FOREWORD

Road Engineering Association of Malaysia (REAM), through the cooperation andsupport of various road authorities and engineering institutions in Malaysia, publishesA SETiES Of OffiCiAl documents on STANDARDS, SPECIFICATIONS, GUIDbLINES,MANUAL and TECHNICAL NOTES which are related to road engineering. Theaim of such publication is to achieve quality and consistency in roa-d and highwayconstruction, 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 onTechnoiogy and Road Management organized by PWD/REAM in Novemb er I99J,Technical Committee 6 - Drainage was formed with the intention to review ArahanTeknik (Jalan) 15/97 - INTERMEDIATE GUIDE To DRAINAGE DESIGN oFROADS. Members of the committee were drawn from various governmentdepartments and agencies, and from the private sector inciuding privitized roadoperators, engineering consultants and drainage products manufacturers andcontactors.

Technical Committee 6 was divided into three sub-committees to review ArahanTeknik (Jalan) 75/91 and subsequenrly produced 'GUIDELINES FoR ROADDRAINAGE DESIGN' consisting of the following volumes:

Volume I - Hydrological AnalysisVolume 2 - Hydraulic Design of CulvertsVolume 3 - Hydraulic Considerations in Bridge DesignVolume 4 - Surface DrainageVoiume 5 - Subsoil Drainage

The drafts of all documents were presented at workshops during the Fourth and FifthMalaysian Road Conferences held in 2000 and 2002 respectively. The comments andsuggestions received from the workshop participants were reviewed and incorporatedin the finalized documents

ROAD ENGINEERING ASSOCIATION OF MALAYSIA46-4, 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... ..".,..5-25.3.1. The Control of Seepage Flow in Rollinsor 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 aPervious Road Surface........ . .

DESIGN FLOW CAPACITY5.4.1 Field Trial Method.

5.4.2 Calculation Method

5-2

5.4

3.t

DETAILED SUBSURFACE INVESTIGATION......... 5-85.5.1 Boring and Ground WaterLevel Measuremer;:........"..............5_g

5 .5 .2 Standpipe . . .5_g5.5.3 Piezomerer Standpipe

. " ..5_g

DETERMINATION OF SOIL COEFFICIENT OF' PERMEABILITY ....5-95.6.1 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_r75.7 .2 Synthetic Filter Clorh / Fabrics .....5_205.7.3 Examples of FilterDesign. ..."5_23

TYPES OF SUBSOIL DRAINS ..... ....5-275.8.1 Single Size Aggregates Filled Trench Linedwith Synthetic Filter Cloth (See Fig. 5.15) ...

-tII

-lII

'III

III

1II

II

t

;*--

Subsoil Pipe and Single Size Aggregate Filled TrenchLined with Synthetic Filter Ctottr qsie Fig. 5.16) .....,Porous / Perforated / Slotted pipe withDesign Filter Material (See Fig.5.17) ...Other Proprietary Types

.. "....5-21

5-28

.5-28

5-28

5.9 DRAIN PIPE DESIGN..5-29

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

Table 5.7 Physical Property Requirements ... ..5-22

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 internalmoisture control, a properly designed and incorporated ,uu*it drarnagesystem 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 retentionand movement within, constitute the two important phases in soii moisturerelationship' Water movement takes place fy trr" action of gravity or ofcapillary 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 pavedsurface.

The principal objective of subsoil drainage is to make sure that a subgrade ofuniform bearing value and strength is maintained.

The principal ways in which changes in moisture conrent can occur in thesubgrade of a road are:_

VOLUME 5, SUBSOILDRAINAGE

by lhe seepage of water into the subgrade from higher ground adjacentto 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 watertable in a flat terrain);

by the percolation of water through the surface of the roadcarriageway.

(a)

(b)

(c)

<) PROVISION AND LOCATION OF SUBSOIL DRAINAGE

The decision to install subsoil drainage should be based on site conditionsexisting at the time of construction. where position oi ,t " water table isreasonably close to formation level (about im or less), the Engineer isrequired to carry out soil classification tests, grading tests and trial pits toascertain the level of the water table. The mosiapprolriut" time for .uoylngout the trial pits is during the wet months when ttre iater table is usualy at itihighest level and the subsoil at its wettest. It is the responsibility of theEngineer to determine the necessity and locations where subsoil drainage isrcquired' The Engineer then foliows the procedures specified under Section5.7 in order ro select and design firter material suitabi" f* ih;'^ryp"ffi"rrencountered.

