Prefabricated Vertical Drains: L.D College of Engineering Ahmedabad

L.
D COLLEGE OF ENGINEERING AHMEDABAD

APPLIED MECHANICS DEPARTMENT
GEOTECHNICAL ENGINEERING SECTION
PRESENTATION ON
Prefabricated Vertical
Drains
GIT (3714310)
Presented by;- Sparsh K. Shukal (210280743004)
Guide:- Prof. MV Shah
Preloading and vertical drains
• When highly compressible, normally consolidated clayey soil layers
lie at limited/large depths, large consolidation settlements are
expected as the result of the loads from large buildings, highway
embankments, or earth dams etc. Pre-compression and provision
of vertical drains in soft soil may be used to minimize post
construction settlement.
• Techniques:-
• Pre-compression or Pre-loading
• Sand drains
• Pre-fabricated Vertical Drains
• Vacuum consolidation
• High Vacuum Densification Method (HVDM)
Basic Concept of Preloading:
Preloading is an economical and

effective soil improvement method that can
reduce settlement and increase the bearing
capacity of soft soil.
In other words, preloading accelerates
settlement of the soil before the
construction of the structure. Commonly, the
combination of preloading and vertical drains
is used to make the method more effective.
Code :
Prefabricated Vertical Drains IS 15284 (P
2)
• Principle: To Accelerate drainage, typically used in soft, saturated

fine-grain soils, such as silts, clays, peat, sludges, mine tailings
and dredge fills, with big pore capacity and normally filled with
water (fully saturated)
• Prefabricated Vertical Drains, also known as Wick Drains or band
drains are prefabricated geotextile filter-wrapped plastic strips
with moulded channels. These act as drainage paths to take pore
water out of soft compressible soils that consolidate faster under a
constant surcharge load.
Code of Practice: IS-15284 (Part 2)
DESIGN AND CONSTRUCTION FOR GROUND IMPROVEMENT — GUIDELINES PART 2 PRECONSOLIDATION
USING VERTICAL DRAINS
Fundamental
As stated by Terzaghi, the time taken for complete consolidation is a function

of the path travelled by the water in order to dissipate pore water pressure.
So, the basic function of PVDs is to reduce the path of water for fast
consolidation process.
Prefabricated Vertical Drains
• Wick drains or PVDs consist of a

prefabricated strip which is ideal for
water transportation. The flexible
core is typically manufactured of
polypropylene and both sides have
grooves allowing water to flow
unimpeded. The core is wrapped in a
strong and durable geotextile filter
fabric with excellent filtration
properties, allowing free access of
pore water into the drain.
• This also prevents piping of fines from
adjacent soils without clogging.
Vertical Drain Installation
Sequence
• Position Rig at Drain

Location
• Place Anchor on Drain End
• Penetrate Mandrel to
Desired Depth
• Withdraw Mandrel
• Cut Drain Material Above
Drainage Blanket
Installation Methods
1. Displacement Methods
2. Drilling Methods
3. Washing Methods
Installation of PVDs:
• Installed with approved modern equipment of type which cause
the minimal subsoil disturbance.
• To prepare working surface of installation rig. (Levelled surface)
• After site is stripped, geogrid is often placed for support.
• The drain is fed down through a hollow mandrel mounted on an
excavator or crane mast, connected at the bottom to an
expendable anchor plate. A vibratory hammer or static method is
used to insert the mandrel to design depth. It’s then removed,
leaving the wick drain in place.
• The wick drain is then cut at the ground surface, a new anchor
plate connected to it, and the mandrel moved to the next
location.
Installation of PVDs (Cont.):
Mandrel Installing
the PVDs
Setup at Site
Cutting of PVD after

installation
Installation of PVDs (Cont.):
• A pattern of installed vertical wick drains provides short drainage

paths for pore water, which accelerates the consolidation process
and the construction schedule
• On top of PVDs a drainage layer is placed to prevent it. Typically a
free draining gravel or a drainage geosynthetic.
• Drainage layer needs to be sloped so that the water will flow away
from the foundation. The slope needs to take into account any
planned settlement so that water flow is maintained throughout
the consolidation phase of the project.
Calculation of Increase in Consolidation due
to Introduction of PVDs:
Calculation of U(%): Calculation of Uz:
Calculation of Increase in Consolidation due
to Introduction of PVDs (Cont.):
Calculation of Ur:
Advantage Of Vertical Drains
1.Increased Rate Of Gain Of Shear Strength Of Clay:

