REAM Guidelines for Road Drainage Design - Volume 5

FOREWORD

Road

Engineering

Association

of

Malaysia

(REAM),

through

the

cooperation and support of various road authorities and engineering

_{institutions in}

Malaysia, publishes

A SETiES Of OffiCiAl documents on

_{STANDARDS, SPECIFICATIONS, GUIDbLINES,}

MANUAL

and

TECHNICAL

NOTES

which

are related

to

road engineering.

The

aim

of

such

publication

is to

achieve

quality

and consistency

in

roa-d and highway construction, operation and maintenance.

The _{cooperating bodies}

are:-Public Works Department Malaysia

(pWD)

Malaysian Highway

Authority

(MHA)

Department of

krigation

&

Drainage

(DID)

The

Institution

of Engineers Malaysia

(IEM)

The

Institution

of Highways

&

Transportation

(IHT

Malaysian Branch)

The production

of

such documents is carried through several stages.

At

the Forum on

Technoiogy and Road Management organized

by PWD/REAM

in

Novemb

er

I99J,

Technical Committee 6

_-

Drainage was formed

with

the

intention

to

review Arahan

Teknik (Jalan)

15/97

_-

INTERMEDIATE

GUIDE

To

DRAINAGE DESIGN

oF

ROADS. Members

_of

the

committee

were drawn

from

various

government

departments

and

agencies,

_{and from the private}

_sector

_{inciuding privitized}

_road

operators, engineering consultants

and

drainage

products

manufacturers

and contactors.

Technical Committee

6

was

divided into

three

sub-committees

to

review

Arahan

Teknik

(Jalan) 75/91

and

subsequenrly

produced 'GUIDELINES

FoR

ROAD

DRAINAGE DESIGN'

consisting of the

following

volumes:

Volume

I

_-

Hydrological Analysis Volume 2

_-

Hydraulic Design

of

Culverts

Volume

3

_-

Hydraulic Considerations in Bridge Design Volume 4

_-

Surface Drainage

Voiume

5

_-

Subsoil Drainage

The drafts

of all

documents were presented at workshops

during

the Fourth and

Fifth

Malaysian Road Conferences held

in

2000 and 2002

respectively.

The comments and suggestions received

from

the workshop participants were reviewed and incorporated

in

the finalized documents

ROAD ENGINEERING ASSOCIATION

OF

MALAYSIA

46-4,

Jalan Bola Tampar 13/14, Section 13,40100 Shah

Alam,

selangor, Malaysia

Tel:

603-5513

652r

_Fax:5513

6523

_e-mail:

_{ream@pojaring.my}

-J-5.1

<)

5.3 5.8.2 5,8.3 s"8.4

TABLE

_{OT CONTENTS}

pase

INTRODUCTION

...5-1

PROVISION AND LOCATION

_{OF SUBSOIL}

_DRAINAGE...

... 5.1

DESIGN

_{OF SUBSOIL}

_DRAINAGE

_SYSTEMS...

..".,..5-2

5.3.1.

The Control

of

Seepage

_{Flow in Rollins}

or _{Mountainous Terrain}

_...

5'3'2

The

_{conrrol of}

_a

_High

_wut",

_,"or"tr

_ar",

_,".rt*.

_.

tuX 5.3.3 _{The Control of Water Entering the Subgrade}

Through a

Pervious Road

Surface...

. .

DESIGN

_{FLOW CAPACITY}

5.4.1

Field

Trial

Method.

5.4.2

_{Calculation Method}

5-2 5.4

3.t

DETAILED

_SUBSURFACE

_{INVESTIGATION...}

5-8

5.5.1

Boring

and Ground

WaterLevel

_{Measuremer;:..."...5_g}

5 .5

.2

Standpipe

. . .5_g

5.5.3

Piezomerer

Standpipe

. _" ..5_g

DETERMINATION

_OF

_{SOIL COEFFICIENT}

OF'

PERMEABILITY

_....5-9

5.6.1

In-situ

permeability _Test

(a)

Variabie Head

in

Soils...

_{...5_9}

(b)

PackerTesrinRock"...;

...5_10

DESIGN

OF

_{FILTER MATERIAL.}

_.

..,,5-1]

5.7

.l

_{Design Filter Marerial - standarJ}

C.rai"g"rd'Design

_{Grading . ...5_r7}

5.7

.2

_Synthetic

_Filter

_Clorh

_/

_Fabrics

...5_20

5.7.3

Examples of

FilterDesign.

..."5_23

TYPES OF SUBSOIL

DRAINS

...

_....5-27

5.8.1

Single Size Aggregates

Filled

Trench

Lined

with

Synthetic

Filter

Cloth (See _{Fig. 5.15)}

_...

-t

I I

-l

I I 'I I I I I I 1 I I I I t

;*--Subsoil Pipe and Single _{Size Aggregate}

_Filled

_Trench Lined

with

Synthetic

Filter

_{Ctottr qsie Fig. 5.16)}

_...,

Porous / Perforated

/

Slotted pipe

with

Design

_{Filter Material}

_{(See Fig.5.17)}

_...

Other Proprietary _Types

.. _"....5-21

5-28

.5-28

5-28 5.9

DRAIN

PIPE

DESIGN

LIST

OF FIGURES

Fig.

5.1

Longitudinal

Subsoil Drain used to cut

off

seepage and

lower

the groundwater table

.

...

' '5-3

Ftg.5.2

MultipleSubsoilDrain.

...:

....5-3

Fig.

5.3

Symmetrical

Longitudinal

Drains used to

lower

the water table

.

...5-3

Fig.

5.4

Subsoil

Drain for

Multilanes

Road

"...

'..5-4

Fig.

5.5

Sunsoil Drain to

directly

drain the base course

...

...5-4

Fig.5.6

Interception

of

Shallow Seepage

Zone

.

...5-4

Fig.

5.7

Subsoil Drainage Layers

for

High

Fill

..

.."...5-5

Fig.

5.8

Standpipe

Installation

...5-11

Fig.

5.9

Piezometer Standpipe

Installation

--""....5-I2

Fig.

5.10Nomograph

for

Estimating Coefficient

of

Permeability

of

Granular

Drainage and

Filter

Materials

.

_'..5-13

Fig.