5-1

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 toacceptable level before it reaches the road structures (see Fig. 5.1);

the removal of stationary water in the soil to control and to lower theground 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 constructionperiod (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 isdeep, it is generally, impracticable to construct the drainage trenchsufficiently deep to intercept all the seepage water.

ln this case, therefore, the intercepting drain is usually located to keepthe 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 subsoildrainage system. It is desirable that the water table should bemaintained at a depth not less than 1m below formation level (see Fig.5.3). The actual spacing and depth of drains to achieve thisrequirement will depend on the soil conditions and width of the roadformation. 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 SubgradeThrough a Pervious Road Surface

A completely impermeable road surface is difficult to reaiize inpractice and porous subbase has been installed to deal with waterpercolating through the pavement surface.

[ 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

5-3

NG. 5.4 SUBSOII DRAIN FOR MUTTII,ANES ROAI)

SHOULDER

SUBBASE

DESIGN FILTERl'/ATERIAL

MINIMUM 150mm 0 SUBSOIL PlPt

FIG. 5.5 SIESOIT DRAIN TO DIRECTTY DRAIN TIIE BASE COT]RSE

WATIRTABLE

ROADSIDIDRAIN

SETPAGEZONE

IMPIRVIOUSSTRATUM

DESIGN FILTER MATERIAL

l/lNiMUM 150mm 0 SUBSOIL PIPE

NG" 5.6 IIVTERCEPTION OF SHATLOT SEEPAGE ZONE

SHOULDER

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5.3.3 The Control of Water Entering the SubgradeThrough a Peryious Road Surface - (Cont'd)

(a) Porous Subbase

The purpose of the porous, granular subbase is to trap any waterinfiltrating through the road surface and carry it to the open drainsprovided beyond the road shoulders and so prevent the softening ofthe subgrade. The porous subbase consists of i50mm to 300mm ofcompacted porous rnateriai such as sand, gravel, etc., interposedbetween the base course and the subgrade (see Fig. 5.5). Thesubgrade, has to be properly cambered and free from depressionsand the porous subbase must cover the entire road formation andconnected to the roadside drain. Unless very careful attention isgiven to the shaping and cambering of the subgrade, it is probablethat most of the water passing into the porous subbase would betrapped in irregularities in the surface of the subgrade, andconsequently not entering the drain.

Besides acting as a drainage layer, the porous subbase increases thethickness of the pavement design. It also prevents soft clayworking up into the base course of a flexible pavement founded ona ciay subgrade. It is placed immediately after the preparation ofthe formation, and will help to prevent the disturbance of thesubgrade by construction traffic. It is probable that the improvedperformance of roads with porous subbase is due to the latter factorrather than the possibie drainage, which the subbase effects.

DESIGN FLOW CAPACITY

Commonly, the design flow capacity of ground water drainage system is basedon empirical rule of thumb that have been developed by trial and error over aperiod of years, or on rather tedious graphical techniques involving the use offlow nets. The purpose of this section is to present a field trial and errormethod and an approximate analytical method.

5.4.1 Field Trial Method

Where earthwork has reached formation level, a useful estimate of theeffect of installing drains to lower the level of the ground water at aparticular site (see Fig. 5.3) can be obtained by carrying out a simplefield trial. Two parallel trenches 500mm wide and about 20m long are

. dug along the line of the proposed drainage trenches for the road to adepth of about 1m below the leve1 to which it is desired to lower theground water. A transverse line of boreholes at about 1.5m to 3mintervals is sunk between the centre of the trenches and extended about3m to 6m either side. Observations are made of the levels of the watertable in the boreholes before and after pumping the water out of thetrenches for a sufficient period of time to establish equilibriumconditions. By plotting these results, an estimate can be made of thedrawdown effect of the drain trenches, and by this means it is possibleto establish the correct depth and spacing of the drains. The capacityrequired for the drainpipes can be estimated from the rate of pumpingnecessary to keep the trenches free of water.

