PREFABRICATED VERTICAL DRAINS GROUND IMPROVEMENT TECHNIQUE

PREFABRICATED VERTICAL
DRAINS (PVD)
In construction of various structures
on compressible, saturated soils
like soft clay, excessive settlement
is a common problem to deal with.
The ground improvement technique
using prefabricated vertical drains
(PVD) is one of the most suitable
methods to overcome this problem.
The sole purpose of vertical drain
system is to shorten the drainage
path of the pore water from a low
permeable layer to free water surface
or to pre-installed drainage
layer, thereby accelerating the rate
of primary consolidation or the process
of settlement. Application of
ground improvement method using
prefabricated vertical drains (PVD)
coupled with surcharge or preloading
can significantly shorten the
period of primary settlement.
SEAFCO
144 Prayasuren Road, Bangchan, Khlong Sam Wah, Bangkok 10510. Tel. (662) 919 0090-7, Fax. (662) 919 0098
EQUIPMENT
PVD installation equipment can be developed to suit the soil
condition, installation depth, specified scope of work and required
production rate. Technical data of typical medium-sized
PVD installation equipment and accessories are shown below.
Installation Rig
Type of Base Machine : Excavator of suitable model
CAT EL200B or larger model
Size (CAT EL200B) : 3.18m x 4.45m
Weight (CAT EL200B) : 20 ton
Pushing Force : 5.5 – 20 ton
Mandrel Lifting and Pushing : Hydraulic gear drive
Mast Height : 8m
Typical Mandrel Dimensions
Weight of Guide and Mandrel : 1.5 to 4 ton
Length of Mandrel : 12 to 20m
Cross-sectional Area of Mandrel : 60 to 70 cm2
Maximum Installation Depth : 11 to 19m
CHARACTERISTICS OF PVD
PVD is a prefabricated material
consisting of a plastic core covered
by synthetic geotextile “filter jacket”.
Two main components of PVD
serve the following functions;
• Core serves as a longitudinal
flow path along the drain
• Filter jacket allows water to
pass into the core while restricting
intrusion of soil particles
Time settlement curve of soft clay showing significant
time reduction achieved by applying PVD with
surcharge loading
TYPICAL APPLICATIONS
PVDs with surcharge as pre-loading
method has been successfully applied
in various projects. PVDs are
typically used as ground improvement
system in -
• Construction of road, railway,
embankment, airport and ports
• Industrial projects
• Land reclamation projects
Application of PVD with surcharge loading for ground improvement
work of road embankment
Time
Settlement
without PVD
PVD w ithout surcharge
required settlement PVD with surcharge
Surcharge
Final R oad Level
Dra inage S and Blanket P um p in g W e ll
SO F T C L AY P V D
Close-up view of
PVD installation
144 Prayasuren Road, Bangchan, Khlong Sam Wah, Bangkok 10510. Tel. (662) 919 0090-7, Fax. (662) 919 0098
SEAFCO
Reference:
• Hansbo, S. (1993), “Band Drains”, Ground Improvement, Blackie Academic Professional, U.K
• Center for Civil Engineering Research and Code (1996), Building on Soft Soils, A.A. Balkema, Rotterdam, The
Netherlands
All rights reserved. No part of this publication may be reproduced in any form or by any means, without
the prior written permission of SEAFCO PUBLIC CO., LTD.
QUALITY CONTROL IN
INSTALLATION
• Use appropriate size of
Mandrel and anchor plate
to minimize soil disturbance
• Use Mandrel with adequate
stiffness to maintain verticality
• Apply appropriate penetration
rate to avoid significant
bending
• Check verticality during installation
LAYOUT CONFIGURATION AND DRAIN INFLUENCE ZONE
PVDs are installed in either square or triangular patterns. A square
pattern is more simple for setting out in the field. Triangular pattern
however provides more uniform consolidation between drains.
Relationship of drain influence zone (D) to drain spacing (S) can be
expressed by;
For square pattern D = 1.13 S
For triangular pattern D = 1.05 S PVD equipment in operation
QUALITY CONTROL TEST
FOR PVD MATERIAL
• Apparent opening size
• Puncture resistance
• Burst strength
• Trapezoidal tear strength
• Grab tensile strength
• Discharge capacity (plain
and triaxial)
• Density of filter fabric
Installation sequence
Typical PVD layouts and drainage influence
Anchor
Plate
Position equipment and
anchor plate installation
Mandrel driving Mandrel extraction PVD cutting
D = 1.05 S D = 1.13 S
Triangular Pattern Square Pattern
PVD
PVD

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Soil Improvement

www.ce.washington.edu/…tml/how/soilimprovement.html

Soil Improvement

Earthwork and Ground Technology
Site Improvement
Slides adapted and upgraded from original presentation slide by College of Engineering, University of Washington.
Methods of site improvement
•Removal and replacement
•Preloading
•Vertical drains
•In-situdensification
•Grouting
•Stabilization using admixtures
•Reinforcement
Removal and replacement
•One of oldest and simplest methods is simply to remove and replace the soil
•Soils that will have to be replaced include contaminated soils or organic soils
•Method is usually practical only above the groundwater table
Preloading
•Simply place a surcharge fill on top of the soil that requires consolidation
•Once sufficient consolidation has taken place, the fill can be removed and construction takes place
•Surcharge fills are typically 10-25 feet thick and generally produces settlement of 1 to 3 feet.
•Most effective in clay soil
Advantages of preloading
•Requires only conventional earthmoving equipment
•Any grading contractor can perform the work
•Long track record of success
Disadvantages of preloading•Surcharge fill must extend horizontally at least 10 m beyond the perimeter of the planned construction, which may not be possible at confined sites•Transport of large quantities of soil required•Surcharge must remain in place for months or years, thus delaying construction
Vertical Drains
•Vertical drains are installed under a surcharge load to accelerate the drainage of impervious soils and thus speed up consolidation
•These drains provide a shorter path for the water to flow through to get away from the soil
•Time to drain clay layers can be reduced from years to a couple of months
Vertical Drains
PVD (Prefabricated Vertical Drain)
•Geosyntheticsused as a substitute to sand columns
•Installed by being pushed or vibrated into the ground
•Most are about 100 mm wide and 5 mm thick
Vertical Drain Installation
Photo from: http://www.joostdevree.nl/bouwkunde/vertical_drain_2_www_imtek_com_tr.jpg
Photo adapted from vertical drain supplier