5.11 Particle Size

Distribution for

Concrete Sand B.S. 882

Filter

Material Recommended

for

Clay

Soils

..5-19

Fig.

5.l}Gradation

of

Filter

Material

..5-24

Fig.

5.13

Filter

and Slot Design

for

Example 2

...

...5-24

Fig. 5.14Filter

Design

for

Example 3.. .

Fig.

5.15 Single Size Aggregate

Filled

Trench

Lined

with

Synthetic

Filter

Cloth..

...5-31

Fig.

5.16 Subsoil Pipe and Single Size Aggregate

Filled

Trench

Lined with

Synthetic

Filter

Cloth

. .5-31

Fig.5.17Porous

/Perforated/

SlottedPipe

withDesignFilterMaterial.

...5-32

Fig.

5.18Examples of Arrangement of Transversesubsoil

Drain

...5-32

Fig.

5.19

Typical

Pipe Outlet

for

Subsoil

Drain

. . ....5-33

LIST

OF

TABLES

Table

5.1

Normal Range of Permeability

Coefficient

of

Typical

Soils

.

. ... . . .5-7

TabIe

5.2

Insitu Permeability Test

_-

(Variable

Head).

"...

"5-1'4

Table

5.3

Field Permeability Test

_-

Packer

Test

.

... _'5-15

Table

5.4

Measurement of

W.L. for

Standpipe/Piezometer

Standpipe

...5-16

Table

5.5

The Particles Size

Distribution

for

Concrete Sand

MS

30

....5-18

Table

5.6

Composition of Sand Fraction

from

150 gm Samples ...

...

" .

.5-2I

5.1

INTRODUCTION

Water

control

is

a

very

important factor

in

highway

_{design and construction.}

Although

_{adequate surface drainage}

_is

_the

_firsl

_step

_in

eniuring

good internal

moisture control,

a

properly

designed

and

incorporated

_,uu*it

_drarnage system

is

also essential.

Soil is

a natural material made up

of

solid particles and various sizes

of

pores, such that water either _remains

_in

_it

_or

_{perlolates through}

_it.

water

retention and movement

within,

constitute

the

two

important

phases

_in

_soii

_moisture

relationship'

_Water

_{movement takes}

_place

_fy

_trr"

action

of

gravity

or

of

capillary

_{action, or}

_by

_{a combination}

_of

_the

_two.

_Subsoil

drainaie

can

r"duc"

the

soil

moisture

_by

_{keeping the ground water}

_table

_well

beneith

the paved surface.

The

principal

objective

_of

subsoil drainage

is

to make sure that a subgrade

of

uniform

_{bearing value and strength is maintained.}

The

principal

ways

in

which

changes

in

moisture

conrent

can occur

in

the subgrade

of

a road are:_

VOLUME

5,

_{SUBSOILDRAINAGE}

by

lhe seepage

of

water

into

the subgrade

from

higher ground adjacent

to the road (a case

of

seepage

_flow

_{in roriing}

_{or *o"'rrtui".rous terrain);}

by

a

rise

or fall

in

the level

of

the water

table (a

case

of

high

water table

in

a

flat

terrain);

by

the

percolation

of

_water

_through

_the

_surface

_of

_the

road carriageway.

(a)

(b)

(c)

<)

_{PROVISION AND LOCATION}

OF SUBSOIL

DRAINAGE

The

decision

_{to install}

_{subsoil drainage should}

_be

based

on

site

conditions

existing

at

the

time

of

_{construction. where position}

_oi

_,t

"

water table

is

reasonably close

to

formation

level

(about

_im

or

less), the

Engineer

is

required

to

carry

_{out soil}

classification

tests,

grading

tests and

trial pits

to ascertain the

level

of

the water

table.

The

mosiapprolriut"

time

for .uoylng

out the

trial

pits is during _{the wet months when ttre}

_iater

_{table is}

_usualy

_at

_iti

highest

level

and

the

subsoil

at

its

wettest.

It

is

the responsibility

_of

the

Engineer

_to

_determine

_the

_{necessity and locations}

where

subsoil drainage is

rcquired'

_{The Engineer then}

_foliows

_{the procedures}

specified under Section

5.7

in

order

ro

select and design

firter

material suitabi"

f*

_{ih;'^ryp"ffi"rr}

encountered.

5.3

DESIGN

OF SUBSOIL DR.AINAGE SYSTEMS

Subsoil drainage is required for the

following

conditions:

intercepting seepage water

from

outside sources and

lowering

it

to acceptable level before

it

reaches the road structures (see

Fig.

5.1); the removal

of

stationary water

in

the soil

to

control

and

to lower

the ground water table and

providing

outlets (see Fig. 5.3 and

Fig.

5.4); (a)

(b)

(c)

to

drain the

subgrade and pavement

during

and after

the

construction period (see Fig. 5.5).

5.3.1

The

Control

of Seepage

Flow

in Rolling or

Mountainous

Terrain

There are

two

methods

of

dealing

with

the

condition

of

seepage

flow.

If

the

seepage zone

is

narrow

and

within

1m

of

the

surface then the

usual procedure

is to install

an

intercepting

subsoil drain

just

in

the

impermeable strata underlying

the

seepage zone as shown

in

Fig.

5.1.

If,

however,

the

seepage zone

is wide or

the

impermeable stratum is

deep,

it

is

generally,

impracticable

to

construct

the

drainage trench

sufficiently

deep to intercept all the seepage water.

ln

this

case, therefore, the

intercepting

drain

is

usually located to keep

the leve1

of

underground water

table about

1m

below formation

level

(see Fig. 5.1).

Where

roads are

on

sloping ground,

longitudinal

drains may

not

be capable

of

intercepting

all

the seepage

water. In

such cases,

it

may be necessary to install horizontal

filter

blankets as shown in

Fig.

5.7.

5.3.2

The

Control

of a

High Water

Table

in Flat Terrain

A

high

water table can

be

lowered

by

the installation

of

subsoil

drainage

system.

It

is

desirable

that the

water table should

be

maintained at a depth not less

than

1m

below

formation

level

(see Fig.

5.3).

The

actual spacing

and

depth

of

drains

to

achieve

this

requirement

will

depend

on the

soil

conditions and

width of

the road

formation. In

the case

of

dual carriageways, drains may be necessary

under the central reserve as

well

as under the edges

of

the

formation

(see

Fig.