5-6

x:l

I

5.4

5.3.3 The Control of Water Entering the SubgradeThrough a Pervious Road Surface - (Cont'd)

(a) Porous Subbase

The purpose of the porous, granular subbase is to trap any waterinfiltrating through the road surface and carry it to the open drainsprovided beyond the road shoulders and so prevent the softening ofthe subgrade. The porous subbase consists of 150mm to 300mm ofcompacted porous material such as sand, gravel, etc., interposedbetween the base course and the subgrade (see Fig. 5.5). Thesubgrade. has to be properly cambered and free from depressionsand the porous subbase must cover the entire road formation andconnected to the roadside drain. Unless very careful attention isgiven to the shaping and cambering of the subgrade, it is probablethat most of the water passing into the porous subbase would betrapped in irregularities in the surface of the subgrade, andconsequentiy not entering the drain.

Besides acting as a drainage layer, the porous subbase increases thethickness of the pavement design. It also prevents soft clayworking up into the base course of a flexible pavement founded ona clay subgrade. It is placed immediately after the preparation ofthe formation, and will help to prevent the disturbance of thesubgrade by construction traffic. It is probable that the improvedperformance of roads with porous subbase is due to the latter factorrather than the possible drainage, which the subbase effects.

DESIGN FLOW CAPACITY

Commonly, the design flow capacity of ground water drainage system is basedon empirical rule of thumb that have been developed by trial and effor over aperiod of years, or on rather tedious graphical techniques involving the use offlow nets. The purpose of this section is to present a field trial and errormethocl and an approximate analytical method.

5.4.I Field Trial Method

Where earthwork has reached formation level, a useful estimate of theeffect of installing drains to lower the level of the ground water at aparticular site (see Fig. 5.3) can be obtained by carrying out a simplefield trial. Two parallel trenches 500mm wide and about 20m long are

. dug along the line of the proposed drainage trenches for the road to adepth of about 1m below the levei to which it is desired to lower theground water. A transverse line of boreholes at about 1.5m to 3mintervals is sunk between the centre of the trenches and extended about3m to 6m either side. Observations are made of the levels of the watertable in the boreholes before and after pumping the water out of thetrenches for a sufficient period of time to establish equilibriumconditions. By plotting these results, an estimate can be made of thedrawdown effect of the drain trenches, and by this means it is possibleto establish the correct depth and spacing of the drains. The capacityrequired for the drainpipes can be estimated from the rate of pumpingnecessary to keep the trenches free of water.

5-6

f

s.4.2 Calculation Method

It is always desirabre to carry out design flow carculations for thefollowing reasons:-

to predict the reduction in the water level dueof subsoil drainage;

severe cases where project areaexcessive seepage.

is of high water table or

application of the law needsdetermine the permeability

(a)

(b)

to the provision

Darcy's Law is commonly used anddetailed subsurface investigatio"--.;;constant (k).

calculation of design flow is sometimes omitted in the design ofsubsoil drainage. This is due to the faci that sorvinJ rrr" d", equationsunder complicated actual ground conditions is difficult.

Darcy's Law:

awhere 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 drainagealthough it assumes raminar flow anJ-.onstant viscosity of the water.The use of Darcy's Law requir", u i"r"rroination or tne permeabilityconstant (k) and the hydraulic gradient (i) u"J tr,"r. *";;r"es are noteasily obtainable under foln]i_la1eo grouno conditions. so,,'" typicalvalues 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-l

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 formationlevel, 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 wheneach water level measurement is taken"

5.5.2 Standpipe

Standpipe of 19mm internal diameter rigid unplasticised P.V.C. tubingcan be installed in selected boreholes especially directed. (See Fig.s.8).

The bottom of the standpipe is plugged and the lower 0.5m isperforated with slots.

The perforated tubing is surrounded by a response zone of an approvedgranular 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 preventthe ingress of surface water.

5.5.3 Piezometer Standpip. ,

The piezometer standpipe consists of a porous element 305mm long. Itis 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 isconnected to 19mm internal diameter rigid unplasticised P.V.C. tubingwhich finishes close to ground level. A11 the joints in the tubing are

made with coupling sleeves so that there is no change in the internaldiameter of the bore and it is sealed to be watertight.

5-8,i

,,*-,-ifl.

5.6

5.5.3 Piezometer Standpipe _ (Cont,d)

The borehcire is then seared above the response zone. A stiff grout sealof bentonite 0.5m thick is rhen formed !y ";;;ry a"poriting ; **;;freshly mixed grout. The remainder of irr" ,"ui is tormea by pracinggrout through a tremie tube, the iower eno oi ,ti.t, ,hul'f,"ffibelow the surface of the grout. The grout is then alrowed to settre andset 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'ityconstant (K) are:_

constant-head permeameter test ;falling-head permeameter test

(b) There are tabres. and nomoslaphs developed fbr estimating soilpermeability coefficient. A tabre prepar"o uy-rupun Road Association(see Table .5.1).and a nomograptrby Moulto" i!;" Fig. 5.r0) can beused for estimating soil permeablHty coefficient.

