Prefabricated vertical drain

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Prefabricated vertical drain

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UNIVERSITI TUN HUSSEIN ONN MALAYSIA
CENTER OF DIPLOMA STUDY
ASSIGNMENTS
(LATEST TECHNOLOGY IN SOIL IMPROVEMENT USING PREFABRICATED VERTICAL
DRAINAGE METHOD)

SUBJECT CODE : DAB 20702 AMALAN TEKNOLOGI SUBSTRUKTUR DAN
CERUN

GROUP

:1

MEMBERS

:
NAME
AKASHAH BIN RIDZUAN
AMIRUL DANIAL BIN SAMSUDIN
FARAH HANI BINTI MD SIDEK
FATIN HAZWANI BT MOHD ZULKIFLI

LECTURER : EN. AHMAD HAKIMI

NO. MATRIC
AA130936
AA130190
AA130008
AA130098

1. Introduction
Prefabricated Vertical Drains (PVD) and Vertical Strip Drains (VSD)
also known as Wick drains, are a ground improvement technique that
provides drainage paths for pore water in soft compressible soil, using
prefabricated geotextile filter-wrapped plastic strips with molded
channels. A hollow mandrel is mounted on an excavator or crane mast.
The wick drain material, contained on a spool, is fed down through the
mandrel and connected to an expendable anchor plate at the bottom of
the mandrel.
A vibratory hammer or static method is used to insert the mandrel
to design depth. The mandrel is then extracted leaving the wick drain in
place. The wick drain is then cut at the ground surface, a new anchor
plate is connected to it and the mandrel moved to the next location. A
pattern of installed vertical wick drains provides short drainage paths for
pore water, thereby accelerating the consolidation process and the
construction schedule.
The use of prefabricated vertical drains with preloading is now
common practice and is proving to be one of the most effective ground
improvement techniques known. The factors affecting its performance,
such as the smear zone, the drain influence zone, and drain unsaturation,
are discussed in this paper. In order to evaluate these effects a large scale
consolidation test was conducted and it was found that the proposed
Cavity Expansion Theory could be used to predict the characteristics of
the smear zone based on the soil properties available. Moreover, the
procedure for converting an equivalent 2-D plane strain multi-drain
analysis that considers the smear zone and vacuum pressure are also
described.
The conversion procedure was incorporated into finite element
codes using a modified Cam-clay theory. Numerical analysis was
conducted to predict excess pore pressure and lateral and vertical
displacement. Three case histories are analysed and discussed, including
the sites of Muar clay (Malaysia), the Second Bangkok International Airport
(Thailand), and the Sandgate railway line (Australia). The predictions were
then compared with the available field data, and they include settlement,
excess pore pressure, and lateral displacement.
The findings verified that smear and well resistance can significantly
affect soil consolidation, which means that these aspects must be
simulated appropriately to reliably predict consolidation using a selected
numerical approach. Further findings verified that smear, drain
unsaturation, and vacuum distribution can significantly influence

consolidation so they must be modelled appropriately in any numerical
analysis to obtain reliable predictions
Preloading is the application of surcharge load on the site prior to
construction of the permanent structure, until most of the primary
settlement has occurred. Since compressible soils are usually
characterized by very low permeability, the time needed for the desired
consolidation can be very long, even with very high surcharge load.
Therefore, the application of preloading alone may not be feasible with
tight construction schedules and hence, a system of vertical drains is
often introduced to achieve accelerated radial drainage and consolidation
by reducing the length of the drainage paths.
2. Litreture review
2.1 Theory of Vertical Drains
The basic theory of radial consolidation around a vertical drain
system is an extension of the classical one-dimensional consolidation
theory. Barron (1948) studied the two extreme cases of free strain and
equal strain and showed that the average consolidation obtained in both
cases are nearly the same. The “free stain hypothesis” assumes that the
load is uniform over a circular zone of influence for each vertical drain,
and that the differential settlements occurring over this zone have no
effect on the redistribution of stresses by arching of the fill load. The
“equal strain hypothesis” on the other hand assumes that the load applied
is rigid and equal vertical displacement in enforced at the surface, i.e.
horizontal sections remain horizontal. The solution for the second case is
considerably simpler (Barron 1948)

2.2 Properties of the filter
In general, the drain material of a sand drain and the filter jacket of
a prefabricated drain have to perform two basic but contrasting
requirements, which are retaining the soil particles and at the same time
allowing the pore water to pass through. According to Hansbo (1979,
1994), the filter has to meet the following requirements:
• the permeability of the filter should be high enough not to influence the
discharge capacity of the drain system,
• on the contrary, the permeability of the filter should be low enough to
retain fine soil particles. The soil particles might penetrate through the

filter into the core, which eventually might be filled with soil and get
clogged,
• the filter needs to be strong enough to withstand high lateral pressure
in order not to be squeezed into channel system of the core
• the filter should be strong enough not to break during installation, and
• the filter should not deteriorate with time because this would reduce the
discharge capacity of the drain