5.a).

5.3.3

The

Control

of

Water Entering

the Subgrade

Through

a Pervious Road

Surface

A

completely

impermeable

road

surface

is

difficult

to

reaiize in

practice and porous

subbase

has been installed

to

deal

with

water

[

ORTGTNAL GROUND

\ J

IPROPOSED CUT SLOPI

ORIGINAL WATER TABLI

t\l -\l

-i-.\.\'_\

DRAWDOWN CURVT SUESOIL DRAJN DRAWDOWN CURVT SUBSOIL DRAIN

FIG.

5.2

MUITIPIE

SUBSOIL DRAIN

ORIGINAL WATTR

FORI/ATIONLEVEL

\

I

TABLI

p*o*00**;;;:l-Li:0HffilJof,Y-J[;--L

rMpERVr.us B',NDAR'

nG.

5.3

THE

TATER

TABIE

PROPOSTD _{CUT SLOPI}

NG. 5.4

SUBSOII

DRAIN

FOR

MUTTII,ANES ROAI) SHOULDER SUBBASE DESIGN FILTER l'/ATERIAL MINIMUM 150mm

0

SUBSOIL PlPt

FIG.

5.5

SIESOIT

DRAIN

TO

DIRECTTY

DRAIN

TIIE

BASE

COT]RSE

WATIRTABLE ROADSIDI DRAIN SETPAGE ZONE IMPIRVIOUS STRATUM

DESIGN FILTER MATERIAL

l/lNiMUM 150mm

0

SUBSOIL PIPE

NG"

5.6

IIVTERCEPTION

OF

SHATLOT SEEPAGE ZONE

SHOULDER

o

54

v 1 1 i

-l !-ll Fll lE{l I CJI I

pll

E{l I

u)l

fEll

>l

<t

Fll

I

HI

(5l

<l

zl

<l

EI

al

-l (t)l

ql

DI

Ql

t\

.ri

ri F={ F :<

z

J m

o

z

(/) l< = F J

r

)< (J o o = -z

;{-E c)o F =E z-UF cD< co ,U)^ 4zz. w X!2 ^TU IL z. l l<J

PB3

C)> L! LrJ

dog

o<=:

epER

oYs6

e<5tr= LLLD>< z. A Lr) =J L! LT ooa F {r,r

>--IJ'\ J LI U) o_ J (n o i! a e z.

5

m t L!

t

E z. t O J

6

(/) I co f a z. E o U a O 1.s (MAX)

)-)

5.4

5.3.3

The

Control

of

Water Entering

the

Subgrade

Through

a

Peryious

Road

Surface

-

(Cont'd)

(a)

Porous Subbase

The

purpose

of

the

porous, granular subbase

is to

trap

any water

infiltrating

through the road surface and carry

it

to the open drains

provided beyond the road shoulders and so prevent the softening

of

the subgrade. The porous subbase consists

of

i50mm

to 300mm

of

compacted

porous rnateriai

such as sand,

gravel, etc.,

interposed

between

the

base course

and

the

subgrade (see

Fig.

5.5).

The subgrade, has

to

be properly

cambered and

free

from

depressions

and the porous subbase must cover

the

entire road

formation

and connected

to the

roadside

drain.

Unless

very careful

attention is

given

to

the shaping and cambering

of

the subgrade,

it

is probable

that

most

of

the water

passing

into

the

porous subbase

would

be

trapped

in

irregularities

in

the

surface

of

the

subgrade, and consequently not entering the drain.

Besides acting as a drainage layer, the porous subbase increases the

thickness

of

the

pavement

design.

It

also

prevents

soft

clay

working

up

into

the base course

of

a

flexible

pavement founded on a

ciay subgrade.

It

is

placed

immediately

after the preparation

of

the formation, and

will

help

to

prevent

the

disturbance

of

the subgrade

by

construction

traffic.

It

is

probable that the improved

performance of roads

with

porous subbase is due to the latter factor

rather than the possibie drainage,

which

the subbase effects.

DESIGN

FLOW CAPACITY

Commonly, the design

flow

capacity

of

ground water drainage system is based

on empirical

rule

of

thumb that have been developed

by

trial

and error over a

period

of

years,

or

on rather tedious graphical techniques

involving

the use

of

flow nets.

The

purpose

of

this

section

is to

present

a field

trial

and error

method and an approximate analytical method.

5.4.1

Field

Trial Method

Where earthwork has reached

formation level,

a useful estimate

of

the

effect

of

installing

drains

to

lower the

level of

the

ground water

at

a

particular site (see

Fig.

5.3) can be obtained

by

carrying out

a simple

field

trial.

Two parallel

trenches 500mm

wide

and about 20m long are

.

_{dug along the}

_{line of}

the proposed drainage trenches

for

the road

to

a

depth

of

about 1m

below

the leve1

to

which

it

is

desired

to

lower

the

ground

water.

A

transverse

line

of

boreholes

at

about

1.5m

to

3m intervals

is

sunk between the centre

of

the trenches and extended about 3m to 6m either

side.

Observations are made

of

the levels

of

the water table

in

the boreholes

before

and

after pumping the water out

of

the

trenches

for a

sufficient period

of

time

to

establish equilibrium

conditions. By plotting

these results, an estimate can be made

of

the

drawdown effect

of

the drain trenches, and

by this

means

it

is possible

to

establish the correct depth and spacing

of

the

drains.

The capacity

required

for

the drainpipes can be estimated

from

the rate

of

pumping

necessary to keep the trenches free

of

water.

5-6

x

:l I

5.4

5.3.3

The

Control

of

Water Entering

the Subgrade

Through

a

Pervious Road

Surface

-

(Cont'd)

(a)

Porous Subbase

The

purpose

of

the

porous, granular subbase

is to

trap

any water

infiltrating

through the road surface and carry

it

to

the open drains

provided beyond the road shoulders and so prevent the softening

of

the subgrade. The porous subbase consists

of

150mm to 300mm

of

compacted

porous material

such as sand,

gravel, etc.,

interposed

between

the

base course

and

the

subgrade (see

Fig.

5.5).

