2. ALTERNATIVES FOR INADEQUATE GROUND?
Abandon the site and locate the structure
elsewhere
Design deep foundations to carry the weight of
the structure to competent stratum
Redesign the structure according to the ground
conditions
Improve the properties of the ground prior to
construction
3. BASIC PRINCIPLE OF GROUND IMPROVEMENT
Ground improvement is the modification of
the ground properties in order to achieve the
required ground conditions for the particular use
of the ground.
Densification of the ground , E.g.: Compaction
Accelerate the consolidation, E.g.: Vertical drains
Usage of geo synthetics, E.g.: Geotextiles
Usage of admixtures, E.g.: Cement stabilization
Preloading
Mechanical Stabilization
5. STONE COLUMN TECHNOLOGY
It is also known as Vibro replacement or Vibro
displacement
Compacted aggregates form as a vertical
columns to improve the soil conditions.
Resulting in considerable increase in vertical
load capacity and to an extent contribute to as
drains to dissipate pore water pressure.
7. STONE COLUMN : WET / TOP FEED METHOD
Vibro Probe
Step 1 : Penetration of probe
Step 2 : Backfilling of aggregate and compacting
Step 3 : Consolidation of granular fill and
finishing the column
8. STONE COLUMN : DRY / BOTTOM FEED METHOD
Step 1 : Penetration of probe
Step 2 : Installation of aggregate through separate duct
along the vibro probe
Step 3 : Consolidation of granular fill and finishing the
column
9. STONE COLUMN : ADVANTAGES
Technically and potentially economical
alternative for deep compaction.
Alternative for dynamic compaction, deep
blasting etc.,
Quicker than preloading the site
It increases the bearing capacity, reduces the
settlements, liquefaction potential.
10.
11. CASE STUDY:
Four Lane National Highway Connectivity to ICTT –
Vallarpadam, Kochi
Connects NH - 47 and NH - 17.
Project cost was revised from 329.46 cr to 571.20 cr due
to ground improvement, bridges and retaining walls.
Road Length – 17.2km, total length of bridges – 2.93km.
Ground improvement works – 10km.
Wet /Top method of installation was used.
Stone columns where installed in 15 locations between
Ch, 0.245 and 16.210
14. CASE STUDY :STONE COLUMN
Quantity of stone aggregate used : 28,774 cum.
Geo grid consumed: 35,536. 12 sq.m
Bulk density considered : 1.8 MT/m3
App. Quantity of aggregate for one column : 35MT
Total number of stone columns : 22,166 no's
Time required for each stone column : 60 min
No. of stone columns installed per day : 15 no's
Total running meter of all the columns : 91,641 Rm
16. BAND DRAIN TECHNOLOGY - PVD
Used in loose, compressible and water
saturated clay and silty clays.
Soils are characterized by very loose skeleton
and a large pore sizes filled with water
Requires about ten or more years to
consolidate on preload.
PVD – Prefabricated Vertical Drain.
17. WHAT IS VERTICAL DRAIN?
Consolidation takes place in only
one direction
Vertical drainage path may be
substantially longer
It may take 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 6months or so
to consolidate
18. COMPONENTS OF PVD?
Core
Core : It is called drained body
corrugated, flexible and made of
polypropylene, designed to provide
high discharge capacity, high tensile
and compressive strength.
Filter Jacket: Non – woven ,thermically
Filter
bonded polypropylene wrapped
around the core. Acts as the filter to
allow ground water to the core.
19. ADVANTAGES OF BAND DRAIN TECHNOLOGY:
Minimum disturbance to the soil layers during
installation
High water discharge capacity
High tensile strength prevents the collapse of
flow path.
Fast and easy installation
Deep installation up to 40m.
20. CASE STUDY:
Four Lane National Highway Connectivity to ICTT –
Vallarpadam, Kochi
Connects NH- 47 and NH – 17.
Project cost was revised from 329.46 cr to 571.20 cr due
to ground improvement, bridges and retaining walls.
Road Length – 17.2km, total length of bridges – 2.93km.
Ground improvement works – 10km.
PVD were installed in 8 locations between Chainage 8.400
– 15.000
24. CASE STUDY: BAND DRAIN TECHNOLOGY
Total length of band drains : 56,21,780 Rm
Total Granular blanket : 1,23,386 Cum
Total Geotextiles used : 3,90,714 sq.m
Time taken for install one band drain of 25m : 1min
Time taken for splicing the wick : 1 min
25. CASE STUDY: BAND DRAIN TECHNOLOGY
After the installation of band
drains, Casagrande peizometer and plate type
settlement recorders where installed in order to
check the settlements
26. CASE STUDY: BAND DRAIN TECHNOLOGY
Description Values
Cumulative Heights Stage 1 : 3.0m ( i.e., 1.0m above the top of
reclamation)
Stage 2 : 5.5m ( includes 1.5m of
additional surcharge)
Waiting period of each stage Stage 1 : 6.0 months
Stage 2 : 6.0 months
The water coming out of the vertical drains is collected
in temporary ditch. The water collected is regularly
dewatered to the adjoining area.