subsoils drainage and geotextile

5/27/2018 Subsoils Drainage and Geotextile

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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

subsoils drainage and geotextile

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