The

subgrade. has

to

be properly

cambered and

free

from

depressions

and the porous subbase must

cover the

entire road

formation

and connected

to

the roadside

drain.

Unless

very careful

attention is

given

to

the shaping and cambering

of

the subgrade,

it

is

probable

that

most

of

the

water passing

into

the porous subbase

would

be

trapped

in

irregularities

in

the

surface

of

the

subgrade, and consequentiy not entering the drain.

Besides acting as a drainage layer, the porous subbase increases the

thickness

of

the

pavement

design.

It

also

prevents

soft

clay

working

up

into

the base course

of

a

flexible

pavement founded on

a

clay subgrade.

It

is

placed

immediately

after the preparation

of

the formation, and

will

help

to

prevent

the

disturbance

of

the subgrade

by

construction

traffic. It

is

probable that the improved

performance of roads

with

porous subbase is due to the latter factor

rather than the possible drainage, which the subbase effects.

DESIGN

FLOW CAPACITY

Commonly, the design

flow

capacity

of

ground water drainage system is based

on empirical

rule

of

thumb that have been developed

by

trial

and

effor

over a

period

of

years,

or

on rather tedious graphical techniques

involving

the use

of

flow nets.

The

purpose

of

this

section

is

to

present

a field

trial

and error

methocl and an approximate analytical method.

5.4.I

Field

Trial Method

Where earthwork has reached formation

level,

a useful estimate

of

the

effect

of

installing

drains

to

lower the level

of

the

ground water

at

a

particular site (see

Fig.

5.3) can be obtained

by

carrying out

a simple

field

trial.

Two

parallel trenches 500mm

wide

and about 20m long are

.

_{dug along the}

_{line of}

the proposed drainage trenches

for

the road

to

a

depth

of

about 1m

below

the

levei

to

which

it

is

desired

to

lower

the

ground

water.

A

transverse

line

of

boreholes

at

about

1.5m

to

3m intervals is sunk between the centre

of

the trenches and extended about 3m to 6m either

side.

Observations are made

of

the levels

of

the water table

in

the boreholes before and after

pumping the water out

of

the

trenches

for

a

sufficient period

of

time

to

establish equilibrium

conditions. By plotting

these results, an estimate can be made

of

the

drawdown effect

of

the drain trenches, and

by this

means

it

is possible

to

establish the correct depth and spacing

of

the

drains.

The capacity

required

for

the drainpipes can be estimated

from

the rate

of

pumping

necessary to keep the trenches free of water.

5-6

s.4.2

_{Calculation Method}

It

is

always

desirabre

_to

_{carry out}

_design

_flow

_carculations

for

the

following

reasons:-to predict _{the reduction}

_in

_{the water}

level

due

of _{subsoil drainage;}

severe _cases

_where

_project

area

excessive seepage.

is of

high

water table

or

application

_of

_the

_law

_needs

determine

_the

_permeability

(a)

(b)

to

the provision

Darcy's

Law

is

_{commonly used}

_and

detailed

_subsurface

_{investigatio"--.;;}

constant (k).

calculation

_of

_design

_flow

_is

_sometimes

omitted

in

the

design

of

subsoil _{drainage. This is due to the}

faci

that sorvinJ rrr"

d",

equations under complicated actual _{ground conditions is}

_difficult.

Darcy's

_Law:

a

where

_a

k

A

i

=

kiA

=

seepage volume (cu.cm/sec)

=

coefficient

_{of permeability (cm/sec)}

=

cross sectional area of seepage layer (sq.cm)

=

hydraulic gradient The application

_of

_Darcy's

_{Law is}

_sufficient

for

most subsoil _drainage although

_it

_{assumes raminar}

_flow

_anJ-.onstant

viscosity

of

the water.

The

use

of

Darcy's

_{Law requir",}

_u

_{i"r"rroination or}

tne permeability

constant

(k)

and the

hydraulic

gradient

_{(i) u"J}

_tr,"r.

_*";;r"es

are not easily _{obtainable under}

foln]i_la1eo

grouno

conditions. so,,'"

typical

values

for (k)

_{are shown}

_in

_Table

_5.1."

Table

5'1

-

_{Normar Range of}

permeab'ity

_coefficient

of

rypicar

so's

Source: Japan Road Association

0.1

-

1.r

10-Sandy Soil 0.1

r

10-'-

1x

10

Clayey Soil

0.1,r105-1x10-Very low permeability

0.1 x 10-' or less

5.5

DETAILEDSUBSURFACEINVESTIGATION

5.5.1

Boring

and

Ground Water

Level Measurement

Boring

and Ground Water Measurements should be done at the project

area

to identify

the

underground

conditions

and

level of

water table.

For

water

ievel

locations

when

earthworks have

reached formation

level,

drilling

a

hole

by a

small

auger should

be

sufficient. Measurement

of

the

water table

is

a

very

important part

of

the

sub surface investisation.

The water

level

in

every borehole

is

taken

while

drilling

is in

progress at the

following:-(a)

before

work

commences

in

the morning;

(b)

after

work

finished

in

the evening

but

before water

is

added to the borehole.

The

depth

of

the borehole and

the

casting

(if

any)

is

measured when

each water level measurement is taken"

5.5.2

Standpipe

Standpipe

of

19mm internal diameter

rigid

unplasticised P.V.C. tubing can

be installed

in

selected boreholes

especially directed.

(See Fig.

s.8).

The bottom

of

the

standpipe

is

plugged and

the

lower 0.5m

is perforated

with

slots.

The perforated

tubing is

surrounded

by

a response zone

of

an approved

granular

material

used

to

backfili the

borehole

to

a

depth

of

1.5m

beiow ground level.

The top

of

the

P.V.C. tubing is

then sealed

with

a steel cap to prevent

the ingress

of

surface water.

5.5.3

Piezometer

Standpip.

,

The piezometer standpipe consists

of

a porous element 305mm

long.

It

is

saturated before

placing

and

is

placed

centrally

in

a response zone

consisting

of

1.0m deep layer

of

well-graded

fine

to coarse sand and is tamped

below

and above the porous

element.

The porous element is connected

to

19mm internal diameter

rigid

unplasticised P.V.C. tubing

which finishes

close

to

ground

level.

A11 the

joints in

the

tubing

are

made

with

coupling

sleeves so

that

there

is

no

change

in

the internal

diameter of the bore and

it

is sealed to be watertight.