(c) Besides raboratory testing, measurement of soil permeability shourd bemade in the field by adopting one of the above two methods, after anormal 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 inTables 5'2' 5.3 and 5'4. The coificients of p"r-"uuitity at ttedepth of borehole are determined by using the so calred iailing_head method' water in the borehole is filred up to the top ofcasing and the change in water level with time is monitored fora period of time.

The formula for computing the coefficient of permeability isgiven as follows:-

K=2nP.

1 1 (r2- t1)

H11og"

H2

coefficie_nt of permeabiliry (cmlsec)radius of casing (cm)initial testing time (minute)final testing time (minute)initial headfinal 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 ofLand Reclamation "Earth Manual" (1963) as:-

aK =

-x

1og"(L/r)forl>10r2nLH,

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 allowthe 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 oftest 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.

5-10j

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CTMTNT MIXID WITH SAND

GROUND LEVEL

PIPT

GROUND LtVtL

COARST SAND

1m SANDP.V.C. COVER

COARST SAND

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FI

3 | nrnronnrroo ) SECTION

5-11

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CEMENT MIXID WITH

GROUND LTVEL

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

GROUND LEVEL

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T-t.oml

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(BonoM oF BORrHOLT)

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DATE TIME W.L. MEASURED FROMGRoUND LEVEL (m)

DATE TIME W.L. MEASURED FROMcRoUND 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 STANDPIPENo. 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 backfillinto the drainage trench and that surrounding the drain pipe. It has been foundthat the usage of unsuitable filter material has resulted in an inefficientdrainage system, which after few years has ceased to function owing to thesiiting up of the backfill. In addition, where the drains are installed in siltysandy soi1, fine silts are often washed through the voids leading to theformation of large voids (also known as "soil piping" or "internal erosion")which have caused failure in pavements due to lack of the structural integrityof 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 ismost suitable.

it must prevent finer material, usually the subgrade soil, from piping ormigrating into the drainage layer and clogging it.

it must be permeable enough to carry water without any significantresistance.

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 aggregatefilters, to distribute live loads to the subsrade.

Filter material can consist of standard / design gradings of soil particles orsynthetic filter cloth. The procedure, which is now commonly adopted, is touse 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 fineenough to prevent the migration of coarser soil particles (soil piping)which will support the soil mass. Filter design criteria therefore needsto relate to the pore size of backfill material and the particle sizes ofthe soil around the drain, filter material must also be sufficientlypermeable to allow the flow of water. The design life of filter materialshould be 10 to 15 Years. Generallv" we have to desisn filter materialsfor:-

predominantly clay soils

predominantly sandy or gravel soils

(a)

(b)

i:

(a) Predominantlv Clav Soils

Concrete sand complying to MS 30, Zone Z grading or similarmaterial has proved quite satisfactory for all silty and clayeysoils. The concrete sand is fine enough to act as a filter forsilts, and will protect the drain from any fine non-cohesiveparticles in clays. Fig.5.11 and Table 5.5 show the particlessize 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 gravelsoils is to obtain a particle size analysis of the subgrade soil inwhich it is prop.osed to install the drain and to plot a curve ofparticle size distribution in the usual manner. The limits for theparticle size distribution of the filter materials are based on therequirements shown in Fig. 5.12.

(i) Filtration or Piping Ratio

To prevent silt or fine particles of the base soil frombeing washed into the filter material (soil piping). (SeeFig.5.12).

Drsp<5

D85S

Permeabilitv Ratio

To ensure that the filter material must have a higherpermeability rate than that of the subgrade.