3.0 Method

procedure

3.1 Sequence of
drainage wick

vertical
installation

Fig. 6.1 Installation
wick drains

All

vertical
will
go
to
allowable/anchor
until refusal as per
method:-

equipment for

drainage wicks
maximum
able depths or
following

a)
Thread
the
vertical
drainage wick off the wick roll/spool, up the wick tube, and over the top
wick roller and down through the mandrel.
b) Place the drainage wick through or around the anchoring device and
tuck the loose end of the wick up into the mandrel about 6 to 8 inches
(150 to200 mm). Pull the drainage wick’s excess slack tight through the
mandrel and vertical drainage wick tube by reversing the vertical drainage

wick roll by hand. By reversing the vertical drainage wick spool or wick
roll, the anchoring device will retract up tight against the bottom tip of the
mandrel. This will prevent dirt or mud from entering the mandrel during
the insertion of the mandrel into the ground.
c) Move the machine/mandrel to the specified vertical drainage wick
locationand insert the mandrel with anchoring device in place using static
force(and /or vibratory force if necessary) into the ground to the desired
depth.
d) Extract the mandrel, leaving the anchoring device and the completed
or installed vertical drainage wick in place, uncontaminated and the
properdepth.
e) Cut the vertical drainage wick off the contract-specified length above
the working surface’s)
Check the vertical drainage wick installation machine mast to make sure
it is plumb. Use hydraulic controls to correct if not with the specification

Fig. 6.2 Installation of drain.
3.2 Splicing vertical drainage wick
Vertical drainage wick is supplied on wick rolls. Each wick roll will hold
about1000 ft. of drain or 305 m. Once the wick roll is used off, a splice is
necessary to add thenext wick roll. To splice, cut the end of the previous
wick roll at an angle and stuff it insidethe end of the new wick roll. Then
staple them both together as shown in figure.

Fig. 6.3 Splicing of wick drains

4.0 Discussion on the method
A vertical drainage system can be installed in order to accelerate
the
consolidation process and help to improve discharge of excess pore pressu
re in the sub soil. In this way, a stable situation is reached more quickly,
thus shortening the filling time dramatically. At the same time, the
settlement process is accelerated to such an extent that earthwork
finishing off processes can be started earlier.
All of these results in a substantially shorter construction time which
may be important both economically and socially. The installation of
vertical PVC drains is usually done with the aid of a dragline fitted with
tams along which the lance can move up and down vertically. The length
of drain to be installed determines the minimum length both of the
equipment and of the lance. The drains are wrapped around a coil which is
placed in housing in the rig. From there, the drain passes over a travel
roller until it feeds into the top of the rig and then via second travel roller
through the lance downwards.
Beneath the lance, a small anchor platies secured to the drain. The
lance is then installed to the desired depth either by vibration or with the
help of a static pressure and tensioner. Any solid layer encountered can be
pre- jetted. The anchor plate ensures that the drain, once to depth,
remains at that depth whilst the lance is being withdrawn. The drain is
then clipped off above ground level, after which the entire procedure can
be repeated all over again at the next drain location. Depending upon soil
conditions, the length & width of the drain strip, an output of 2000 to
6000linear m per eight hour work day per rig can be achieved.

5.0 CONLUSION

Each and every project is unique due to its features, geographical
locations and importance; hence while adopting one variety amongst
various available alternatives, precautions should be kept in view. In
addition, while deciding the method to be adopted for enhancing the
process of consolidation, the economy aspect, time available for
construction and availability of various materials should be considered.
The need of the method depends upon the time frame for
completion of project. If project is to be completed early; the stage
construction cannot be employed. For such cases, the methods for quick
consolidation of sub-soil have to be adopted using PVC vertical drainage
system. In case, when no time constraint is there, installation of sand
drains with stage construction after proper design can be adopted
The technology surrounding the use and application of prefabricated
vertical drain is continually growing. The concept of vertical drainage
utilizing prefabricated fdrains has been applied to many non-traditional
applications

6.0 References





https://www.academia.edu/5418048/Prefabricated_Vertical_Drains_MLMCE_1_Civil_Engineering
http://www.docstoc.com/docs/73459057/PRE-FABRICATEDVERTICAL--DRAIN--(PVD)
http://www.americandrainagesystems.com/images/wick_drain_install
ation.htm
http://www.uswickdrain.com/



http://www.wicks.nl/vertical-drainage

7.0 Appendices

1 Machines installing the wick drain

2 Water come out from land through fabricated drainage

3Area of land installed with fabricated wick drain

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