5-8

,i

5.6

5.5.3

Piezometer

_Standpipe

_

_(Cont,d)

The borehcire is then seared _{above the response}

_zone.

A stiff

grout seal

of

_{bentonite 0.5m}

_{thick is}

_{rhen formed}

!y

_";;;ry

a"poriting

;

**;;

freshly mixed

grout.

_{The remainder}

_of

_{irr" ,"ui}

_is

_tormea

by

pracing

grout

through

a

tremie tube,

_{the iower}

_eno

_oi

_{,ti.t, ,hul'f,"ffi}

below the surface

of

the

grout.

_{The grout}

_is

_{then alrowed to}

settre and

set

for

one (1) hour after completion

_of

_placing,

_rrr"

_top

_of

_the

_p.v.c.

tubing is sealed

with

a steel

cover.

(See

_Fig.

_S]ql.

-DETERMINATION

_OF

_SO''

_COEFFICIENT

OF

PERMEABILITY

(a)

when

possible,,permeability

_of

_soil

should be determined

_by

testing.

Two

common

raboratory

_methods

_of

_..t".*ining

the

permeab'ity

constant

(K)

are:_

constant-head permeameter test _;

falling-head _{permeameter test}

(b)

There

are

tabres.

_{and nomoslaphs}

_developed

_fbr

estimating

soil permeability

_coefficient.

_A

_tabre

prepar"o uy-rupun _{Road Association} (see _Table

.5.1).and a

nomograptrby

Moulto"

i!;"

Fig. 5.r0)

can be used

for

estimating soil permeablHty _coefficient.

(c)

_{Besides raboratory testing, measurement}

of

soil permeability _{shourd be}

made

in

the

_{field by}

_{adopting one}

_of

_the

_above

_two

methods, after a

normal _{borehole test has been carried}

out.

5.6.1

In-situ permeability

_Test

(a)

Variable

Head

in

Soils

(1) (2)

fh.".

r"r:u^O

31d

typlcll

recording

of

the

rest are presenred

in

Tables

_5'2'

_{5.3 and}

_5'4.

_The

_coificients

of

p"r-"uuitity

_at

_tte

depth

of

_{borehole are determined}

_by

_using

the so calred iailing_

head

_{method' water in}

_the

_borehole

is filred

up to

the

top

of

casing and the change

in

water

level

_with

_{time is monitored}

_for

a _{period of time.}

The formula

_for

_computing

_the

_coefficient

_of

permeability

_is given as

follows:-K=

2nP.

1 1 (r2- t1) H1 1og" H2

coefficie_nt _{of permeabiliry (cmlsec)}

radius

of

casing (cm)

initial

testing time (minute)

final

testing

time

(minute)

initial

head

final

head 5-9

K=

R=

f._!l -L2=

H1

₌

Hr=

;"J#." where

(a)

Variable

Head

in Soils

-

(Cont'd)

The formula

for

determining

the coefficient

of

permeability

from

packer test results

is

given

in

the

United

States Bureau

of

Land Reclamation "Earth

Manual"

(1963)

as:-a

K =

-x

1og"(L/r)forl>10r

2nLH,

where

K =

coefficient

of

permeability (cm/sec)

a =

rate

of

flow

(cu.cm.sec)

L =

test section length (cm)

Ht =

total dynamic head (cm)

r

₌

radius of test hole (cm)

(b)

Packer

Test

in

Rock

A

single packer

is

lowered

to

the

required depth, and

is

supported

on

drill

rods,

which

are

also used

to

supply

water

under pressure

to

the test

section.

At

the

top

of

the

drill

hole,

the rods are connected

via

a

water swivel

and a

high

pressure

piston water supply pump

capable

of

delivering

at

least

100

litres/minute.

In

addition, at the

end coupled

to

the

swivel

hose, one pressure gauge and a volumeter are included to allow

the measurement

of

water

flow

and pressure

in

various stages.

The

test

carried out

in

stages

being cycled up

to

a

maximum head and

then down

again.

In

the

case

of

leakage (unsound

rock), the test is performed only

for

the attainable pressure.

At

each pressure stage,

the

pressure

is

held

constant and the

volume is measured over a period

of

5 minutes.

The permeability is calculated

from

the volume

of

flow

and the net dynamic head applied to the test section"

The net dynamic head (Ht)

is:-Ht =

(Hp+Ht+Hz)-H"

where

Hn =

the pressure head (from the pressure gauge)

Hr =

head due to the height of the pressure gauge

above the ground level

Hz =

depth

of

ground water or middle

of

test section

if

the

drill

hole is dry

H" =

head loss

in

the equipment

Note:

In rocks with a permeability of less than 1

x

10-s cm/s,

(H")

is

not likely to be significant and therefore negligible.

5-10

j

i

CTMTNT MIXID WITH SAND

GROUND LEVEL PIPT GROUND LtVtL COARST SAND

1m

SAND P.V.C. COVER COARST SAND

FIG.

5.8

STANDPIPE INSTATI,ATION

FI

3

_|

nrnronnrro

o

₎

SECTION

COVER

CEMENT MIXID WITH

GROUND LTVEL

19mm l.D. P.V.C. PIPE

GROUND LEVEL

CTMENT BENTONIK SLURRY

T-t.oml t

sOlL/sAND BACKFTLL

(BonoM oF BORrHOLT)

FIG.

5.9

PIEZOMETER STANDPIPE

INSTALI.{TION

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'"1 I l l j l a l.

