Uses of newer Techniques to sustain the load and improvising the solution to next level.

1. PRE-FABRICATED VERTICAL
DRAIN AND STONE COLUMNS
Prepared by- Bhadani Ravi (14CL004)

2. WHAT IS THE REQUIREMENT OF
GROUND IMPROVEMENT?
 To alter the natural properties of rock or soil
 Reducing compressibility and permeability
 Increasing strength ,bearing capacity

3. What is PVD ?

4. What is PVD ?
 Prefabricated Vertical Drain - PVD
 Typically 95 -100 mm wide by 3 - 5 mm thick
 Synthetic core wrapped with geotextiles.
 Many types of core.

5. PVDs shorten drainage path
 90% Consolidation time reduced from >15 years to 1 year

6. Introduction to PVD
 Prefabricated vertical drain or “Wick drain” are composed of plastic
encased by geotextiles for the purpose of expediting consolidation
of slow draining soils.
 Two main components of PVD serve the following functions;
1. Core serves as a longitudinal flow path along the drain .
2. Filter jacket allows water to pass into the core while restricting
intrusion of soil particles.
 Prefabricated wick drains have several other purposes. They may
be applied to reduce potential down drag on piles, or increase
storage capacity for future landfills and waste containment sites.
 A developing application for PVD are the collection and extraction
of contaminated groundwater, which may be coupled with cutoff
walls to ensure full withdrawal.

7. Suitable soils.
 PVD are not versatile for all soil types and geological
conditions. The drains can be implemented in soils that
are moderately to highly compressible under static
loading. Applicable soils include:
1. Inorganic silts and clays of low to moderate sensitivity
2. Organic layers
3. Decomposed peat
4. Clayey and silty sands
5. Dredge spoils
6. Varved cohesive deposits

8. Installation of PVD.

9. Drain Influence Zone
 The drain influence zone (D) is a function of drain spacing (S) only.
Vertical drains are commonly installed in square or triangular
patterns. Square pattern layouts have greater ease and control in
the field. However the triangular patterns are preferred to provide
more uniform consolidation between drains.

10. Settlement Vs Time Curve

11. Benefits of PVD
 Decrease overall time required for completion of primary
consolidation due to preloading
 Decrease the amount of surcharge required to achieve the desired
amount of pre-compression in the given time
 Increase the rate of strength gain due to consolidation of soft soils
when stability is of concern
 Comparison to sand drains: Economic competitiveness, fewer
disturbances to the soil mass compared to displacement sand
drains, and the speed and simplicity of installation. Also feasible to
be installed in a non vertical orientation.
 Installation of PVD typically 6000 linear meter per day and result in
a lower project cost.
 No risk of PVDs breaking during installation.- sand drain have
discontinuous if mandrill is too fast.
 No shear failure of PVDs during settlement.

12. Stone Columns

13. What is Stone Columns ?
 A ground improvement technique to improve the load
bearing capacity and reduce the settlement of the
soil
 Stone column consists of crushed coarse aggregates of
various sizes.
 The stone columns serve two basic functions, namely
1. Providing strength reinforcement to the soil and
2. Acting as vertical drains to allow subsoil consolidation
to occur quickly under any given loading.
 Stone columns are constructed by experienced
contractors using specialist equipment. The
construction uses an excavator with a vibrating probe
to feed stone into the ground, forming a vertical column
of stone

14. Functions of Stone Columns
 Improve the bearing capacity of weak soil.
 Carry high shear stress by acting as stiff elements and hence increase the
stability of embankment founded on soft ground.
 Facilitate radial drainage (by acting as vertical drains) and dissipate rapidly
the excess pore water pressure leading to acceleration of consolidation
process and reduced post-construction settlements.

15. Suitable soils.
 Soft, Non-compactable, Weak soil
 Granular with high fines content
 Organic soils
 Marine/ Alluvial clays
 Liquefiable soils
 Cohesive soils

16. Rammed Stone Column
Method

17. Vibro-Replacement Method

18. Basic Design Parameters
 Stone column diameter, D
 Depth of stone column.
 Pattern.
 Spacing.
 Equivalent diameter.
 Replacement ratio.

19. Advantages of Stone Columns.
 Increase the bearing capacity of in-situ soils
 To reduced total and differential settlements
 Expedites consolidation settlement.
 Mitigates the risk of liquefaction.
 More economical than piling.
 No waiting period after installation.
 Homogenizes variable soil properties