Typical installation of PVD•Typically spaced 3 m on centersPrefabricated Drains Available in Malaysia•Nylex•Emaskiara•etc
In-situdensification
•Most effective in sands
•Methods used in conventional earthwork are only effective to about 2 m below the surface
•In-situmethods like dynamic deep compaction are for soils deeper than can be compacted from the surface
Dynamic vs. Vibratory
Compaction
sand
clay
Photo adapted from MonashUniv. CIV4249
Vibratory probe compaction
•Long probe mounted onto a vibratory pile driver compacts the soil around the probe; penetrations spaced in a grid pattern similar to vertical drains
Vibratory probe compaction
Photo by: Keller Holding
Beware of transmission of ground vibrations
Vibroflotation
•Probe includes the vibrator mechanism and water jets
•Probe is lowered into the ground using a crane
•Vibratory eccentric force induces densification and water jets assist in insertion and extraction
•Vibratory probe compaction is effective if silt content is less than 12-15% and clay is less than 3%
•Probes inserted in grid pattern at a spacing of 1.5 to 3 m
Photo by: Keller HoldingReclamation works -Singapore
VibroflotationGround Type Relative Effectiveness SandsExcellentSiltySandsMarginal to GoodSiltsPoorClaysNot applicableMine SpoilsGood (if granular)Dumped FillDepends upon nature of fillGarbageNot Applicable
Vibro-replacement stone columns
•Vibro-Replacement extends the range of soils that can be improved by vibratory techniques to include cohesive soils. Reinforcement of the soil with compacted granular columns or "stone columns" is accomplished by the top-feed method.
Vibroreplacement –JelutongExpresswayPhoto by: Keller Malaysia

Stone ColumnPhoto by: Keller Malaysia
Top-feed vibroflotrigAdding stone in top-feed installationBottom-feed vibroflotrigVibro-replacement stone columns
Dynamic compaction
•Uses a special crane to lift 5-30 tons to heights of 40 to 100 feet then drop these weights onto the ground
•Cost effective method of densifyingloose sands and siltysoils up to 15 to 30 feet deep
Grouting
•Defined as the injection of a special liquid or slurry material called grout into the ground for the purpose of improving the soil or rock
•Types of grouts
–Cementitiousgrouts
–Chemical grouts
Grouting methods
Intrusion grouting
–Consists of filling joints or fractures with grout
–Primary benefit is reduction in hydraulic conductivity
–Used to prepare foundation and abutments for dams
–Usually done using cementitiousgrouts
Permeation grouting
–Injection of thin grouts into the soil
–Once the soil cures, becomes a solid mass
–Done using chemical grouts
–Used for creating groundwater barriers or preparignground before tunneling
Graphicsource:Keller
Grouting methods
•Compaction grouting
–When low-slump compaction grout is injected into granular soils, grout bulbs are formed that displace and densifythe surrounding loose soils.
–Used to repair structures that have excessive settlement
Grouting methods
Jet grouting–Developed in Japan–Uses a special pipe with horizontal jets that inject grout into the ground at high pressures–Jet grouting is an erosion/replacement system that creates an engineered, in situsoil/cement product known as Soilcretesm. Effective across the widest range of soil types, and capable of being performed around subsurface obstructions and in confined spaces, jet grouting is a versatile and valuable tool for soft soil stabilization, underpinning, excavation support and groundwater control.

Stabilization using admixtures
•Most common admixture is Portland Cement
•When mixed with soil, forms soil-cement which is comparable to a weak concrete
•Other admixtures include lime and asphalt
•Objective is to provide artificial cementation, thus increasing strength and reducing both compressibility and hydraulic conductivity
•Used to reduce expansion potential of clays
•Used in surface mixing applications
A 500 m long embankment had to be constructed on a 4-5 m
thick, extremely soft, siltyclay layer of the Humber estuary at
Hull, Great Britain.Toguarantee the stability of the embankment,
soil improvement of the siltyclay was required. LCM offered a
geotechnicalsolution by means of dry-deep soil mixing.
Photo by: LCM/Keller
Reinforcement•Soil is stronger in compression than in tension•To improve strength in tension, geosyntheticsplaced in soil for soil reinforcement
Soft Soil
Kong, A.L.L. (2005), Jurutera, June 2005 No.6, IEM.
Soil improvement
Photo by A Naser Abdul Ghani
Soil improvement
Photo adapted from Bulletin Ingeniur
Reinforced earthwallconstruction
Soil Nailing
•The fundamental concept of soil nailing consists of reinforcing the ground by passive inclusions, closely spaced, to create in-situa coherent gravity structure and thereby to increase the overall shear strength of the in-situsoil and restrain its displacements.

Photo by A Naser Abdul Ghani

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Construction

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Construction