• Enable the load to be applied more rapidly, thus better use of construction
plant
• In case of embankments, steeper slopes and provision of berms can be
avoided
• Lower amount of fill required
• Increased rate of consolidation
• Consequent savings in construction cost
Advantage Of Vertical Drains (Cont.)
2.Increased Rate Of Consolidation:
• Reduction in time required for primary settlement.
• Structure or embankments can put into commission and use far earlier
• Reduction in cost of maintenance
3.Stability To Embankments:
• Many soft clay strata contain thin band, or parting, of sand or silt
• Excess horizontal spread of pore pressure along these partings take place
• Vertical drains installed can relieve these excess pore pressure
Application of PVDs
• Infrastructure: The drains are for example used for the construction of
embankments for roads, railways, the preloading of runways and aprons
for airports and infilling of port areas
• Dredging and land reclamation: Drains are used when reclamations are
constructed on soft deposits
• Mining: Drains are used in Tailing ponds to accelerate consolidation or to
increase the leaching effect in use embankments
• Construction: Drains are used to make green and brownfield areas
suitable for construction of for example houses, warehouses and tank
farms by reducing the residual settlement of the terrain
• Flood protection: Drains are used in the flood protection market to
increase the stability of dikes and embankments during widening projects.
Case Study:
• Site Location:
The site is located close to railway tracks on west side between
Nallasopara and Virar stations of Western Railways in MUMBAI.
The existing ground has been found to be susceptible to long
term settlements due to presence of 4 to 6 m thick caly layer. As
such ground improvement using PVD band drains were planned.
Case Study (Cont.):
Case Study (Cont.):
Specifications of PVD:
Sr. Description Unit Value
No.
1 Discharge Capacity M3 60 x10(-6)
2 Width mm 100+/-5
3 Thickness mm 3.5-5
4 Tensile Strength KN 2.0
5 Elongation at 2 KN % 25
6 Grab strength N 550
7 Puncture Strength N 150
8 Permeability Cm/sec 200 x10(-4)
9 Tear strength N 200
Case Study (Cont.):
Sr. NO. Description Unit Value
1 N.M.C % 33.88
2 Field Density Gm/cc 1.77
3 Gravel % 0 Test result of
4 Sand % 1.00 undisturbed
5 Silt % 49.0 soil sample
6 Clay % 50.0
7 Sp. Gravity - 2.78
8 Liquid Limit - 91.0
9 Plastic Limit - 23
10 Shrinkage Limit - 12
11 Plastic Limit - 68
12 Expected Settlement cm 51.99
Case Study (Cont.):
• Monitoring Scheme for checking Efficiency of the treatment:

The critical parameters to monitor during stage construction are
as follows:-
1. Build up dissipation of pore water pressure.
2. Rate and magnitude of vertical settlement.
3. Increase in shear strength and bearing Capacity of soil.
4. Time dependent strength and deformation characteristics.
Case Study (Cont.):
• Conclusion:
Ground Improvement by using PVD band drains resulted in
accelerated consolidation settlement. By using this technique
average settlement of 240 mm has been achieved in a period of
about 250 days.
Thank You!

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L.

D COLLEGE OF ENGINEERING AHMEDABAD

Preloading is an economical and

• Principle: To Accelerate drainage, typically used in soft, saturated

As stated by Terzaghi, the time taken for complete consolidation is a function

• Wick drains or PVDs consist of a

• Position Rig at Drain

Cutting of PVD after

• A pattern of installed vertical wick drains provides short drainage

1.Increased Rate Of Gain Of Shear Strength Of Clay:

• Monitoring Scheme for checking Efficiency of the treatment:

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