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5-15 j

DATE TIME W.L. MEASURED FROM

GRoUND LEVEL (m)

DATE TIME W.L. MEASURED FROM

cRoUND LEVEL (m) 18/06t87 23.93 04/07t87 26.71 19/06t87 24.21 05t07 t87 26.63 20/06t87 _{24.46 a6/07t87 26.53} 21/A687 24.67 07t07t87 26.22 22/06t87 24.9 a8/07t87 26.01 23/06t87 23.97 09ta7t87 25.85 24/06t87 _{23.99 10/07 t87 25.88} 25/06t87 24.25 11t07 t87 25.90 26/06187 _{24,38 12tA7t87 25.91} 27/06t87 _{24.45 13/07/87 25.92} 28106t87 _{25'Qt 14t07 t87 25.94} 29106t87 _{25.24 15/07t87 25.92} 3A/06t87 2s.52 16t07t87 25.93 01/47 t87 25.58 02/07t87 _25.64 03t07t87 _25.68

TABLE 5.4

-

MEASUREMENT OF W.L. FOR STANDP!PE / PIEZOMETER STANDPIPE No. oF STANDPIPES

:

BH4

(INSTALLATION oF STANDPIPE DEPTH To 30.70m b.g.l)

5-1 6 (Aug 02)

C:\REANAT5.4-Standpipe.xls(IMfVct)

r-5.7

DESIGN

OF

FILTER

MATERIAL

In

the past

little

attention has been paid

to

the nature

of

the material

backfill

into the drainage trench and that surrounding the drain

pipe. It

has been found

that the

usage

of

unsuitable

filter

material has

resulted

in

an

inefficient

drainage system,

which

after

few

years has ceased

to

function owing

to

the

siiting up

of

the

backfill.

In

addition, where

the

drains are installed

in

silty

sandy

soi1,

fine

silts are often

washed

through the voids

leading

to

the

formation

of

large voids

(also

known

as

"soil piping"

or

"internal

erosion")

which

have caused

failure

in

pavements due

to lack

of

the structural

integrity

of the underlying soil.

General characteristics required for the

filter

material are:-(a)

(b)

the stability

of

grains, i.e. not early weathered nor dissolved.

proper gradation,

well

graded natural gravel

or

graded crashed

rock

is most suitable.

it

must prevent

finer

material, usually the subgrade soil, from

piping

or migrating

into

the drainage layer and clogging it.

it

must be

permeable enough

to

carry water

without

any significant

resistance.

Filter _{material selected must be able to}

_fulfill

_these

requirements:-(a)

(b)

(c)

it

must be strong enough

to

carry the loads applied and,

for

aggregate

filters, to distribute

live

loads to the subsrade.

Filter

material

can

consist

of

standard

/

design gradings

of

soil

particles

or synthetic

filter

cloth.

The procedure,

which is now

commonly adopted,

is

to

use specially selected or designed

filter

materials.

5.7,1

Design

Filter Material

-

standard

Gradings

and Design

Gradings

The aim

of filter

design

is

to ensure that the pores

in

the

filter

are

fine

enough

to

prevent

the migration

of

coarser

soil

particles

(soil piping)

which

will

support the soil mass.

Filter

design criteria therefore needs

to relate

to

the pore size

of backfill

material

and the

particle

sizes

of

the

soil

around

the drain,

filter

material must

also

be

sufficiently

permeable to

allow

the

flow

of

water.

The design

life

of

filter

material

should be 10

to

15

Years.

Generallv" we have to desisn

filter

materials

for:-predominantly clay soils

predominantly sandy or gravel soils (a)

(b)

(a)

_{Predominantlv}

_Clav

_Soils

Concrete sand

complying to

MS

30,

Zone Z grading

or

similar

material

has

proved

quite

satisfactory

for all

silty

and

clayey

soils.

The

concrete sand

is fine

enough

to

act

as

a

filter

for

silts,

and

will

protect

_{the drain from any fine}

_non-cohesive

particles

in

clays.

Fig.5.11

and

Table 5.5 show the

particles size distribution

for

concrete sand

MS

30.

Table 5.5 - The Particles Size _{Distribution for concrete Sand MS 30}

Predominantly

Sandy

or Gravel

Soils

The

first

step

in

the design

of

filter

material

for

sandy

or

gravel soils

is to

obtain a

particle

size analysis

of

the subgrade

soil

in

which

it

is

prop.osed

to install

the

drain

and

to

plot

a curve

of

particle size

distribution in

the usual manner. The

limits

for

the

particle

size

distribution

of

the

filter

materials are based on the requirements shown

in Fig.

5.12.

(i)

Filtration

or Piping Ratio

To

prevent

silt

or fine

particles

of

the

base

soil

from

being washed

into

the

filter

material

(soil

piping).

(See

Fig.5.12).

Drsp

<5

D85S

Permeabilitv Ratio

To

ensure

that the

filter

material must have

a

higher permeability rate than that of the subgrade.

Drsr

>5

(b)

(ii)

8.S.410 Test Sieve Percentage by Weight Passing B.S. Sieves 10.0

mm

100 5.0 mm ₉₀

-

100 2.36

mm

75

-

100 1.18

mm

_55-90

600 um

_35-59

300 um

_8-30

150 um

_0-10

Drss

5-1 8 -..--,i

CN U J co O a J E U U) E. U z. E; (n o z. 6

-

_U U z. c; U) F J U1 t! U)

=

o U U z. d

I

.fj

I

h

E E Ld N,I lr I -J

=

E o_ SNISSVd

]CVIN]3U]d

ogsooooooo

_{qtcOl-.@n+nN;}

oaaooooooo

_o)oN@tr)*.N; CNISSVd

:CVIN]3U]d

E E E 3 I i *itr&i. 5-19

(b)

_{Predominantly}

_Sandy

_or

_Gravel

_Soils

(iii)

Hole Ratio

For

the

filter

material

to

be

carried

away

through the

holes

followins

must hold:

-

(Cont'd)

prevented

from

being

of

the drain

pipes, the

Dasp

D

(diameter

of

hole) Notes:

(1)

Dtsp is

used

to

designate

the size

of

the

sieve

that

allows fifteen

percent

(l5%o)

_by

_weight

_of

_{the filter}

material

to

pass through

it.

Similariy,

Dass designates

the

size

of

sieve

that

allows eighty-five

(852o)

by

weight of

the base

soil

to pass through

it.

particle

sizes

smaller than

the

75 um

sieve refer

to

Hygrometer

analysis results.

(2)

The

filter

must not be gap-graded (i.e. when some sieve

fractions

are scarce

or

missing altogether).

Where the

soil

around a drain

is

gap-graded,

filter

design shall be

based

only on

the particles

finer

than

the

gap

in

the

grading.

Such precautions

are

intended

to

ensure that

the finer soil

cannot migrate through

the

coarser

particles and therefore clog the drain.

(3)

If

the soil contains layers

of fine

material, the

filter

shall

be designed

from

the grading of the

finer

soil.

