subsoils drainage and geotextile
DESCRIPTION
Subsoil Drainage and GeotextileTRANSCRIPT
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ECM 446
MUHAMMAD ADEEB SHAFIQ BIN IZAMUDDIN 2011102915
AHMAD SUHAILI BIN AHMAD TAJUDDIN 2011923111
KHAIRUL ANUAR YAAKOB 2011717765
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SUBSOIL DRAINAGE
Subsoil drainage systems are used in architectural, sewage and irrigation
applications to remove excessive water from the soil surrounding a building,
provide water to crops or drainage sewage away from a building.
Subsoil drainage systems are governed by necessary restrictions dependent
on the intended purpose of the system.
Subsoil drainage systems are
provided to drain away subsurface
water in order to:
Increase the stability of the
ground and footings of buildings by
inducing a more stable moisture
regime and reducing foundation
movements due to the variations inthe soil moisture content
Mitigate surface water
ponding and waterlogging of soils by
lowering watertables
Alleviate ground water
pressures likely to cause dampness
in below-ground internal parts of
buildings or damage to foundations
of buildings, other structures, or
pavements
Increase soil strength by
reducing the moisture content.
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Subsoil drainage is an important part of road construction. Vehicular
traffic on pavement with a saturated sub-base results in rapid deterioration of the
pavement. Entrapped water that is subject to vehicular loadings creates large
hydrostatic and hydrodynamic pressures within the sub-base, reducing its ability
to provide stable support for the pavement. Correctly designed roads and paved
areas have a highly permeable base or sub-base construction and may include
subsoil drains to promote the rapid outflow of sub-surface water.
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DRAIN TYPES
The types of subsoil drains that are commonly used are shown below. These may
be installed on flat ground, in a sag or depression, or on sloping ground.
The basic parts of a subsoil drain are shown in figure (a) which is a trench
with fill or filter material (commonly sand or gravel). This simple arrangement is
called a rubble drain or French drain.
Figure (b) shows the addition of a geotextile lining to prevent external fine
soil particles being washed into the filter material and clogging it. Both this and
the unlined rubble drain have only limited effectiveness due to their limited
ability to convey water.
Figure (c) shows the addition of a pipe to promote more rapid drainage.
This is the most common type of subsoil drain. The pipe is perforated to allow
easy entry of water and can be rigid or flexible.
Figure (d) shows two further variations, an impervious cap for situations
where the drain is intended to collect only subsurface flows, and bedding materialfor cases where the base of the excavation is unsuitable as a pipe support.
Figures (e), (f), and (g) show more elaboration. The pipe can be wrapped in
geotextile to prevent piping and loss of filter material. Geocomposite drains of
various configurations and manufacture can be provided. These are usually of
plastic wrapped in geotextile and various proprietary systems are available.
Finally, figure (h) shows an external layer of filter material provided around
the geotextile encompassing the filter material. This might be used where there is
a likelihood of fine particles or deposits, e.g. iron precipitates, clogging the
geotextile. In general, subsoil drains connect either into a stormwater pit or an
open channel which is part of a surface water drainage system, with the subsoil
drain pipe or strip drain penetrating the pit wall.
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(a) Basic System
(b)Geotextile Filter
Previous back fill
Geotextile layer
(c) Pipe Drain
(d) Pipe Drain with Capping to Exclude Surface Water
Impervious Cap
Fill or Filter
Material
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(e) Geotextile around pipe
Pipe Wrapped in Geotextile
(f) Geocomposite Drain in Narrow Trench
Vertical Geocomposite Drain
(g) Geocomposite Drain in Shallow Trench
Horizontal Geocomposite Drain
(h) Soil Filter Layer to Avoid Clogging of Geotextile
Pervious Filter Layer on Trench Sides
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Geotextile
What is Geotextile?
Geotextile are a subtype of geosynthetic material which is human-made
materials made from various types of polymers used to enhance, augment
and make possible cost effective environmental, transportation and
geotechnical engineering construction projects. They are used to provide
one or more of the following functions;
Separation,
Reinforcement,
Filtration,
Drainage
or Liquid barrier.
Specifically geotextile is flexible, textile-like fabrics of controlled
permeability used to provide filtration, separation or reinforcement in soil,
rock and waste materials.
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Types of geotextiles
1. Woven construction
Woven geotextile warp yarns, which run parallel with the length of the
geotextile panel (machine direction), are interlaced with yarns called fill or
filling yarns, which run perpendicular to the length of the panel.
From UFC, ENGINEERING USE OF GEOTEXTILES by the Department of
Defense of USA, 2004 ...Woven construction produces geotextiles withhigh strengths and moduli in the warp and fill directions and low
elongations at rupture. The modulus varies depending on the rate and the
direction in which the geotextile is loaded.
When woven geotextiles are pulled on a bias, the modulus decreases,
although the ultimate breaking strength may increase. The construction can
be varied so that the finished geotextile has equal or different strengths in
the warp and fill directions. Woven construction produces geotextiles with
a simple pore structure and narrow range of pore sizes or openings
between fibers.
2. Non-woven construction
Non-woven geotextile is formed by a process other than weaving or
knitting, and they are generally thicker than woven products. The fibers are
generally oriented randomly within the plane of the geotextile but can be
given preferential orientation. In the spunbonding process, filaments are
extruded, and laid directly on a moving belt to form the mat. These
geotextiles may be made either from continuous filaments or from staple
fibers.
Sub-types consists of needle punching, heat bonding, resin bonding,
combination bonding, and composite geotextile.
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Eg. of geotextiles
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Purpose of Geotextile
There exists at least 80 specific purpose of geotextile but it always perform
at least one of the following basic purpose which is:
Separation,
Reinforcement,
Filtration,
Drainage
or Liquid barrier.
One purpose of geotextile reinforcement is to hold the dike together until
foundation consolidation and strength increase can occur. Another purpose
is to reduce horizontal and vertical deformation.
A diversion ditch is an open, artificial, gravity flow channel which intercepts
and collects precipitation runoff, diverts it away from vulnerable areas, and
directs it toward stabilized outlets. A geotextile or revegetation mat can beused to line the ditch.
Permeable geotextile silt fence is used to intercept and detain sediment
from unprotected areas before it leaves the construction site. It is placed
around the entire downslope portion or perimeter of urban construction
sites.
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Eg. of application
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Designing with Geotextile
Consider a geotextile under an embankment
This geotextile may function simultaneously in filtration, separation,
drainage and reinforcement
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REFERENCE
1. USA, Department Of Defense. 2004 : UFC Engineering use of Geotextiles2. USA, Tensar. 2014 : GEOSYNTHETHICS IN CIVIL ENGINEERING