Drsr>5

(b)

(ii)

8.S.410 Test Sieve Percentage by Weight PassingB.S. Sieves

10.0 mm 1005.0 mm 90 - 100

2.36 mm 75 - 1001.18 mm 55-90600 um 35-59300 um 8-30150 um 0-10

Drss

5-1 8

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5-19

(b) Predominantly Sandy or Gravel Soils

(iii) Hole Ratio

For the filter material to becarried away through the holesfollowins must hold:

- (Cont'd)

prevented from beingof the drain pipes, the

Dasp

D (diameter of hole)

Notes:

(1) Dtsp is used to designate the size of the sieve thatallows fifteen percent (l5%o) by weight of the filtermaterial to pass through it. Similariy, Dass designatesthe size of sieve that allows eighty-five (852o) byweight of the base soil to pass through it. particle sizessmaller than the 75 um sieve refer to Hygrometeranalysis results.

(2) The filter must not be gap-graded (i.e. when some sievefractions are scarce or missing altogether). Where thesoil around a drain is gap-graded, filter design shall bebased only on the particles finer than the gap in thegrading. Such precautions are intended to ensure thatthe finer soil cannot migrate through the coarserparticles and therefore clog the drain.

(3) If the soil contains layers of fine material, the filter shallbe 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, toprevent migration of fines from the filter into the drain.

Examples in Section 5.7.3 show how to design filter materialsfor different types ofbase soi1.

5.7.2 Synthetic Filter Cloth / Fabrics

The recommended minimum engineering fabric selection criteria infiltration / drwnage applications shall be as follows:-

Pipins Rgsistance (all applications)

(i) soils with 50Vo or less particles by weight passing 75um sieve; EOS < Dss of adjacent soil

(ii) soils with more than 50Vo partrcles by weight passing 75um sieve;

(iii) the Equivalent Opening Size shall be obtained in thefollowing manner:-

(a)

5-20

5.7.2 Synthetic Filter Cloth / Fabrics - (Cont,d)

Five (5) fresh samples shall be tested. About 150 gm of each ofthe following fractions of sand composed of sound roundedparticles shall be as tabulated below:-

Table 5.6 - Composition of Sand Fraction From 150 gm Samples

Percentage Passing Percentage Retained On

l0 2020 3030 4040 5050 t0100 720

(iv) The cloth shal1 be fixed to a standard sieve havingopenings larger than the coarsest sand used in suchmanner that no sand can pass between the cloth and thesieve wall. The sand shali be oven-dried. Shaking shallbe accomplished as described in ASTM D422, and shallbe continued for 20 minutes. Determine by sieving(using successively coarser fractions) that fraction ofsand of which five percent (5Vo) or less by weightpasses the cloth: the equivalent opening size of the clothsample is the "retained on" Standard Metric sizes of thisfraction.

Notes:

(1) whenever possible, fabric with the iargestpossible EOS shall be preferred.

(2) when protected soil contains particles 25mmsize to those passing the U.S. 75 um sieve, useonly the gradation of soil passing the U.S. 4.75mm sieve in selecting the fabric.

Cloesins Resistance

(i) Severe / cntrcal applications:

+ woven fabrics percent open area > 4.0Vo andEOS > 150 um sieve (0.149 mm);

** woven fabrics not meeting item (*) and al1 otherfabrics gradient ratio < 3.0;

(ii) Less severe I less critical applications all fabricsequivalent Darcy permeability of fabric > 10 timesDarcy permeability of soil to be drained.

(b)

l5-2r

(c) Chemical Composition Requirements

(i) Fibres used in the manufacture of engineering fabricsshall consist of long-chain synthetic polymer, composedof at least 85Vo by weight of polypropylene, -ethylene, -ester amide, or-vinylidene-chloride, and shall containstabilizers and / or inhibitors added to the base plastic(as necessary) to make the fabric resistance todeterioration from ultraviolet and heat exposure.

(ii) The engineering fabric shall be exposed to ultravioletradiation (sunlight) for no more than 30 days total in theperiod of time following manufacture until the fabric iscovered with soil, rock, concrete, etc.

(d) Physical Propertv Requirements (all fabrics)

Table 5.7 - Physical Property Requirements

Fabric (*)Unprotected

FabricProtected

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 drainagetrenches or beneath / behind concrete (portiand orasphalt cement) slabs" A11 other conditions are said tobe unprotected.

** Tension testing machine with ring clamp, steel ballreplaced with an 8 mm diameter solid steel cylinderwith hemispherical tip centered within the ring clamp.

+{<{< Diaphragm test method.

5-22

-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 withgradings as shown in Fig. 5.12.

(a) For Filtration

D15F

Dass

= D15F <5 x Dess5 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 thespecifications above. Please note in Figure 5.12 thatit is desirable thatthe gradation curve of the filter material is smooth and parallel to thatof the subgrade.