(4)

Filter

material

shall not

have more than

five

percent

(5%)

of its

weight

passing through the 75

um

sieve, to

prevent migration of fines from the

filter

into the drain.

Examples

in

Section 5.7.3 show

how

to

design

filter

materials

for different

types ofbase soi1.

5.7.2

Synthetic

Filter

Cloth / Fabrics

The

recommended

minimum

engineering

fabric

selection

criteria

in

filtration

/

drwnage applications shall be as

follows:-Pipins

Rgsistance

(all

applications)

(i)

soils

with

50Vo

or

less

particles

by

weight

passing 75

um sieve; EOS

<

Dss

of

adjacent soil

(ii)

soils

with

more than 50Vo partrcles by weight passing 75

um sieve;

(iii)

the

Equivalent Opening Size shall

be

obtained

in

the

following

manner:-(a)

5.7.2

Synthetic

Filter

Cloth /

Fabrics

-

(Cont,d)

Five (5) fresh samples shall be tested.

About

150 gm

of

each

of

the following

fractions

of

sand composed

of

sound rounded

particles shall be as tabulated

below:-Table 5.6 - Composition of Sand Fraction From 150 gm Samples Percentage Passing _{Percentage Retained On}

l0

₂₀ 20 ₃₀ 30 ₄₀ 40 50 50

_t0

100 ₇₂₀

(iv)

The cloth

shal1

be fixed

to

a

standard

sieve

having

openings

_{larger than the}

_{coarsest sand}

_used

_in

_such

manner that no sand can pass between the

cloth

and the sieve

wall.

The sand shali be

oven-dried.

Shaking shall be accomplished as described

in ASTM

D422, and shall

be

continued

for

20

minutes.

Determine

by

sieving

(using

successively coarser

fractions)

that fraction of

sand

of

which

five

percent

(5Vo)

_or

_less

_by

_weight

passes the cloth: _{the equivalent opening size}

_of

_{the cloth}

sample is the "retained

on"

Standard

Metric

sizes

of

this

fraction. Notes:

(1)

whenever possible,

fabric

with

the

iargest possible EOS shall be preferred.

(2)

when

protected

soil

contains

particles

25mm

size

to

those passing the

_{U.S. 75 um}

sieve, use

only

the gradation

of

soil

passing the

U.S.

4.75

mm sieve

in

selecting the fabric.

Cloesins

Resistance

(i)

Severe

/

cntrcal applications:

+

_woven

_fabrics

_percent

_open

_area

_>

_4.0Vo

_and

EOS

>

150 um sieve (0.149 mm);

**

_{woven fabrics not meeting}

_item

_(*)

and al1 other

fabrics gradient ratio

<

3.0;

(ii)

Less

severe

I

less critical

applications

all

fabrics

equivalent

Darcy

permeability

_of

_fabric

_>

₁₀

_times Darcy permeability

of

soil to be drained.

(b)

(c)

Chemical Composition Requirements

(i)

Fibres

used

in

the

manufacture

of

engineering fabrics

shall consist

of

long-chain synthetic

polymer,

composed

of

at least 85Vo

by

weight

of

polypropylene, ethylene,

-ester amide, or-vinylidene-chloride,

and shall

contain

stabilizers and

/

or

inhibitors

added

to

the base plastic

(as

necessary)

to

make

the fabric

resistance

to

deterioration from

ultraviolet

and heat exposure.

(ii)

The

engineering

fabric

shall

be

exposed

to

ultraviolet

radiation (sunlight)

for

no more than 30 days total

in

the

period

of

time

following

manufacture

until

the

fabric

is covered

with

soil, rock, concrete, etc.

(d)

Physical

Propertv

Requirements (all

fabrics)

Table

5.7

-

Physical

Property

Requirements

Fabric (*)

Unprotected

Fabric

Protected

Grab Strength

(ASTM

D

1682) 0.9

KN

0.45

KN

Puncture Strength xx

(ASTM D

751-68) 355

N

155

N

Burst Strength xxx

(ASTM D

751-68) 2.2

KN/m

1.1

KN/m

Notes:

*

_Fabric

_is

_said

_{to be}

_protected

_when

_used

_in

_drainage

trenches

or

beneath

/

behind concrete (portiand

or

asphalt cement)

slabs"

A11 other

conditions

are said to be unprotected.

**

_Tension

_testing

_machine

_{with ring}

_clamp,

_{steel ball}

replaced

with

an

8

mm

diameter

solid

steel

cylinder

with

hemispherical

tip

centered

within

the

ring

clamp.

+{<{<

_{Diaphragm test method.}

-r-- --- i a1 _?E:.gj'-Pr

5.7.3

Examples of

Filter

Design Example 1

suppose

a

subsoil

drain

is to

be

constructed

in

a

base

soil

with

gradings as shown in Fig. 5.12.

(a)

For

Filtration

D15F Dass

=

D15F

<5 x

Dess

5

x

0.25

(fromFig.5.t2)

=

l,.25mm

hence, D15F

<

1.25mm

(b)

For Permeability D15F

;>s

=

D15F>5xDtss

5

x

0.02

(f6omFig.5.12)

=

0.10mm

hence,

D15F

>

0.1mm

A

backfill

material

should

be

chosen

for

the drain that

is within

the

specifications above. Please note

in

Figure 5.12

thatit

is

desirable that the gradation curve

of

the

filter

material

is

smooth and

parallel to

that of the subgrade.

Example 2

A

subsoil drain

is to

be

constructed

in

a

base

soil

with

gradings as

shown in Fig. 5.13.

(a)

Filter

Design

<5

l l j : -j j I *i

(i)

For

Filtration

D15F

<5

l

,

_Dlss

*-il ;;

;

-

D15F<5.rDsss

"i

=

5x0.21(fromFig.5;13)

i

=

1.05mm

hence,

Dtsr

<

1.05mm .: '-': :

<12

I J-LJ

*-;it-80 b's F

z

L!.1

cr60

U o-z. a

i?40

o_ ALLOWABLE RANGE 0F Des (FILIER) , I N CURVT FILTIR MATTRIAL

0.5

'l SIEVI SIZE (mm)

FIG.

5.12

GRADATION

OF

FILTER

MATERIAT

SAND GRAVTL 100

z.

