This document discusses various ground improvement techniques including vibro-flotation, stone columns, micro piles, soil nailing, and grouting. It explains that these techniques are needed to construct structures in unfavorable geotechnical conditions like filled, low-lying, or waste lands by increasing soil strength and reducing compressibility, permeability, and liquefaction potential. Specific techniques are then described in more detail, including field compaction, dynamic compaction, vibro-compaction, vibroflotation, and stone columns.

1. Unit 2: Ground improvement techniques
Department of Civil Engineering, PCCOE, Pune – 411 044 1
Syllabus
Unit 2: Ground improvement techniques
Ground improvement techniques such as- vibro-flotation, stone
column, micro pile, soil nailing, grouting techniques in soft and hard
strata, dewatering techniques such as single and double point system .

2. Most of the times soil properties not known .
 With increasing demand of urbanization we need to construct structure in unfavorable
geotechnical conditions. (Filled up sites, Low lying water logged, Waste lands)
Type of geo material and its probable problems are as follows-
Need of Ground Improvement technique
2

3. Type of geo material and its probable problems are as follows-
Need of Ground Improvement technique
3

4. Geotechnical problem and possible causes-
Need of Ground Improvement technique
4

5. Objectives of Ground Improvement technique
Need of Ground Improvement technique
5
(1)To increase the strength(bearing capacity, shear strength etc)
(2) To control deformations and accelerate consolidation
(3) To provide lateral stability , Reduce erodability
(4) To form seepage cut-off , Control Permeability
(5) To increase resistance to liquefaction
(6) Reduce compressibility

6. Methods of Ground Improvement
6

7. Methods of Ground Improvement –
field compaction
 Least expensive method and simplest method to increase density, strength,stiffness and reduce
permeability. It improving mechanical properties of soil by densify the particles using compactive
effort .
 Traditional compaction by roller suitable for 0.3m compaction
 High energy impact roller suitable for granular material upto 0.6m deep
 Involves Soil strength and density will be maximum when compacted at optimum moisture
content
 Applicable to both cohesive as well as non-cohesive soils
 Cohesive soils-silt and clay: Traditional compaction, Kneading tamping and impact
 Cohesionless soils- sands and gravels or granular course grain material: Intelligent compaction
or vibration

8. Methods of Ground Improvement –
Dynamic compaction
 Suitable for granular material, near-surface soil is poor , collapsible soil and waste
material with fine upto 10m.
 Suitable for both cohesive and cohesionless soils
 Drop a very heavy weight (6 to170 Tons) onto the soil from a relatively great height (10
to 40m) to apply high energy on ground surface causing liquefaction of saturated material
and densification of unsaturated material.

9. Methods of Ground Improvement –
Dynamic compaction
 Degree of densification achieved is a function of the energy input (weight and drop height)
as well as the saturation level, fines content and permeability of the material
 Done systematically in a rectangular or triangular pattern in phases.
 Spacing between impact points depend upon:
 • Depth of compressible layer
 • Permeability of soil
 • Location of ground water level
 Deeper layers are compacted at wider grid spacing
 Upper layer are compacted with closer grid spacing

10. Methods of Ground Improvement –
Densification by Vibro-Compaction- Vibroflotation
 Apply vibratory forces and or water by a probe on surrounding problematic geo material
causing liquefaction and densification.
 This method increases density, strength and reduce deformation, liquifaction,collapsible
potential to greater depth say 15m. Loose sand is densified to create stable foundation soils.
Mainly for cohesionless soils
 They are suitable for clean sands where no clay or less than 15% silt available.
 The action of the vibrator, usually accompanied by water jetting, reduces the inter-granular
forces between the soil particles, allowing them to move into a denser configuration, typically
achieving a relative density of 70 to 85 percent. Compaction is achieved above and below the
water table.

11. 11
Methods of Ground Improvement –
Densification by Vibro-Compaction-
Vibroflotation

12. Methods of Ground Improvement –
Densification by Vibro-Compaction-
Vibroflotation
12

13. Methods of Ground Improvement –
Stone Column
 Also known as vibro-replacement or vibro-displacement, is
a ground improvement process where vertical columns of
sand or compacted aggregate are formed through the soils to
be improved. They are suitable for 5m-15m effective depth.
 The vibrator first penetrates to the required depth by
vibration and air or water jetting or by vibration alone.
 Gravel is then added at the tip of the vibrator and
progressive raising and re-penetration of the vibrator results
in the gravel being pushed into the surrounding soil.
 Increase bearing capacity, stability, stiffness, reduces
settlement and liquefaction and increase consolidation
Densification- Increase shear strength & Bearing Capacity
13

14. Stone Column
Vibration Methods- Vibrofloatation / Vibrocomposer
• Vibrofloat- assisted with water jet or compressed air
• Backfill gravel- 12mm-75mm
• More effective but costly
14

15. Rammed Stone Column
• Uses a bored piling rig to dig the borehole and
granular fill is placed and compacted in stages
• Cased borehole is prepared
• Granular material (2-75mm ) filled upto 2-3m
depth from surface
• Each layer compacted using rammer of 15-20kN
from height about 1.5m
• Casing is withdrawn in stages
15