Example 2

A subsoil drain is to be constructed in a base soil with gradings asshown in Fig. 5.13.

(a) Filter Design

<5

l

l

j

:

-jj

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.:

'-'::

<12I J-LJ

*-;it-

80b's

FzL!.1

cr60Uo-

z.ai?40o_

ALLOWABLE RANGE

0F Des (FILIER)

,

I

N CURVTFILTIR MATTRIAL

0.5 'l

SIEVI SIZE (mm)

FIG. 5.12 GRADATION OF FILTER MATERIAT

SAND GRAVTL

100

z.U) 6Uao_,.60U

z+0UJ

*:L! ?no- --

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 withinthe specification given above.

A suitable material might have 85vo size of between 3-5mm.The maximum allowabie hole sizes in pipes used with thematerial 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<5xDsss5 ; 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 materialmust be placed next to the pipe. The grading of the coarsermaterial must be able to prevent migration of the filter into thepipe. It should therefore be designed in the way indicatedabove, except that the finer filter material is considered as thebase soil.

Example 3

A subsoil drain is to be constructed in a base soil with gradings asshown in Fig. 5.14.

5-25

COBBLES

SILT SAND GRAVEL

100

E-U2.80L-

L! ^^

s2.,^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)

CAL

FILI: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 chosengrading limits.

D15F>5xDtss5 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 thevolume of water to be handled.

A11 subsoil drains should be surrounded with an appropriate filter to preventsoil piping and at the same time have adequate conductivity to remove seepageflow. Granular or synthetic (Geotextile) materials can be used us iilt"tmembrane and free draining aggregates with or without a subsoil pipe iscommonly 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 (SeeFig.5.15);

(b) subsoil pipe and single size aggregate filled trench lined with syntheticfilter 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 withSynthetic Filter Cloth (See Fig.5.15)

In this type of subsoil drain, the trench is lined with geotextiles (madeup 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 topass through while preventing most soil particles from being carriedaway by seepage water.

5.8

(d)

5-21

5.8.1 Single Size Aggregate Filled Trench Lined withSynthetic Filter Cloth (See Fig. 5.15) - (Cont,d)

This type of subsoil drain requiresand can handle only relativelyHowever, this type of subsoil drainof geotextile material.

The recommended minimum geotextile selection criteria in filtrationapplications is discussed earlier in detail under Section 5.j.2.

less control of aggregate gradingslow seepage volume of water.is quite expensive due to high cost

5.8.2 Subsoil Pipe and Single Size AggregateSynthetic Filter Cloth (See Fig. 5.16)

Filled Trench Lined with

It is a combination of subsoil pipe and aggregates. It can handle largeseepage volume of water but is even more expensive than the typementioned 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 thetrench backfilled with suitable fiiter material.

The common types of pipes available are follows:

(i)(ii)(iii)(iv)

porous concrete plpesasbestos cement slotted pipesperforated PVC pipesunglazed earthenware

This type of subsoil drain requires stringent control of gradings andcan handle large seepage volume of water. Among the four if is thecheapest type of subsoil drain.

5.8.4 Other Proprietary Types

Currently in the market, there are other patented types of subsoil drainwhich are marketed by various manufacturers. Proprietary typesshould be given due consideration and there is no reason why theycannot be used if they a.re proven to be suitable after proper evaluationand field tests as described under Section 5.4.r. If in doubt, theEngineer should refer the new products to IKRAM for advice.

5-28

5.9 DRAIN PIPE DESIGN

(a) Diameter of pipe

Minimum diameter of pipe used should be 150mm.

(b) Gradient of Pipe

Absolute minimum gradient: 1 : 300Desirable minimum gradient: i : 100

(c) Perforations

(i) slot width

1.2

(ii) hole diameter

(iii) average surface opening of porous pipe

nThe perforated or slotted pipes shall have holes in the lower half oftheir circumference only. This is to increase the interception ability ofthe pipes and to reduce the in washing of filter materiai.

(d) Cover of Pipe

Subsoil pipes shall have a minimum cover of 300mm (from top of pipeto formation level) if it is not subjected to vehicular loadine. Ii theie-isvehicular loading minimum cover shall be 1.0m.