U) 6U a o_

,.60

U

z+0

UJ

*:

L! ?n o- --0 0.05 0.1

1.0

₁₀ GRAIN

SlZt

(mm)

NG.

5.13

NTTER

Ai'ID SIOT

DESIGN FOR EXAMPI.E Z 2D (HOL[ StZ

HOLE SlZt

=

l0mm

GRADIATION CURVE OF SUBGRADE

5 Drs (SUBGRADE)

= P.1rt

ALLOWABLI RANGE 0F D1s (FILTER)

/

'

BASE SOIL TO

-

BT FILTERTD

/

/

CALCULATED FILTTR MATTRIALS

)

5-2/+

5.7.3

_{Examplesof FilterDesign}

_-

_(Cont'd)

(ii)

For Permeability

D15F

>5

D155

=

D15F>5xDtss

=

5

x

0.085 (from Fig. 5.13)

=

0.425mmhence, D15F

>

0.421mm

(b)

Slot Design

A backfill

material should be chosen

for

the drain that is

within

the specification given above.

A

suitable

material

might

have 85vo size

of

between 3-5mm.

The maximum

allowabie

hole

sizes

in

pipes used

with

the

material would be given

by:-Maximum dia. of circular

hole

=

Dssr

Maximum

dia. slots width

₌

_Dssp

_x

1

7.2

(a)

For

Filtration

D15F

<5

Dsss

Drsp<5xDsss

5

;

1.05 (from Fig. 5.1a)

5.25mmhence,

D15F

<

5.25mm

=

5.0mm

=

4.2mm

If

the

holes

in

the

pipe

are

too

large,

a

coarser

filter

material must

be

placed

next

to

the

pipe.

The grading

of

the

coarser

material must be able to prevent

migration

of

the

filter

into

the

pipe.

It

should therefore

be

designed

in

_{the way}

_indicated

above, except that the

finer filter

material

is

considered as the base soil.

Example 3

A

subsoil drain

is

to

be

constructed

in

a

base

soil with

gradings as

shown

in Fig.

5.14.

COBBLES

SILT SAND GRAVEL

100 E-U 2.80 L-L! ^^

s

2.,^

LI +U U.

u^^

o_ 4u 0.01 0.1 1.0

Sltvt

SIZE (mm)

100

FIG. 5,14

FITTER DESIGN

FOR

EXAMPTE 3

BASE JI IL TI rEREI

I

)

CALFILI :UI :R \TFD UATE (l ,L 5-26

5.7,3

Examples of

Filter Design

-

(Cont'd)

(b)

For Permeabilitlz

Drsr'

>5

D155

The backfiil

chosen grading

limits.

D15F>5xDtss

5

x

0.025 (from

Fig.

5.14)

0.125mmhence,

Dtsp >

0.125mm

for

the drain

should

lie

within

the

calculated

TYPES OF SUBSOIL

DRAINS

The type

of

subsoil drain to be used

will

depend

mainly

on the source and the

volume

of

water to be handled.

A11 subsoil drains should

be

surrounded

with

an appropriate

filter

to

prevent

soil

piping

and at the same time have adequate

conductivity

to remove seepage

flow.

Granular

or

synthetic (Geotextile) materials

_{can be}

used

us

iilt"t

membrane

and

free draining

aggregates

with

or

without

a

subsoil

pipe

is

commonly used as the water conductivity medium. Four (4) types

of

subsoil drain commonly used

are:-(a)

single size aggregate

filled

trench

lined

with

synthetic

filter

cloth

(See

Fig.5.15);

(b)

subsoil pipe and single size aggregate

filled

trench

lined

with

synthetic

filter

cloth (See Fig. 5.16);

(c)

porous

/

perforated

/

slotted

pipe

with

design

filter

material

(See Fig.

5.17):

other proprietary types.

5.8.1

Single Size Aggregate

Filled

Trench

Lined

with

Synthetic

Filter

Cloth

(See

Fig.5.15)

In

this type

of

subsoil drain, the trench

is lined

with

geotextiles (made

up

of

very

fine

holes and high porosity) protecting gravel

filled

trench. The geotextile acts as a

filter

as

it

allows water seeping

from

the soil to

pass through

while

preventing

most

soil

particles

from

being

carried away by seepage water.

5.8

(d)

5.8.1

Single Size Aggregate

_{Filled Trench Lined with}

Synthetic

Filter

Cloth

(See

_Fig.

_5.15)

-

(Cont,d)

This type

of

subsoil

drain

requires

and can

handle

only

relatively

However, this type

of

subsoil drain of geotextile material.

The

recommended

minimum

geotextile

selection

criteria

in

filtration

applications is discussed earlier

in

detail under Section

5.j.2.

less

control

of

aggregate gradings

low

seepage

volume

of

water.

is

quite

expensive due to

high

cost

5.8.2

Subsoil Pipe and Single Size

Aggregate

Synthetic

Filter

Cloth

(See

_Fig.

_5.16)

Filled Trench Lined with

It

is

a combination

of

subsoil

pipe

and aggregates.

It

can handle large seepage

volume

of

water

but

is

even more

expensive

than the

type mentioned under Section 5.8.1.

5.8.3

Porous

/ Perforated

/

slotted

Pipe

with

Design

Filter Material

(See

Fig.

5.17)

consists

of

a

trench

in

which a line

of

subsoil

pipe

is

laid

and the trench

backfilled

with

suitable

fiiter

material.

The common types of pipes available are

follows:

(i)

(ii)

(iii)

(iv)

porous concrete plpes

asbestos cement slotted pipes perforated PVC pipes

unglazed earthenware

This

type

of

subsoil

drain

requires

_{stringent control}

_of

gradings and can handle

large

seepage

volume

of

water.

Among the

four

if

is

the cheapest type

of

subsoil drain.

5.8.4

Other

Proprietary

Types

Currently

in

the market, there are other patented types

of

subsoil drain

which are

marketed

by

various

manufacturers.

Proprietary

types

should

be

given due

consideration

and there

is no

reason

why

they cannot be used

if

they a.re proven to be suitable after proper evaluation

and

field

tests as

described

under

Section

5.4.r.

If

in

doubt,

the Engineer should refer the new products to

IKRAM

for

advice.