2.0 1.0 0.0 1
10
100 Time (minutes)
1000
10000
Effect of fibers on piping resistance 0.25 Red soil f l = 50 mm ) 0.20 c e s / m c ( 0.15 y t i c o l e v e 0.10 g a p e e S
0% 0.25% 0.50% 0.75% 1.00%
0.05
0.00 0.0
0.5
1.0
1.5 2.0 Hydraulic gradient
2.5
3.0
3.5
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.