(e) Subsoil Drain Sumps

Subsoil drain shall be connected into stormwater sumps or under somecircumstances separate subsoil sumps may be necessary. These sumpshave two functions:-

(D For Inspection

usually at the start of a subsoil drain, a simple inspection sumpshould be provided.

(ii) For Cleaning Purposes

Spacing of the sumps should not be more than rz}mapart andhave a minimum horizontal dimensions of 600mm if less than1.2m deep, and 900mm when deeper than that.

5-29

5.9 Drain Pipe Design - (Cont'd)

(0 Pipe Outlet

Pipe outlets should be located at no more than 120m spacing. Subsoildrain outlets shall be constructed on a relatively steep grade to ensureunimpeded pipe discharge. The outlets shall also be paved to preventerosion and to be clearly visible for inspection and maintenance.

Figure 5.19 shows a typical pipe outlet for subsoil drain.

It should be noted that under certain circumstances subsoil pipes canfunction exclusiveiy as a subsoil drain, or be a combination ofstormwater, and subsoil drain. Therefore the types of subsoil drainagewhich do not utilise a pipe cannot be properly maintained and as suchcannot be recommended for permanent installation.

5-30

SHOULDER

ROADSIDT DRAIN

AGGRIGATE BACK FILL

25mm - 40mm STNGLE

SIZE AGGREGATT

ONI LAYTR FILIER CTOTHALt ROUND

FIG. 5.15

ROADSIDE DRAINFORMATION LEVIL

ONE I-AYER. FILTER CLOTHALL ROUND

12rrm - 25mm SINGLISIZE AGGREGATE

MlNl[/UM ] 50mm 0 SUBSOIL PIPE

5.16 SUBSOIL PIPE AND SINGLE SIZE AGGREGATE FILTED

t)

N

5-31

SHOULDER

ROADSIDT DRAINSUBBAST

DESIGN FILTER MATIRIAL

MINIMUM 150mm 0 SUBS0IL PlPt

FrG. 5.17 P0ROUS/PERFORATEp/SL0TTED pIpE

WITH DESIGN FILTER MATERIAI

i (To BE DrslcN[D)

CENTTRLINE

TRANSVTRSE SUBSOIL DRAIN

FIG. 5.18 EXAMPLES OF ARRANGEMENT OF

TRANSVERSE SUBSOIL DRAIN

5-32

-

,75 ,

n I

ttvlL.)

-T I

LONG GALV. SCRTW(stT rN PLASTTC OR

HIAD WALL PLUG)

'l.6mm DlA. GALV.

IHT WIRT TWISTIDAROUND EACH

GALV. WIRINITTING '19mm

(MrsH)

FRONT VIET

SIDE YIET

150mm 0 PIPE

t___-t tr)

-f-TOP VIET

FIG.5.19 TYPICAT PIPE OUTLET FOR SUBSOIT DRAIN

5-33

r--- _

ACKI.{OWLEDGEMENTS

TECHNICAL COMMITTEE 6 _ DRAINAGE

Main Committee Members

Nafisah Hj. Abdul Aziz

Ahmad Fuad Emby

Wan Suraya Mustaffa

Normala Hassan

Teh Ming Hu

Lim Kim Oum

Alias Hashim

Low Kom Sing

Nor Asiah Othman

Johan Les Hare Abdullah

Teh Ming Hu

Wan Suraya Mustaffa

Ahmad Fuad Emby

Lam Kok Hong

Yap Lee Chor

Letchumanan Allagappan

Chairman

Deputy Chairman

Secretary

Alternate Secretary

Committee member

Committee member

Committee member

Committee member

Committee member

Editor

Chairman

Secretary

Committee member

Committee member

Committee member

Committee member

Sub-Committee Members for Volume 5 - Subsoil Drainaee

ACKNOWLEDGEMENTS

Volume 5 is a review of the Arahan Teknik (Jalan) f5/97 - INTERMEDIATEGUIDE TO DRAINAGE DESIGN OF ROADS, the chapter was authored originallyby Soon Ho Sin and Muhamad Amin Mahmud of Public Works DepartmentMalaysia.

Volume 5 now provides guidelines to the practical design of subsoil drainage, withworked examples provided to assist users.

Thanks are due to:

REAM Standing Committee on Technology and Road Management for theguidance and encouragement given in the preparation of Volume 5.

Members of the Technical Committee 6 - Drainage and Sub-Committee forSubsoil Drainage for their untiring efforts to ensure timeiy completion ofVolume 5.